Tumbling Lapis

Can someone here give me some tips on polish/tumbling lapis. I have a few pieces of lower grade stuff and some of the darker pieces came out horribly. The piece at the very top is fairly "shiny" but most have a satin-type finish to them. Unfortunately, my two favorite darker pieces, have a rough feel to them. I do think part of my problem is that I polished them with harder stones. Can I re-tumble them with...let's say marbles? If I can re-tumble them at what grit stage should I start?

Many thanks,

Henry
San Francisco Bay Area

I would say your major problem is tumbling the Lapis with harder stones after the first grit. When I tumbled I always added harder stones with the first grit( being from Maine we are frugal and it saved spending money on grit). After the first grit I culled out the harder stone. So I think if you returned to the second grit and start out again you should be able to produce some nice but smaller tumbled Lapis. Also consider what you add when polishing - I used various items like plastic pellets to the polish.
Let us know how your project turns out.
Tom

Hi Henry.I thiink that adding some marbles or any glass items as a filler might be a good idea,as it hardness of 5.5 equals the lapis' hardness.Always keep in mind that you need to have materials of the same hardness when you start a batch.I also suggest trying a prepolish,such as 600 grit aluminum oxyde(after having used 500 or 600 grit silicon carbide grit),as aluminum oxyde tends to break up to rounded grains,helping for the removal of scratches left by the 600 grit silicon carbide,making it easier to reach a higher polish.You may also consider trying different polishes.I think cerium oxyde is the best polish for lapis,but i'm not sure.

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Edited 2 time(s). Last edit at 04/14/2010 05:22PM by Wizard Stone.