Polishing problems people have polishing lapidary slabs.
Here is what I have found out: eliminate polishing problems with lapidary slabs. Slabs have a tendency to stick together in the 12 pound barrel tumblers. Follow tumbling instructions for best results. The slabs must be kept apart in the tumbling action to get a good polish.
A good quantity of small sized rocks must be added to each barrel of rocks that are tumbled. These keep the slabs apart. The sizes of rock are from BB size up to bean size. Most people just throw these away if they crack up their own rock. Keep all of the “floor sweepings” -the stuff that is left over after the rocks are crushed. Throw these little pieces into the barrel with other small broken rocks to be tumbled.
For each load use this as a guide.
You can have as much as 1/2 lapidary slabs, 1/4 regular sized rocks and about 1/4 or less being the real small rocks that I call “scrubbers”. These are actually the grinders as they carry the grit in between the slabs to grind off saw marks. They help smooth of any rough spots. Each small rock also grinds in between the crevices and curves of the other rocks. The mix also carries the polishing powder so these areas are also polished. Slabs come out nicely polished this way.
What to do with the tiny chips when polishing slabs?
I have set up and sold at rock shows where I have put them in small plastic bags and sold them to children. You may donate them to rock clubs. Save them for others if you find you have no use for them.
When polishing slabs let Load run 10 days to two weeks.
The next thing I would stress is the time I let my loads run. Loads usually run on average 10 days. For the rough grind, one time through may not be enough time. When you take your rocks out of the rough grind examine them. After washing, spread them out to dry. All the rocks that are not as smooth as you want them to be, put back in for another rough grind. When the rough grid is really good, the rocks then go into the second (220 grit) stage of grinding. This is also for at least 10 days but it never hurts them to go longer.
Next stage is a pre polish. You may use an aluminum oxide for this or 500 grit silicon carbide. Run this again for 10 days.
Polishing stages for slabs
Cerium oxide polish for 10 days is usually good for the polish. Give the rocks an hour in a laundry soap wash (burnishing) to finish it off. The rocks are then dried and ready for sorting and separating. If there are some rocks (and there usually is but only a few) that you don’t really like the finish, Set them aside. Deal with them later. You could either throw them into a kids box or if you think they would be good if re- tumbled, put them in the next batch of rough.
My washing process:
My washing process for the coarse grit of a 12 pound barrel after 10 days is as follows. I work outside on a bench using plastic tubs. I use a plastic strainer in the tub and dump the rocks into the strainer so the mud drains through. All this mud is disposed of except any small rocks that go through the holes in the strainer. Then wash the rocks in two or three of these plastic tubs starting with clean water. The water gets cleaner by the second or third wash.
Now we want to save all the rocks but none of the coarse grit if there is any left. I use something like gold panning classifiers or strainers: ½ inch, 1/4 inch, 1/8 inch, and then screen wire size can be put to good use. ( I made my own with metal mesh material.)
For the next grit stage I want all of the rocks except anything that goes through the 1/8 inch size strainer clean for the next stage. If it goes through the screen wire it may contain some coarse grit. All this rock material is saved for the next coarse grit. Remember: I need all the small rocks I can get to scrub between the slabs.
I use a coarse grit, next a 220 grit, followed by a pre-polish, and then the cerium oxide polish and finally a thirty minute laundry soap burnishing. (Rinse the soap off these rocks and they should still appear wet even when dry.)
MORE ABOUT MY TUMBLING FROM A LETTER WRITTEN TO A FELLOW LAPIDARY
On my web page about tumbling I didn’t say anything about how much grit to use. I assumed most people had the directions that came with their tumblers or had done research for that. Now I don’t really measure the grit I use but in the 12 pound barrels I use about 1/2 to 3/4 cup of coarse grit. When I get through running the coarse grit for the two weeks, I never want to see any or at least hardly any black grit left in the bottom of my wash pan. If I see a lot of grit left over as I clean out the rocks I have put too much grit into the barrel to begin with but since I hadn’t measured I can’t tell myself to cut back a tablespoon or so.
When I do see black grit in the bottom of the wash water, I pour off the water and catch and save the black grit and throw it into the next coarse barrel for tumbling. In each new load add a couple of hands full of the real small BB sized rock to help with the tumbling action.
Special note about pre polish and polish:
Some people will save and reuse the pre-polish. This can also be done for the polish from a load. Keep the milk jugs separate and don’t mix the materials. Just add a little more of the pre-polish or polish to what was saved for the next load. Add maybe a 1/4 to 1/2 the usual amount when using some from a previous load. The jugs will usually settle some so the top is just water which should be poured off and just add your new pre polish or polish to the next load.
Some pre-polish loads will have a lot of “foam” in the barrel while the polish does not have the “foam”. NOTE: These milk jugs will freeze in the winter time and then the stuff will run out on the floor. This happened in my “dirty” shop so it didn’t do anything more than make a mess for me when they thawed out.
One problem but solved.
There have been a few times (2 or 3) that I did not get a good polish on a load of stones and I found out it was my fault. I was tumbling some of the material I received from my brother who had passed away. He had some extra hard stones that would not polish. (The last big one I gave to some kid at the bazaar.) These were all harder than agate, jasper and wood and all through the polishing step instead of polishing it would just scratch so the whole batch of stones just came out all SCRATCHED or cloudy looking.
I knew it had to be something in the batch of rocks so I sorted through each stone to see if I could see something different about it. What I found were a few “real heavy” stones that had to be the culprit. These were left out and the load of rocks put through the 220, pre polish and polish again and they came out perfect.