(This is the fourth Post in this series, the first one being here.)
Stage Two in tumble polishing involves tumbling rough stones in 100 grade silicon carbide grit. Stage Three involves tumbling in 220 grade grit. In between these stages, and in between later stages, I inspect each dry stone in a good light to check that it is suitable to go on to the next stage. Sometimes it may need to repeat a stage, or it may become apparent that there is a reason to discard a stone entirely.
The following presents the 40 Riverton stones after the 100 grit stage then describes their inspection and sorting. This initial stage of tumbling has resulted in smoother stones, and their colour is now more apparent.
Stones 1 to 5, dry then wet:
Stones 6 to 10:
Stones 11 to 15:
Stones 16 to 20:
Stones 21 to 25:
Stones 26 to 30:
INSPECTING AND SORTING
I inspected each stone when it was dry. I sat under a bright light and simply held the stone and turned it around. I found that 22 of the 40 stones are nice and smooth with no chips, nicks or pits. Some of these could skip the next stage and go straight to being tumbled in 320 grit but for the sake of this series of Posts I will keep them with the others for tumbling in 220 grit.
Five stones (5,11,12,19 & 28) have very minor cracks, pits or slight gouges. Here are two examples: Stone 11 has a very minor superficial crack.
Stone 19 has a couple of very small superficial cracks as well, one of which is indicated below.
Such very minor “imperfections” are usually easily removed in the 220 grit tumble.
Eight stones (1,2,15,20,23,26,34 & 39) have small or medium-sized pits or cracks. These also usually disappear after tumbling in 220 grit. Three examples: Stone 1 has a number of small pits.
Stone 15 has a small gouge in the side.
Stone 20 has a small surface crack.
Three stones have issues that I would normally hesitate over for some time, considering whether to tumble them again in 100 grit. Stone 4 has a small indentation in its side.
Stone 25 has a number of noticeable cracks and pits in it. It is one of the smaller stones.
Another small stone, Stone 31, has some chips on it. It is easier to get rid of such chips if the stone is larger because it can stand up to losing another 5% or more by repeating the 100 grit tumble. But because it is so small, it can be worth trying the 220 grit tumble first to see if it improves without losing too much of its mass.
Finally, there are two stones that I would normally put back to another 100 grit tumble. Stone 9 has a medium-sized pit in its side.
Stone 10 has an even deeper hole in it from where a small embedded piece of stone has loosened and come out.
All 40 stones will be retained for the 220 grit tumble (Stage Three) so that we can monitor what happens to them – see The Seven Stages in Tumble Polishing Stones: Stage Three, 220 Grit Tumble, 4-13 December 2017.