Yesterday, I placed an order for my polishing abrasives. I get mine from The Rock Shed in Keystone, SD, just a few miles from Mount Rushmore. They have a top-notch reputation and supply rock polishing supplies (including rocks) all over the U.S. My best friend went to high school with the owner. The business was started by his mother back in the day.
I ordered:
5 lbs of 46/70 Silicon Carbide grit
2 lbs of 500 Silicon Carbide grit
3 lbs of 1000 Aluminum Oxide pre-polish grit
I got an email this morning that my order has shipped!
I still have some grit, but this is the stuff I was low on or out of.
The 46/70 is a very coarse abrasive grit used for shaping hard rocks. I use Silicon Carbide because it is harder than quartz, and when it breaks down, the edges remain sharp, so it retains its abrasive ability.
The second step is with 120/220 Silicon Carbide. Same as above, except it is a finer grit. Like sandpaper, when you use a coarse grit, it leaves scratches. Then you use a finer grit to remove those scratches. But that leaves scratches, too, so you go finer and finer until the scratches are so small they are invisible to the naked eye.
The third step is with 500 Silicon Carbide (the higher the number, the finer the grit).
The fourth step is with 1000 Aluminum Oxide. AO does not retain its abrasiveness when it breaks down. The edges become rounded, which makes it a great pre-polish.
The final step is an Aluminum Oxide polish, which I think is about 8000 grit. There are other polishes available, and some people prefer Cerium Oxide over AO, but it is more expensive. I also mix the stones with plastic pellets in the polishing stage. That helps cushion the stones so they aren't bashing against each other, causing chips and cracks. The pellets also help spread the polish evenly all over the stone for a better final finish.
The first step takes the longest. It can take anywhere from a week to several months, depending on the hardness and starting shape of the rocks. Softer rocks, or those that are already rounded, can skip this step. If a rock has a lot of jagged edges, I will lop them off with a Dremel cutting wheel before they go into the barrel.
All of the other steps take about a week to complete. At the end of each week, I empty the barrels and inspect each stone. If it needs more work, it will go back into the barrel for another week. If it is ready to move on, it will go into the next stage's barrel.
Start to finish, it can take five to ten weeks, or more, to finish polishing a stone. Even then, sometimes I need to do some touch-ups with a Dremel, then drop it back into a barrel for another week.
Each week is also a maintenance day. Before starting the next stage, I do a quick check of the machines, clean any dust or debris, and see if they need a drop of oil on the bearings.
It won't be long now and I'll have the machines rolling again.
