NOTE: March 2021. Due to changes in the supply of grit and polish, plus a few other things, there are now six stages that I recommend instead of seven. The details are in UP-DATE OF “The Seven Stages in Tumble Polishing Stones” – One Less Stage. However, there are many useful practical suggestions in this original series so I have decided to leave it basically unchanged.
There are seven stages in the tumble polishing of stones. The first stage is acquiring the rough stones, stones of the right shape and condition and colour that show good promise for polishing. (Note that nearly all other accounts of tumble polishing don’t include stone collection as a stage.) Stage Two, for me, 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. In Stage Three I repeat this process, using 220 mesh silicon carbide grit, while Stage Four is the same procedure with 320 silicon carbide grit. At this point, the stones should be shaped and smooth enough to begin actual polishing. I then use two polishing stages. 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. The final stage, Stage Seven, is a “burnishing” tumble for a week in borax. At every stage, stones are individually examined and may be set aside to repeat a stage or, more rarely, even skip a stage.
I emphasise that these seven stages describe what I normally do. However, I often start tumbling a newly collected smooth beach stone at Stage Four. Note that other tumble polishers often use different grits and polishes in different ways. What I am describing is what I do and how I do it.
For me, Stage One, stone collection, usually involves spending time on beaches, head down, occasionally bending over to pick up a stone worthy of collection. The best way to decide if a stone is worth polishing is to view it wet, so I often walk along the sea edge where the waves roll in then die out as they wash over the sand and stones. I will often take a promising dry stone to the wave edge so it can be wettened to bring out its colour. If it is raining, all the better as I then do not need to keep on checking for the next big wave that may wash in and wet my feet.
I often wear gumboots but sometimes even those are overwhelmed by an unexpectedly larger or more energetic wave.
Clothes worn for stone collecting: usually warm clothes as beaches are often windy; gumboots or jandals depending on temperature; cap (if sunny) or woolen hat (if cold and cloudy); light waterproof coat and waterproof over-trousers if weather is wet.
Equipment used for stone collecting: small backpack to carry drinking water, food, camera, plastic collecting bags, and collected stones.
Kinds of stones worth collecting: those with interesting colours and patterns; the smoother the better; the harder the better; the more slippery the better; with a minimum of cracks and pits and jagged edges; not too big (as the tumble barrels are small) and not too small (as the polishing process wears away a proportion of the stone). When wet, you can see a stone’s colours but the cracks and pits in it are not so easy to see. When dry, the cracks and pits can be more easily seen, but the stone will look dull.
I mainly collect beach stones and river stones. They have the advantage of being smoother and more easily identifiable than stones or rocks found anywhere else. They are easier to tumble polish because their jagged edges have already been worn off.
Some beaches have just a scattering of stones along the sand – it is still possible to find some very good specimens here as you stroll along.
Other beaches have masses of stones. Sometimes a collector need just stand or sit there to find many good specimens.
Stone collecting means that you visit interesting and scenic places. During this trip to Riverton, I appreciated patterns on the sand at Henderson Bay, bird wildlife at the Back Beach, and the rising of a full moon over Taramea Bay.
Once the stones are collected, they need to be taken home. Sometimes, such as when I am travelling by aeroplane, that means putting them in a plastic container and then posting them. When I went to post some to my home in the North Island at a Post Shop in Gore, I was asked by the assistant, “Don’t they have any stones up there?” “Not like these, no,” I replied, and I showed her some polished ones I had in my pocket. She was amazed at their beauty and understood why I was doing such a strange thing as mailing what looked like ordinary everyday stones across the country.
The next stage in tumble polishing happens at home after I unpack the collected stones or after the Postie has delivered those I earlier put in the mail. Stage Two involves tumbling rough stones in water and a low grade abrasive grit. In the next Post I will describe the Riverton stones selected to go through the stages of tumbling to illustrate this series. I will then look at their first tumble, in The Seven Stages in Tumble Polishing Stones: Stage Two, 100 Grit Tumble, 15-25 November 2017.
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