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.

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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.
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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)

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The middle shelf here contains the grit containers. The top shelf has the polish powders and plastic beads.
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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.

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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.