Tumble polishing fossilised worm cast stones has a different aim from polishing other stones because it is important to preserve the traces on the surfaces of the stones. Tumble polishing is normally a process involving the smoothing of a stone by wearing away its outer layer. Sharp edges, pits and nicks in a stone can be removed by tumbling in a coarse grit. But such a tumble for a worm cast stone may very well destroy what makes the stone interesting.
For this reason, I ignore any “imperfections” in the stone itself and seek solely to polish the trace. In order to do this, I tumble worm cast stones once in 320 grit, the finest (least coarse) grit that I normally use, before putting them through a pre-polish then pro-polish tumble. NOTE: (March 2021) Due to a change in the grit size sold by my supplier, I now use 400 grit.
The other day, a question arose in my mind. How much does that 320 grit tumble change or even damage a worm cast trace? I don’t know for sure, though I have had no reason so far to think it is a problem. But why not take a closer look to find out? So I decided to photograph some fossilised worm cast stones before and after a 320 grit tumble, so I could see any changes.
I chose 40 worm cast stones of varying sizes, colours and types. I then arranged them by size, in groups of four, and took photos of them, front and back, before tumbling them for a week in 320 grit.
I wet the stones for these photos so that the traces would show better. The following are the first eight stones:
After the 320 tumble in late March/early April, these stones looked like this:
I next compared the before and after photos of each stone in order to gain an idea of the effects of the 320 grit tumble. The next Post explains the differences for Stones #1 to #8 (not yet available).
One thought on “How Much Does Tumbling Wear Away Trace Worm Cast Fossils?”