Six Past TumbleStone Posts of Interest to Beginning Tumble Polishers

1) What Do I Need to Start Tumble Polishing Stones Myself? And What Will It Cost Me?

This two part series sets out what a beginning tumble polisher needs and how much it will cost. The costs and details reflect that I live in New Zealand, and the prices were accurate at the time of writing, April 2018. The account aims to be fairly thorough and realistic. Part One covers: The Tumbler; The Siting of the Tumbler; Silicon Carbide Grit; Grit Storage and Tablespoon Measuring; and Disposal of Slurry. Part Two covers: Tin Oxide Polish Powder; Polish Powder Storage and Mixing; Plastic Beads and Bead Storage; Soap for Cleaning and Burnishing; Sieves and Buckets; and Miscellaneous Useful Items.

2) The Seven Stages in Tumble Polishing Stones

This at-present-incomplete Series goes through, step-by-step, the seven stages of polishing stones using a tumbler and 4lb barrel. A set of 40 beach stones collected from Riverton are used to illustrate each stage. Lots of photos show all the steps involved, often following individual stones (the stones are numbered 1 to 40). Stage One is Stone Collection (not usually included in accounts of tumble polishing).  Stage Two is tumbling the stones for about a week in 100 mesh silicon carbide grit, then tumbling them in a soap wash for a few hours. Stage Three involves one week tumbling using 220 mesh silicon carbide grit, followed by a soap wash. Stage Four is the same procedure with 320 silicon carbide grit. Stage Five involves tumbling the stones in a tin oxide “Pre-Polish” powder (five microns in size) for three to five days, followed again by a few hours soap tumble. Stage Six is the “Pro-Polish” tumble, using tin oxide powder of one micron size, for at least one week. Stage Seven is a “burnishing” tumble for a week in borax. Inspecting and sorting of the stones also take place after each Stage.

Posts in this Series to date are:

Stage One, Stone Collection, Riverton, 2-6 November 2017 – Topics include walking the beach, selecting stones, clothing, and equipment.

The Selected 40 Stones – Photos of the rough stones, dry and wet, and brief descriptions.

Stage Two, 100 Grit Tumble, 15-25 November 2017 – Step-by-step account of preparing the barrel and then emptying it after the tumble, disposal of slurry, cleaning of equipment, undertaking a soap wash afterwards, and finally determining weight loss of stones.

The Stones After 100 Grit and Their “Inspection” and “Sorting” Before Stage Three – Photos of the stones are presented after they have been through the 100 grit tumble, then an account is provided of the inspection of the stones, identifying the types of chips and holes and other “imperfections”.

Stage Three, 220 Grit Tumble, 4-13 December 2017 – This Post not only goes through the practicalities involved with the 220 grit tumble but also the inspection of the stones afterwards. 

Stage Four, 320 Grit Tumble, 10-20 March 2018 – A repeat of the steps involved in Stages Two and Three but this time with 320 silicon carbide grit.

The Stones After 320 Grit and Their “Inspection” and “Sorting” Before Stage Five – Some minor issues with a number of stones are presented, illustrated with photos.

Stage Five, Pre-Polish Tumble, 28 August to 3 September 2018 – Includes an account of preparing the tumble and the soap wash afterwards.

The Stones After Pre-Polish and Their “Inspection” and “Sorting” Before Stage Six – This Post includes photos showing all 40 stones as they looked upon initial collection from the beach at Riverton and then upon completion of Stage Five, Pre-Polish, with the stones sitting on graph paper for size comparisons. 

Stage Six, Pro-Polish Tumble, 1 October to 15 October 2018 – An account of tumbling in 1-micron Pro-Polish tin oxide powder.

Stage Seven, Borax Burnishing Tumble, 15 October to 25 October 2018 – Instead of undergoing a short soap wash after the Pro-Polish tumble, the stones are treated to at least one week’s tumbling in borax to help bring out the shine a little more. A summary of the tumbling stages and times is provided at the end of this Post.

The End Result, Stones One to Five – This Post examines how the first five of the 40 Riverton stones have emerged from the polishing process, comparing them with how they looked as rough stones fresh from the beach. Each stone is discussed and close-up photos are provided of their textures, colours and patterns.

The remaining Posts to date are How Stones Six to Ten Have Polished and The Fate of Stones 11 to 15. To Be Continued…

3) The Best Rock Tumbling Book Around – “Modern Rock Tumbling” by Steve Hart (2008)

I read the book referred to in this Post after only a couple of weeks of my own tumbling venture and found it directly relevant and immediately useful. It remains the best I have come across. It is available both as a “real” (paper) book and an e-book.

4) Sources of Detailed Instructions for Tumble Polishing Stones

This Post is a list of seven sources I have found useful for the beginning (and also for the not-so-novice) rock tumbler. They share a number of things in common but often have their own unique ideas or pieces of advice.

5) How Stones Tumble in a Rotary Tumbler

A video is referred to in this Post showing the tumbling action when a barrel is too full or not full enough. A great help in understanding why a barrel should not have too many stones in it!

6) My New Sorting Container for Stones at Different Stages of Tumble Polishing

A good way to store stones which are destined for different stages of tumbling is presented in this Post, so you can group them until you have enough for a barrel load. This also enables you to inspect stones after a tumble and feel free to set aside those that need to repeat a stage.

Diane’s Stone, and an Introduction to Jasper

Just under a year ago, my niece Diane bought a new house in Christchurch. While doing work in the garden, she found a stone that she thought was potentially interesting. She showed it to me when I was visiting her and I recognised it as jasper. The stone was in a rough condition. It was far from smooth, and running through the middle was a brittle and pitted silica band. The photos below are of the stone after it was washed and allowed to dry:

I thought that tumbling it would at least bring out the colour, so I offered to take it away to work on it.

What is jasper? Jasper is a well-known red stone found on many beaches in New Zealand, especially in the South Island. I have found it on beaches like Birdlings Flat in Canterbury, and at Riverton and Gemstone Beach in Southland. It tends to stand out amongst other stones because of its deep red colour:

I once found a rock in a track on the farm I grew up on, The Mains near Waikaka. When trying to identify it, I thought first of all that it was chert but it turned out to be jasper (Minerals.net states that “when Jasper is dull and lacking interesting colors or patterns, it is not Jasper but rather Chert”). I eventually broke it up, with difficulty – to put it technically, jasper “fractures conchoidally” (like flint – Geology.com points out that jasper, chert and flint are very similar, all being varieties of opaque microcrystalline quartz). When polished, the pieces of the rock I found had a very glossy, almost waxy, quality. 

I later discovered that jasper is very common around the Waikaka area, being part of the gold-bearing quartz gravels of the area – see the Tumblestone Posts “Jasper Stones and Petrified Wood, Shepherd’s Creek, Waikaka” and “Waikaka’s Auriferous (Gold-Containing) Quartz Gravels“.

In Riverton, outside the museum Te Hikoi, a number of rocks from Southland are on display. One of them is a large piece of rounded jasper. Inside the museum, a number of smaller jasper stones are displayed, including a dark green one.

When I recently visited Jack Geerlings in Winton, who has an extensive collection of stones and rocks from southern New Zealand, I noticed he had a number of pieces of jasper (see photos below). He had collected some from the Coromandel Peninsula, in the North Island, and generously gave me a piece. Outside his shed, where he had a number of rocks and boulders on display, a rock of red and green jasper can be seen. And inside his shed, he showed me a polished stone of orbicular jasper. In her book “Collecting Rocks, Gems and Minerals” (3rd edition, 2016), Patti Polk has an extensive section on different types of jasper. On pages 121 and 122, in her entry on orbicular jasper, she states: “Orbicular jasper is generally a type of highly silicified rhyolite or tuff that has quartz and feldspar crystallized into radical aggregates of needle-like crystals that form orbicular ir spherical structures.” The photos below include page 122 from her book, illustrating some of the variants of orbicular jasper.

To find out more about jasper, I consulted one of my books, “The Illustrated Guide to Rocks and Minerals” (2015) by John Farndon. On page 204, he notes that jasper is a red, green or yellow variety of chalcedony. Chalcedony arises when quartz crystals forms at low temperatures in volcanic cavities. The crystals can be so small that they are visible only when magnified, which is the meaning of the term “cryptocrystalline”. The general name for cryptocrystalline quartz (also called “microcrystalline”) is chalcedony, which comes in a vast array of colours and patterns. As Farndon notes, it includes blood-red carnelian, wine-red jasper, brown-banded agate, green-moss agate, apple-green chrysoprase, and black and white onyx. The colour depends on what minerals seep into the rock. The presence of iron causes the red colour in jasper. In fact, jasper is often referred to as a coloured form of opaque agate, agate being one of the major types of chalcedony (see, for example, the wikipedia entry on chalcedony).

Mindat.org has a lot of photos of different variations of jasper. Below are also photos of some different types of jasper, with the one on the right showing rough and tumbled stones.

To get back to Diane’s jasper stone: After tumbling for just over a week (9 days and 19 hours, to be precise) in 220 silicon carbide grit (along with other stones), followed by five and a half hours tumbling in water and sunlight soap, the stone’s colours emerged much more clearly. Nevertheless, it was still rough in places, with the middle band of silica especially pitted:

However, the stone showed promise. I next tumbled it in 320 silicon carbide grit for another week (seven days and one hour to be exact), followed by 21 hours in sunlight soap. There was a small improvement in the surface condition of the stone, though of course the pits in the middle silica band were too deep to erode away:

I next tumbled the stone in pre-polish tin oxide for five days, followed by a 21 hour soap tumble. Then it spent nearly 12 days in pro-polish tin oxide, finally spending just over four days in a borax burnishing tumble. Unfortunately, these stages seemed to bring out various lines of weakness in the stone, and it failed to take a polish. I didn’t think that further tumbling would improve it:

While I found this disappointing, it is not unusual for some jasper. Many of the jasper stones found on the beach have a chip out of them or some kind of crack. There is often a brittleness in jasper that gives rise to this. 

At least Diane now has a much cleaner and more colourful stone.

Pre-Polished Batch of Gemstone Beach Stones – Comments on Pre-Polishing

This batch of 64 stones have just been tumbled in a 4lb barrel with tin oxide “pre-polish” powder. This type of tumble is sometimes seen to be optional, with many stone collectors/polishers simply moving straight to the final “pro-polish” tumble once the stones have been smoothed with a fine silicon carbide grit (e.g., 320 or 400 mesh). However, it has become more common for this stage to be included.

For the “pre-polish” stage, I use a tin oxide powder of 5 microns.  A “micron” is an abbreviation for a “micrometre”, or a millionth of a metre, that is, one-thousandth of a millimetre (about .00004 inches). A human hair is, on average, about 75 microns across. Other media can be used for pre-polishing. For example, Steve Hart in his “Modern Rock Tumbling” (2008), reports that he uses 1000 mesh silicon carbide grit which is 4.5 macrons in diameter (page 39). [320 mesh silicon carbide grit is about 29 microns, according to the Washington Mills website.]

The aim of the “pre-polish” stage is to produce a smoother stone than possible with coarser tumbling media. I follow the recommendations that came with the tumbling material I bought from the Rotorua Rock and Gemstone Shop. These are to tumble stones in “pre-polish” powder for between three and five days (note that this is for less than the one week or more recommended for all other stages). “Pre-polishing” assists with the final “pro-polish” stage. After “pre-polish”, the stone is not yet glossy and shiny but is very smooth.

The Seven Stages in Tumble Polishing Stones: Stage Seven, Borax Burnishing Tumble, 15 October to 25 October 2018

(This is the 11th Post in this series – the first Post can be found here.)

Steve Hart, in “Modern Rock Tumbling” (2008), attests that burnishing can make a “significant difference” in the appearance of polished stones (page 44). As one tumble-polisher has put it, “Sometimes stones are a little ‘hazy’ when they come out of the polish and small particles of polish are hidden in the tiny crevices of the stones. It helps to clean them up by burnishing the rocks in soapy water for 4-5 days.”

It was while I was doing my initial internet searches on how people tumble polished stones that I came across the idea of a post-polish burnishing tumble for up to a week using borax. Borax is sold as a white powder that dissolves easily in water. It has been used as a detergent, a food preservative (now banned for this use in some countries), an anti-fungal compound, a weed killer and a low-toxicity insecticide. It is used by tumble-polishers because it is a clean soap, lacking perfume and other additives (some use Sunlight or Ivory soap flakes instead). So I tried it and I thought that the results were great – polished stones seem to sparkle just a little more. Whether this is the case or not, I am not entirely sure, but I have the attitude that if it seems to work, why not continue it! In general, I think that a soap tumble of newly-polished stones for a day is the least that should be done, to remove polish particles and to give a final clean. My established routine practice is a tumble for around one week in one to two tablespoons of borax.

I polished the 40 Riverton stones, that this series is about, in borax for 10 days straight after the pro-polish tumble. This was a little longer than usual as I was busy with other things over this period. Firstly, the washed stones and pro-polish beads were replaced in the 4lb barrel, with water, and then about two tablespoons of borax were added.

001 borax
Two tablespoons of borax in the 4lb barrel in which the stones and plastic beads have been placed, topped by water.

At the end of the tumble, the stones were washed then given a final weighing:

The starting weight of the unpolished stones, right before I began to work with them, was 1605 grams, the end weight is 1244 grams. This means that 361 grams were worn away during the whole polishing process, which is 22.5%, just over one-fifth, of the stone material.

SUMMARY OF TUMBLING STAGES AND TIMES (as taken from Tumbling Log)

(Stage 1 = Stone collection)

Stage 2, 100 grit = 9 days 10 1/2 hours, followed by soap tumble of 12 hours

Stage 3, 220 grit = 9 days 2 hours, followed by soap tumble of 18 hours

Stage 4, 320 grit = 9 days 19 1/2 hours, followed by soap tumble of 3 days 1 1/2 hours

Stage 5, Pre-polish = 5 days 19 hours, followed by soap tumble of 20 hours

Stage 6, Pro-polish = 14 days 5 hours

Stage 7, Borax = 10 days 2 hours

This adds up to the stones spending 49 days and 8 hours tumbling in grit and polish, with an additional 15 days and 5 1/2 hours spent tumbling in soap and borax (a total of 64 days and 13 1/2 hours). Note that this is not the minimum time needed – I often extended tumbling by a day or two in some Stages, and there were occasions where tumbling in soap went on far longer than usual. Furthermore, a smooth beach stone can usually skip Stages One and Two.  

The following Posts in this series look at each of the polished stones in detail to assess the impact of this process on them. The first examines Stones 1 to 5. 

The Seven Stages in Tumble Polishing Stones: Stage Six, Pro-Polish Tumble, 1 October to 15 October 2018

(This is the tenth Post in this series – the first Post can be found here. Apologies for the delay that’s interrupted this series.)

In his book, “Modern Rock Tumbling” (2013), Steve Hart, a mechanical engineer, comments that how a stone becomes shiny after polishing is both a miracle and a mystery:

There is no one who really knows what happens inside the barrel when polish is added to the rocks. The Silicon Carbide stages were relatively easy to understand, because the process was primarily mechanical erosion or abrasion. Not so with polish. There are “mysteries” that don’t add up… There are theories that a given polish may liquefy the top layers of molecules on the rocks and rearrange them so the surface is smoother. Others say it may be an acid/base pH thing, or perhaps a frictional heat buildup phenomenon which causes the rock surface to flow… Another theory is that the rock surface is simply mechanically hammered… down to a smoother condition… After really trying to understand the polish process, I had to give up, because no one… really knows what’s going on (pages 40-41).

Stage Five of tumble polishing used a “pre-polish” tin oxide powder of five micron size. Stage Six uses a “pro-polish” tin oxide powder of one micron size. In general terms, I am following the instructions provided by Colin Simmons of the Rotorua Rock and Gemstone Shop from whom I bought my tumblers. He also sells the two grades of tin oxide powder. Colin recommends that the Pro-Polish tumble should be for at least seven days, and he states that the pro-polish mixture is retainable and reusable for about six batches of tumbling as long as it does not become contaminated. In this instance, I used a pro-polish mix that I had used five times before.

The procedure for starting the Pro-Polish tumble is the same as for the Pre-Polish stage, using the key ingredients: the 4lb tumbler, the white pro-polish tin oxide powder, a plastic shaker with a tight lid, and the plastic beads kept for pro-polish tumbling (see the relevant previous Post for details):

I try to tumble a pro-polish batch for at least 10 days, even though Colin Simmons states that it is okay to tumble for only seven days (as the minimum). In this case, I had taken on a temporary job which kept me busy while the stones were tumbling and I left them for a total of 14 days and five hours before taking the barrel off the machine. The process of taking the stones out of the barrel and washing them is the same as detailed for the Pre-Polish Stage:

I then use my pro-polish toothbrush to finish cleaning the barrel before the next stage:  

However, instead of then putting the stones in a soap tumble, they undergo a longer tumble wash in borax as a burnishing process, which is Stage Seven, described in the next Post in this series.

“What Do I Need to Start Tumble Polishing Stones Myself? And What Will It Cost Me?” Part Two of a Two Part Post

This is a continuation from Part One.

6) POLISH POWDER – TIN OXIDE

In order to develop the polish or shine on a stone, the stages of smoothing using grit need to be followed up with one or two tumbles with polish. There are a number of different materials that can be used for polishing. These tend to be much more expensive than grit but can be reused for a number of tumbles. I use two grades of tin oxide because that is what was recommended to me when I bought my first tumbler, it is easily available for purchase, and it does the job very well for me. The first type is called “pre-polish” (a 5 micron size white powder) and can be purchased in the following lots – 250 grams for NZ$10.40, 500 grams for NZ$18.25 and 1 kg for NZ$32.00. The second type is called “pro-polish” (a 1 micron size white powder) and can be purchased in the following lots – 250 grams for NZ$18.00, 500 grams for NZ$33.55 and 1 kg for NZ$62.50.

Colin Simmons recommends that 7 tablespoons of pre-polish and pro-polish be used for each 3lb barrel load and 9 tablespoons for each 4 lb barrel load (I have followed these suggestions in my own tumbling). I don’t know how many tablespoons there are in the various containers of polish powder but it is suggested that each mix can be re-used up to six times (because it takes longer to lose its effect, and it does not wear away the stones and thus get contaminated as grit does, though contamination can sometimes occur). 

SAY you buy 250 grams of pre-polish and 250 grams of pro-polish =  NZ$28.40 (plus postage)

TOTAL so far = NZ$494.15 (plus postage)

7) POLISH POWDER STORAGE AND TABLESPOON MEASURING, AND POLISH MIXING AND STORAGE

I store my polish powders in plastic containers with tight lids. I use the same type of 2.2 litre container that I use for 320 grit. I also have one measuring spoon per powder and keep it exclusively in the same container. Again you could simply use the same metal tablespoon as used for the grit as long as it is cleaned after each use, or dedicate a separate metal spoon for the polish powders.

The two polish powders need to be mixed with water before being put into the tumbler barrel with stones. For months I struggled to find a way of doing this without messes, leakages and spills. I also had difficulty finding a way to store mixtures after use in such a way that re-mixing could easily be done (as the powder settles at the bottom of the water after a while). The best solution I have come up with is a plastic shaker with a very tight lid. I again use a Sistema product, a 700 ml To Go Shaker, costing about NZ$8 each, as other shakers I tried of a similar cost tended to leak when shaken. 

SAY you buy two powder storage containers for NZ$14, two tablespoon measuring spoons for NZ$8, and two shakers for NZ$16 = NZ$38 

TOTAL so far = NZ$532.15 (plus postage)

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The two storage containers for pre-polish and pro-polish powders.
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The two shakers for the mixing and storage of pre-polish and pro-polish. Note how the tin oxide settles on the bottom of the containers. Excess water can be poured off before re-mixing and use.

8) PLASTIC BEADS, BEAD STORAGE AND SPOONS

Plastic beads (or pellets) are added to stones in tumblers to cushion loads (so the stones hit each other less to avoid chipping etc.), to top up batches to the 2/3 mark of the barrel if needed, and to carry the grit and polish to all parts of a stone. The amount needed per barrel varies on the number of stones used, and tends to be greater as you move through the various stages of tumbling. I usually put 1 to 2 tablespoons in a tumbler even if I have enough stones to fill it to the 2/3 mark. The beads are long-wearing and reusable. They are not worn away during the tumbling, but can be contaminated by the different grit grades. So you don’t need a lot per batch but it can be useful to keep separate the beads used for the different grits and polishes.

Colin Simmons sells plastic beads (pellets) in the following lots – 250 grams for NZ$9.00, 500 grams for NZ$15.45 and 1 kg for NZ$28.40. I store the beads used for the various stages in separate 1 litre containers that cost about NZ$2.50 each. I have two metal tablespoons for use with the beads – one set aside for the three grits and one for the two polishes. I use these to ladle the beads from the storage container to the barrel, and to ladle the used beads from the sieve back to the storage container after each load. They live in two glass jars.

SAY you buy 1 kg of plastic beads for NZ$28.40 (plus postage), five 1 litre bead storage containers (NZ$12.00) and two metal tablespoons (NZ$3.00) = NZ$43.40 (plus postage)

TOTAL so far = NZ$575.55 (plus postage)

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Beads for different Stages in their separate containers.

9) SOAP FOR CLEANING AND BURNISHING

It is a good idea to do a soap tumble for between two hours and one day after each tumble stage. This gets rid of any minute amounts of slurry or grit or polish from the stones and barrel. The test of the effectiveness of this is the dirty colour of the water afterwards. The type of soap that should be used should be mild, non-perfumed and as pure (free of additives) as possible. I use sunlight soap (as I saw it was sometimes recommended by tumblers) – I buy three bars (I think it is) for NZ$4.00. I grate the bars and store the soap in a plastic container, adding just a few gratings to a washed batch of stones after each tumble.

After the final pro-polish tumble, it is recommended by many that a “burnishing” tumble be done which will make the stones just that little more shinier. My experience has proved this correct. I read somewhere sometime that someone used borax soap to do this, with good results. Borax can be hard to find – I use this  product, priced at NZ$10.90 for 1 kg. I add about 1 1/2 to 2 tablespoons in a 3lb barrel and tumble for at least 7 days.

SAY you buy sunlight soap (NZ$4.00) and borax (NZ$10.90), and a small plastic container for sunlight soap gratings (NZ$2.50) = NZ$17.40

TOTAL so far = NZ$592.95 (plus postage)

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Container of grated Sunlight soap and two whole bars as well.

10) SIEVES AND BUCKETS

In order to wash a batch of stones and beads after each tumble, I use a stainless steel sieve, with a larger plastic colander beneath it (the one I have is like this but was less expensive, or you could use one like this), with a plastic bucket under them. I run water over the stones and beads to clean them and wash the slurry off them. The stainless steel sieve retains the stones and beads as the water runs over and through them, the larger plastic colander acts as a safety net in case stones or beads get washed out of the stainless steel sieve (so they are easily retrievable), and the bucket holds the slurry to be disposed of safely afterwards.

I often use a second bucket to place the sieves on while I dispose of the slurry in a slurry storage bucket, wash out the original bucket, then place the sieves back on the original bucket to wash the stones and beads again – the resulting water is not very dirty and can be disposed of on the ground outside or elsewhere, keeping the level in the slurry storage buckets to a minimum. I would recommend that you use at least two stainless steel sieves, one for the grits and one for the polishes, with thorough cleaning in-between tumbles. However, to avoid contamination across grits, I have a stainless steel sieve for each grit grade and polish powder. 

SAY you buy two stainless steel sieves (NZ$10.00), one plastic colander (NZ$10.00), and two 10 litre plastic buckets (NZ$10.00) = NZ$30.00

TOTAL so far = NZ$622.95 (plus postage)

DSC02125
Stainless steel sieves for each Stage of tumbling.
DSC02124
My larger plastic colander.

11) MISCELLANEOUS USEFUL ITEMS

First, a “tumbling log” is important, even if it is only a piece of paper kept near your tumbler. You need to write down for each batch of stones you tumble things like: where the stones came from, the grit or polish grade used, when tumbling started (so you know when to stop), and anything unusual about the batch.  Secondly, I use paper towels a lot, to dry stones, clean barrels, wipe down surfaces and so on. If a cloth were used, there is the problem of potential contamination. Thirdly, I use old toothbrushes to clean the parts of the barrels that the lid rests on, to help ensure a clean fit – I have one toothbrush per grit and polish (five toothbrushes in all) and keep them in a glass jar. Fourthly, I use a permanent marker pen to write things on storage jars etc, so I know what is in them.   

SAY you buy paper towels (NZ$5.00) and a marker pen (NZ$3.50) = NZ$8.50

GRAND TOTAL = NZ$631.45 (plus postage if buy tumbler, grit, polish and beads online)

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Glass jars for spoons for beads and old toothbrushes for cleaning barrels – for grit on the left, for polish on the right.

Main Sources:

My own experience.

Lortone, 2011. “Professional Gemstone Tumbling.” 21 page booklet that comes with tumblers.

Colin Simmons. “Tumbling Procedure for Stone.” 2 page sheet.

Steve Hart, 2013. “Modern Rock Tumbling.” 96 page book.

Shelby Raymond, 2008. “Rock Tumbling for the Beginner”. 

“What Do I Need to Start Tumble Polishing Stones Myself? And What Will It Cost Me?” Part One of a Two Part Post

Occasionally I get asked these questions by someone who is considering polishing their own stones. The answer is not simple. The following account aims to be fairly thorough and realistic. Another of my key considerations is the use of equipment and processes to avoid the cross-contamination of tumble grits which can spoil the polishing process. As a tumbler manufacturer puts it, “Contamination is the primary reason for inferior results” (from Lortone’s booklet, “Professional Gemstone Tumbling”).  Keep in mind, too, that some of the things bought at the beginning will be useful for many weeks, if not months or years.

This is my attempt to set out what a beginning tumble polisher needs and how much it will cost (the costs reflect that I live in New Zealand):

1) TUMBLER

First of all, a tumbler is needed. My tumblers are of the “rotary” type by Lortone (a US manufacturer) and I have found them to be excellent. There are not many others available in our part of the world. The New Zealand Lortone dealer is the Rotorua Rock and Gemstone Shop (1120 Eruera Street, Rotorua, owned by Colin and Bev Simmons) which has a selection of tumbler sizes for sale. The smallest size is Model 3A, a single 3lb barrel, also the cheapest (currently NZ$249). About 45 to 55 small stones (up to about 2.5 to 3 cms each in size) will fit into one of these barrels. Larger barrels are needed for larger stones.

However, the best first buy is actually Model 33B, a machine which runs two 3lb barrels, currently costing NZ$370.75. As there can be up to five or six stages of tumbling, taking about five to six weeks in all, to polish one batch of stones, having two barrels makes the process twice as fast. It is important to avoid contamination of grit sizes from one tumble to the next so the barrels need to be cleaned carefully in between batches. (I have five different barrels, each dedicated to one grit size, but there is no problem reusing the same barrel for different grits if attention is paid to cleaning.)

The next largest barrel is a 4lb one, Lortone Model 45C, currently selling for NZ$359.50. Stones up to 4 cms big can be polished in this barrel, and it can take about twice as many stones as a 3lb barrel. I also bought one of these a few weeks after starting tumbling because I wanted to polish larger stones than the 3lb barrel could, and it also allows me to tumble more stones at a time. I have no personal experience with any other tumblers.

SAY you buy one Model 33B Lortone tumbler = NZ$370.75 (plus postage if buying online)

DSC02111
Two Lortone 33B Models in the shed, one is mine and one is my wife’s. The motor and frame for a Lortone 45C Model sits to the left. The tumblers sit on plastic trays. Each tumbler is labelled with the Stage it is used for. There is a power point to the left, outside the photo.

2) SITING OF TUMBLER

Secondly, a place to site the tumbler is needed. The following are the main considerations: NOISE – The Lortone tumblers are powered by small electric motors (designed to run 24/7) which are very quiet. When barrels containing stones, water and grit are tumbling, there is also very little noise (less than slowly moving stones in water in a plastic container by moving the container from side to side). I first ran my tumbler in the garage which is attached to my house. It was only just possible to hear a vague noise in the background when in the house. Any other noise will be greater. However, the tumbler operates 24 hours a day, including at night.

After a couple of weeks or so, I moved the tumbler to a shed outside, mainly to have more space. One consideration affecting noise is what the tumbler rests on. A little heat is generated by the electric motor so I decided not to place it on newspaper or any kind of soft material, which would also be noise absorbing. My tumblers sit on a plastic tray which seems to deal with the heat issue fine, but it probably does not minimise the noise of tumbling (but it’s actually very low anyway, and my tumblers are out in a shed). I also initially chose a plastic tray to contain any spilled water but this has never been a problem (the lids on Lortone tumblers are very effective, mine have never leaked and have never blown off).

FLAT AREA FOR TUMBLER – An area at least the size of the tray the tumbler rests on is required.

SOURCE OF ELECTRIC POWER – Needs to be within reach of a power point (though extension cords can be used, of course).

NEAR TO WATER – Water is used a lot in tumbling – it goes in each tumbling barrel and is needed to wash stones coming out of a barrel. Having a water tap within three or four metres of the tumbler is a good idea.

NEAR A FLAT WORK SURFACE – This is needed when sorting stones, filling barrels, emptying barrels, and so on. In my view a minimum of 1 metre by 1 metre at waist height is needed. 

NEAR TO STORAGE – Stones, grit, and sieves are among the things that need to be stored or at hand. At least a couple of shelves would do, or a further flat surface such as a table or desk.

DSC02130
We installed a tap and sink in the shed where the tumblers are. Note the flat surface to the left of the sink, where tumblers are loaded and emptied.
DSC02112
Just part of the storage space we have. The top shelf includes barrels not currently in use. The containers on both shelves have stones from different places as well as stones at different stages of tumbling.

3) TUMBLING GRIT – SILICON CARBIDE

Silicon carbide grit of various grades is used in the tumbling barrel to shape and smooth the stones, and needs to be purchased. Usually two or three different grades are used, depending how smooth the stones are at the beginning of the process. Different tumbling practitioners and tumbler manufacturers use or recommend different stages and/or grit sizes (see, for example, Shelby Raymond’s “Rock Tumbling for the Beginner” which uses different grit grades than what I go on to recommend). The following is what I use, based on the recommendations of Colin Simmons (Rotorua Rock and Gemstone Shop) as he sold me my first tumbler, he stocks this grit for sale, and they work well for me. However, remember that variations are not uncommon (different grit sizes).

The coarsest grit I use is 100 grade – this is good if the stones need some rounding or if they have cracks and pits that need removing. I next use 220 grade to increase the smoothness of the stone – many of the stones I collect are off beaches and they are often very rounded and smooth to begin with, so these can be started with 220 grit, or even 320 grit, skipping the 100 grit stage. Then I use 320 grade grit for the final smoothing.

Colin Simmons in Rotorua currently has 100 grit for sale in 500 grams size (NZ$13.20), 1 kg size (NZ$18.70) and 2 kg size (NZ$36.80). He sells 220 grit for the same prices – 500 grams size for NZ$13.20, 1 kg size for NZ$18.70 and 2 kg size for NZ$36.80. He sells 500 grams of 320 grade grit for NZ$16.40, 1 kg for NZ$20.60 and 2 kg for NZ$40.80. Lortone recommend that 4 tablespoons of grit be used for each 3lb barrel load and 6-8 tablespoons for each 4 lb barrel load (I generally follow these suggestions, using 7 tablespoons for my 4 lb barrel loads). I have just measured the number of tablespoons there are in a 2 kg lot of 100 grit (as it was the only unopened grit I had) – there are 90 (and I tried to make each tablespoonful an even one), and thus there is likely to be 45 tablespoons of grit in 1 kg of 100 grit. I suspect there would not be much difference for the 220 and 320 grits (give or take 3 or 4 spoonfuls maybe). This means 1 kg of grit contains enough for about 11 barrels.

In my view, given that someone makes the initial financial investment in a tumble barrel, it would be worth getting 1 kg of each grit to start off with (it is cheaper than the 500 grams size and there is little to be saved in buying 2 kgs, except maybe postage). 

SAY you buy 1 kg each of 100, 220 and 320 silicon carbide grit = NZ$58.00 (plus postage, if buying online) 

TOTAL so far = NZ$428.75 (plus postage)

4) GRIT STORAGE AND TABLESPOON MEASURING 

The grits as sold by Colin Simmons come in plastic containers of the kind used for milk in New Zealand. This means the openings are so small that it is impossible to insert a measuring spoon. Pouring the grit out for each batch of stones may not be a good idea because of the risk of spillage. I therefore store my grit in containers that I can easily reach into with a spoon. I tend to buy Sistema plastic storage containers generally because they are good quality and have effective lids. Often they can be bought on sale. I use a 2.4 litre container for both 100 and 220 grit and a 2.2 litre container for 320 grit (this has a stronger set of clips as I wanted greater security for the finer powder). However, any container with a lid will do.

In order to avoid cross-contamination of grits, I strongly suggest you buy one measuring spoon per grit size and keep it exclusively in the container with that grit (you might have to buy three sets of cheap plastic measuring spoons if separate tablespoon measures are not sold). Alternatively, one metal tablespoon could be used as long as it is cleaned after each use.

SAY you buy three containers for NZ$20 and three tablespoon measuring spoons for NZ$12 = NZ$32 

TOTAL so far = NZ$460.75 (plus postage)

DSC02116
The middle shelf here contains the grit containers. The top shelf has the polish powders and plastic beads.
DSC02119
The three grit containers. Note the white measuring spoon in each.

NOTE: You can get a sense of all the elements and equipment involved in tumbling a batch of stones in this post describing the details of the various stages in doing a 100 grit tumble.

5) MEANS FOR DISPOSAL OF SLURRY

You need a means for disposing or storing the slurry that results from tumbling. This slurry consists of water and broken down grit and tiny rock fragments (it would be a fine dust if it was not wet). This slurry should never be put down a household drain as it will settle into traps, turn into concrete and ruin the plumbing. I pour it into a bucket. I then pour the water off the top of the bucket as the sediment settles, a nuber of days later. A fine sediment builds up a number of layers after a number of slurries are poured into the bucket. The sediment can be disposed of in a hole dug outside, or in the household rubbish collection etc. I have a number of buckets next to my water tap for this purpose.

DSC02123
Buckets used for slurry.

When we installed the sink in my shed, we attached it directly to a hose which runs a few metres out onto the ground – this means we are able to wash minor amounts of slurry down the sink drain without it blocking anything. (It’s also a good idea to avoid getting any slurry or grit, which is silicon carbide, onto clothes or towels etc. which are then washed in a washing machine as the slurry and grit can damage the machine and drains.) 

SAY you buy one 10 litre plastic bucket for NZ$5 

TOTAL so far = NZ$465.75 (plus postage)

Continued in Part Two.

The Seven Stages in Tumble Polishing Stones: Stage Four, 320 Grit Tumble, 10-20 March 2018

There are seven stages in the tumble polishing of stones. The first stage is acquiring the rough stones. Stage Two involves tumbling rough stones in a solution of water and 100 grade silicon carbide abrasive grit. Stage Three entails tumbling the now smooth stones in 220 grade grit. The 40 Riverton stones being tumbled for this series of Posts were next placed in 320 grade grit, Stage Four, on 10 March after I had returned from my South Island stone collecting trip. This Post is the sixth in this series, the first Post being here.

Note that in this series I have counted the collection of stones as Stage One. Nearly all other accounts of tumble polishing call the first actual tumble Stage One whereas I have called it Stage Two – and this affects the numbering of all subsequent Stages.

Furthermore, while I initially put nearly all the stones I collected through Stages Two, Three and Four, I no longer do this as a matter of course. More often these days, I consider starting a stone at Stage Four, some of them I start at Stage Three, and I rarely start a stone at Stage Two. This is because I mainly collect smooth beach stones that do not need shaping and/or smoothing as much as stones found in rivers or on dry land.  

So, for Stage Four, I place the 40 Riverton stones in the 4lb tumbling barrel. Water, plastic beads, and 320 grit are then added. I use about 16 tablespoons of beads to bring the load level up to about two-thirds, as the stones have gotten smaller with each tumble. I don’t usually put just the same load of stones through each stage – I usually do two or more loads at the lower grit grade and then sort each load in relation to which Stage they should go to next. In this way I am able to collect enough stones for a good-sized load for each stage.

I use a number of compartmented plastic trays, 45 cms long, 30 cms wide and 8 cms deep, for sorting and storing stones in order to collect enough for a tumble load.

Back to the Riverton stones being tumbled for this series on the Stages of tumbling: 

As with Stages Two and Three, I add water and seven tablespoons of grit (320 grade) to the barrel for Stage Four. I then tumble these stones for nearly 10 days. The recommended time for Stages Two, Three and Four is seven days each but this is a minimum and I often leave the tumbler going for another three or four days per stage.

So, after nearly 11 days tumbling, I empty the tumbler into a stainless steel strainer (sieve) labelled for 320 – it is used only for stones straight after being tumbled in 320 grit (to prevent contamination with other grades of grit). 

004
Sieves for the different grit and polish grades

The strainer is placed over a bucket and I run water over the beads and stones to wash the slurry away. I then clean the empty barrel, using a toothbrush labelled for “320” use, also using a paper towel (as previously described in detail for Stage Two).

After thorough washing, I put the stones back in the barrel. I add water along with a few flakes of sunlight soap and place the barrel back on the tumbler. In this case, for these 40 stones, I tumble them in soap for just over three days. Sometimes I run a soap tumble for only a day, but as I am going to re-use the 4lb barrel for the next stage, pre-polishing, I want it to be as clean as possible to avoid contamination with previous grit. 

So on Friday morning, 23 March, I empty the soap-tumbled stones out of the barrel and wash them and the barrel.

aa1
Taking the lid off the 320 grit tumble.
aa2
Washing the stones after the 320 soap tumble.
aa3
The 40 Riverston stones fresh out of the soap tumble folloing the 320 grit tumble.
aa4
The amount of plastic beads used with the 320 tumble.
aa5
The water from the post-320 soap tumble – significant additional slurry is removed from the stones and barrel.

Once the stones are dry I put them on the scales and discover they weigh 1261 grams.

aa6

At the start, before any tumbling, the stones weighed 1605 grams, losing 8.4% of that weight during the 100 tumble (ending up weighing 1470 grams after the 100 stage). During the 220 grit tumble, 9.3% of this 1470 grams was lost (the stones ending up weighing 1353 grams). Stage Four, the 320 grit tumble, resulted in a reduction of a further 92 grams, which is 6.8% of 1353 grams. In total, through Stages Two, Three and Four, the stones have lost 344 grams of their original weight of 1605 grams, which is 21.4%, just over one-fifth.  

The amount of material lost during tumbling is dependent on a number of factors – the length of tumbling, the softness of the stones, any chips lost from the stones, and so on. 

The next Post is about the state of the stones after the 320 grit tumble.

The Seven Stages in Tumble Polishing Stones: Stage Two, 100 Grit Tumble, 15-25 November 2017

There are seven stages in the tumble polishing of stones. The first stage is acquiring the rough stones, the topic of The Seven Stages in Tumble Polishing Stones: Stage One, Stone Collection, Riverton, 2-6 November 2017. The stones to be tumbled as illustrations in this series are described in The Seven Stages in Tumble Polishing Stones: The Selected 40 Stones. Stage Two involves tumbling rough stones in a solution of water and a low grade abrasive grit, in this case, 100 grade silicon carbide. (Note that if a beach stone is quite smooth, this stage, and even the next one, could be skipped. If a stone is quite rough or jagged or has pits in it, it might need to go through this stage twice.) A 4lb tumbling barrel will be used as the largest stones are too big for the smaller 3lb barrel.

Note that in this series I have counted the collection of stones as Stage One. Nearly all other accounts of tumble polishing call the 100 grit tumble (or the tumble with some other coarse grade grit) Stage One whereas I have called it Stage Two – and this affects the numbering of all subsequent Stages.

First, the stones are placed in the 4lb rubber barrel and plastic beads (also known as pellets) are added. The beads help to “carry” the grit to the surfaces of the stones, making the process more efficient and thorough. When not enough stones are available to make a good-sized load, beads are also used to bring the contents of the barrel up to two-thirds full, the ideal level of good tumbling (see this video for a demonstration of why two-thirds is a good level). These beads were bought from my stone tumbling supplier in Rotorua. Once beads are used with a particular grade of grit, they are stored in a marked container and used only with the same grit – this prevents contamination of one kind of grit by another (each grade of grit produces a consistent set of minute scratches on the stones, contributing to the final polished product). I have a kitchen dessert spoon that I use for 100, 220 and 320 grit beads, and another is used for the pre-polish and pro-polish beads, again to minimise cross-contamination. I added 10 dessert spoons of beads to the barrel, then added water to just above the level of the stones and beads.  

b - 4lb barrel
About to add beads to 4lb barrel
c - 4lb barrel with beads
Barrel is 2/3 full of stones and beads
d - 4lb barrel with beads and water
Water is added, to just above the level of the stones

Silicon carbide grit is added next. I use seven tablespoons of 100 grade grit for a 4lb barrel load (the guidelines are “6 to 8 tablespoons”). I keep different grades of grit in their own containers, and each container has its own tablespoon measuring spoon (to avoid cross-contamination):

e - 4lb barrel and 100 grit container
About to add 100 grade silicon carbide grit
f - 100 grit
A measuring spoon is kept in each grit container
g - 100 grit being added
The grit is added to the mix of stones, beads and water
h - 100 grit being added 222
Seven tablespoons of grit have been added

The lid is then placed on the barrel and the barrel placed on the tumbler. It will now rotate continuously on the tumbler for at least seven days (the recommended time). Longer is fine – I often tumble for about two or three days more. The grit breaks down after a while, but then it can act like a finer grit.

i - top on barrel
It is important not to over-tighten the lid
j - barrel ready
The barrel ready to be placed on the tumbler
k - tumbler motor
A small electric motor turns one of the rods
l - barrel on tumbler
The barrel rotates at a slow and steady rate. The electric motor is very quiet. As the barrel is rubber, there is little noise made by the tumbling

Finally, I fill out the Tumble Log, noting where the stones are from, the type of barrel and grit used, how many beads or pellets were put in, the time and day the tumbler was started, how much grit was used, and the weight of the stones. This is my 189th barrel since I placed the first one on the tumbler in March 2016.

m - tumbling log entry
I developed this simple log myself and print off pages as needed

Nine days later, on Friday 24 November, I turn the tumbler off and prepare to open the barrel to see how the stones have fared. I grab a yellow plastic colander that hangs on the wall under a calendar and then select the appropriate stainless strainer from nearby, one labelled for 100 grit. There is a strainer dedicated to each grade of grit and polish, to avoid cross-contamination. I place a bucket in the sink then put the colander and strainer across the top. I will pour the stones and beads into the strainer, to wash them, and the colander will act as a safety net in case some spill over the side of the strainer. I also have some paper towels handy for cleaning and mopping up purposes.

n1 collander
Plastic colander, which is placed under a strainer whenever barrels are emptied and stones washed, to act as a safety catcher
n2 strainers
Bottom left is 100 grit stainless steel strainer, bottom right is 220 grit strainer. Top strainers are for 320 grit, pro-polish, and pre-polish. Small strainer at bottom, far right, is a spare one, sometimes used for scooping up beads that have fallen into the bucket
n5 work station
Work station around the tap and sink, built by my wife Petra (who also tumble polishes stones). Paper towels are used for cleaning and mopping up
n6 prep1
After tumbling, the contents of the barrels are poured into a strainer resting on the colander, placed over a bucket. This allows slurry to be disposed of appropriately

I carry the 4lb barrel over to the sink and take the top off. Inside what is first apparent is the grey liquid slurry that contains the material that the grit has worn away from the stones. Some broken down grit will also be part of this mix. I hold the lid under the stream of water from the tap so that the slurry and beads on the lid are washed into the strainer. I then use a paper towel to wipe the lid, especially the outer rim which is the connection to the barrel’s rim – when the lid is placed back on the barrel, this connection needs to be clean so that the seal is a good one. No matter how much water is run on the lid to clean it, a paper towel will always pick up more.

n7 lid off
After a few days tumbling, the water in the barrel contains a grey slurry of very fine material worn away from the stones.  Sometimes there may also be a little foam
n7 wash lid
Rinsing off the lid, holding it so that any beads are washed into the strainer
n8 lid wipe
Wiping the lid after the rinse will remove any remaining slurry and/or broken down silicon carbide

The contents of the barrel are then poured carefully into the strainer, usually with water running to assist the clearing and cleaning process. The beads and stone are covered in the grey slurry, and at the bottom of the barrel will be a muddy sticky layer where the slurry has started to settle in the short time it has stopped tumbling. Some of the smaller stones are likely to get stuck in this and extra water will be needed to free them. We reach the point where the stones are relatively clean and 99% of the grey slurry has been washed through into the bucket beneath. 

n9 slurry pour1
Pouring the barrel’s contents into the strainer
n10 slurry pour2
The stones are covered with the slurry
n12 slurry pour4
There is usually some slurry that has settled at the bottom of the barrel, and water may need to be run into it to remove the last stones and beads
n13 slurry rinse
Once all the stones and beads are in the strainer, some water is run over them to wash away the slurry covering them
n14 slurry rinse2
The stones and beads after the initial rinse

The next steps are to empty the slurry, clean the barrel, and do a final rinse of the stones before putting them back into the barrel for a soapy tumble.

The slurry in the red bucket in the sink is poured into a bucket on the floor. There, over the next few days, the slurry will settle. The water on top can eventually be poured off and the accumulated sediment in the bucket will be buried or otherwise disposed of. Slurry should never be poured down the drain in a house as the sediment will accumulate in the S-bend, turn as hard as concrete, and block the pipe. Once the slurry has been poured out of the red bucket, it will need rinsing. The sink in my shed has no S-bend, drains through a hose out onto the ground a few metres away, so sending some slurry down it is ok.

n15 slurry
The slurry in the bucket after the first wash of stones
n16 slurry pour
Pouring the slurry into settling buckets on the floor
n17 bucket after slurry pour
The bucket needs to be rinsed, and sometimes wiped, to get rid of the slurry remnants

The 4lb tumbler barrel needs to be well washed out. Then attention needs to be given to the rim of the barrel, where the lid “seats” and seals. Stubborn slurry needs to be removed. I use a toothbrush for this, and have a brush for each grade of grit and polish (with the grade written on each). Finally I wipe the rim down with a paper towel.

n19 brushes
I keep three toothbrushes in a jar, to clean the barrels. The spoon is to move the washed beads from the strainer
n20 barrel clean1
Each toothbrush has the grade of grit written on it to avoid cross-contamination
n21 barrel clean2
Using the toothbrush to clean slurry and grit from the rim of the barrel
n22 barrel clean3
A final clean of the rim with a paper towel

The stones and beads in the strainer are then given a thorough rinse, to remove as much slurry from them as possible. After that, I place the stones then the beads back in the 4lb barrel, topping them up with some more beads (as the size of the stones has been reduced due to the previous nine days of tumbling and it is a good idea to refill the barrel to two-thirds). Water is added to the level of the top of the stones, and a little soap is sprinkled on top. I have seen various sources recommend the use of a mild low-sudsing soap, with Sunlight mentioned. I have managed to track down an outlet for Sunlight soap and I grate the cakes. The lid is then placed on the barrel and it is put on the tumbler for a few hours. This cleans the last of the slurry off the stones, and also cleans the inside of the barrel.

n18 final rinse
Final rinse of the stones and beads
n23 replace in barrel1
The washed stones are placed in the barrel again for a soap tumble
n24 replace in barrel2
The beads are also rinsed
n25 replace in barrel3
Using the spoon to put the rinsed beads back in the barrel
n26 bead topup
Topping up the barrel with other beads that have previously been used for 100 grit tumbling
n27 soap1
Grated sunlight soap is stored nearby
n28 soap2
Just a few gratings are added then the lid is put on and the barrel placed back on the tumbler

The two last jobs for this phase is to clean the bucket (it contains the remnants from the final rinse of the stones) and to add details to the Tumbler Log about the time the tumbling ended, how long the tumble period was, and to note when the soap tumble started.

n29 bucket after rinse and remove
This is the water in the bucket after the stones and beads have had their second rinse.
n30 log update
Adding details to the Tumbling Log

After 12 hours, I take the barrel off the tumbler to remove the stones and beads from the soapy water. They are placed in the strainer again and rinsed. The stones are placed on a paper towel. I remove as much water from the beads as I can then they are spooned into the “100 grit” storage container.

n31 after soap1
Not a lot of soap is needed for an effective wash
n32 after soap2
Using the colander and strainer to rinse the soapy stones
n34 after soap4
This is the result of the 12 hour soapy tumble – a significant amount of extra slurry is removed
n33 after soap3
The washed stones are taken from the strainer and placed on a paper towel

When I weighed the dry stones, I found they were now 1470 grams, having lost 135 grams during the tumbling process. This means they lost 8.4% of their weight. In my experience, this is towards the lower end of the expected range, meaning that perhaps at least some of the 40 stones being tumbled are relatively hard. I add the end weight to the Tumbling Log.

n35 weigh after 100
Weighing the dry stones after the 100 grit tumble

n36 final log

The last thing to be done before the stones go to the next tumbling stage is to “sort” them. This means that I look at each stone in good light while it is dry. I look for lack of smoothness and consider whether a stone would benefit from more tumbling in 100 grit. A relatively small imperfection in smoothness is ok as the 220 grit tumble will remove that. In rare cases I will decide that a stone can skip the 220 grit stage and move straight to the 320 grit tumble. Sometimes, especially after the finer grit tumbling, I use a loupe (magnifying glass) to check for cracks, pits and imperfections before deciding what to do with a stone. This loupe can magnify three times (the magnification I used most often) or six times or nine times.

n37 sorting
My sorting tray for Riverton stones
n38 magnifier
My loupe, or magnifying glass – it has three x3 lenses that can be “overlapped” to increase magnification

The next Post considers the inspection and sorting of the stones prior to them being tumbled in 220 grade silicon carbide grit. 

The Seven Stages in Tumble Polishing Stones: The Selected 40 Stones

The first Post in this series described Stage One, Stone Collection. To illustrate the next six stages in the tumble polishing of stones, I decided to select 40 of the stones I had collected at Riverton in early November. I chose a range of sizes, colour and quality. The following are photos of all 40 stones, first of all how they appear dry and then how they appear wet. This demonstrates how wetness brings out colours and patterns much better.

Stones 1 to 5:

1st 4 dry1st 4 wet

It will be interesting to see how much of each stone is worn away throughout the tumbling process. Stone 1 (far left) is about 8 cms long and about 5 cms wide at its widest point (using the graph paper it is lying on in the “dry” pic above).  Stone 3 is about 6 cms long and 4.5 cms wide, while Stone 5 (far right) is just over 7 cms long and is 3 cms wide. I think that Stone 1 is of volcanic origin, as it has small specks in it that would have originally be gaseous pockets, and will turn out to be similar to another Riverton stone I polished recently (below). 

DSC07257

Stone 2 is also probably volcanic in origin, having similar specks. Stone 4 looks like a conglomerate (which simply means it consists of small rounded stones cemented together in a fine-grained matrix). [As its surface became clearer after some tumbling, I decided Stone 4 is in fact a breccia, composed of angular fragments.] Stones 1, 2, 4 and 5 would be too big for a 3lb barrel.

Stones 6 to 10:

2nd 4 dry2nd 4 wet

These are progressively smaller, with Stone 6 (far left) being about 6 cms long and 4 cms wide. Stone 7 could be argillite (a kind of mudstone subjected to heat and pressure) or epidote (green coloured rock), Stone 9 is a breccia (which simply means it consists of broken fragments of very small stones) and Stone 10 is another conglomerate. 

Stones 11 to 15:

3rd 4 dry3rd 4 wet

The progression to smaller continues. Stone 14 (second from right) is a pink granite that is just over 5 cms long and is just under 4 cms wide at the top. Stone 12, a quartzite, demonstrates how wetness brings out the nature of a stone. Dry, it appears a bland white. Wet, patterns of colour in a strand-like formation become visible with a subtle depth being present. Stone 15, which could be argillite, has an interesting wavy band of white silica.  

Stones 16 to 20:

4th 4 dry4th 4 wet

Stones 18 and 19, both about 4 cms long, are potentially quite spectacular. Stone 18 has a number of different coloured bands. Stone 19 contains contrasting black and white sections, and it will be interesting to see if these erode or polish differently.

Stones 21 to 25:

5th 4 dry5th 4 wet

Stone 25 (far right) has some interesting bands that will be brought out by the tumble polishing, but Stone 22 (second from left) may turn out to be even more interesting. The white on the surface of Stone 23 (middle) may be worn away in the process it goes through, but there may be interesting patterns underneath.

Stones 26 to 30:

6th 4 dry6th 4 wet

Stone 26 (far left) is 3.5 cms long and just over 2.5 cms wide. Its two-toned character attracted my eye on the beach. White is a colour that always stands out on the beach too, Stone 27 being a white quartz with a couple of dark intrusions.

Stones 31 to 35:

7th 4 dry7th 4 wet

Stone 31 (left) may be part-jasper, and Stones 32 and 34 are probably varieties of jasper. Stone 33 has interesting reddish protuberance that caught my eye on the beach. Stone 35, white quartz, is 3 cms long and just under 2 cms wide. 

Stones 36 to 40:

8th 4 dry8th 4 wet

The smallest stone, Stone 40 (far right), jasper, is 2 cms by 1.5 cms. Up to 20% of a stone may be worn away by the tumbling process so not much may be left of this at the end. However, small stones are good in a tumbling barrel as they “carry” the grit and polish to the larger stones.   

I weighed the 40 stones on a set of scales I have in my stone tumbling shed. First placing the empty container on the scales, I moved the setting back to zero so that only the weight of the stones would be indicated = 1605 grams (3.5lbs).

a - weigh in

I will weigh the stones after each stage of tumbling to see how much of them is worn away. 

The next Post in this series describes Stage Two of tumble polishing, the 100 grit tumble.