Time management is an important part of tumble polishing. There exist guidelines for how long each stage should take, whether it be grit or polish or burnish. For example, it is generally recommended that you tumble stones for about a week in each size of grit. I have followed this approach in my series of Posts “The Seven Stages in Tumble Polishing Stones”. I keep a tumbling log for each batch of stones, recording the day and time it starts. That way, I can see when the week is up.
However, it is also advised that some stones may need more than a week in, say, 220 or 400 grit. I sort through the stones after each tumble and decide which ones are ready to go to the next stage, which ones need to repeat the stage, and maybe which ones would benefit from going back a stage.
It is difficult to be patient, to wait until the time is up. I try hard to add an extra day or so to the usual week for most stages, but don’t always succeed. Also, I have slipped into the practice of burnishing with borax for only two or three days instead of a full week. And I have been thinking everything has been going ok.
Two things have given me pause recently, have forced me to rethink my approach to timing. The first was a batch of stones that I noticed were polished better than usual. It was a group of Kakanui stones that had just finished polishing in a 3lb barrel. I was pleasantly surprised to see how shiny they were.
I checked in my tumbling log. They had spent 10 days in pro-polish and six days in borax. The extra time was because I had been busy doing other things. I don’t actually know for sure if the extra shininess of the stones is due to some quirk of my current perception, or the couple of extra days in pro-polish, or the longer than usual time in borax. The pro-polish mixture had been used three times before, so the cause was not fresh polish.
I am now more of a mind to give the polishing tumble stage a bit more time and to make sure the burnishing tumble in borax goes at least close to the full week.
The second thing that has caused me to rethink timing issues was when I was recently asked a question by email about the use of grits and polishes for a larger barrel than usual. After providing information about different grits, different barrels and tumbling times for different stages, I added something I remembered when I visited an older and experienced tumble polisher about four years ago. I wrote: “He said that sometimes he simply puts stones into coarse grit and tumbles them for a few weeks – his notion is that the grit breaks down, just as the stones do, and the grit gets finer as the process proceeds, and he ends up with smooth stones at the end.” I have come across this idea a couple of other times, and it was recently repeated in a conversation I had a couple of days ago with another tumble polisher. I may experiment with this approach myself one day but, in the meantime, I am certainly encouraged to give my barrels more time.
There are exceptions to every guideline. There is an interesting stone I find at Kakanui that comes from an ancient fossilised seabed – it is also known as fossil hash. It is kind of grainy, not smooth or shiny. l have discovered that after up to a week in 400 grit, it feels smooth and waxy. Any longer doesn’t improve it and starts to reduce it in size significantly. Polishing doesn’t improve the stone at all, so it is at its best after the 400 tumble.
In this case, less time tumbling is the right thing to do. But this is an exception.
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