Lapidaryforum.net
Let's Rock => Rock Talk => Topic started by: Quitclayton on October 12, 2018, 07:28:56 PM
-
I recently got a piece of petrified wood and sliced off a slab for cabs, but noticed right away that depending on the ''grain'' it had extremely different properties when polished.
Does anyone here have any experience or suggestions for polishing up this stuff before I do more cabs?
-
It varies greatly depending on the quality of the material you are working with. "petrified wood" as a material covers a wide range of stones which may or may not be completely silicified. Variants also include opalized wood and carbonized wood, etc.
A picture of the material that you are trying to polish would be helpful. Dull spots and undercutting are common in some types. If the material you are working with has a wide range of hardness in a small area, it can be very difficult to create an even finish...
-
I've cut a lot of Arizona rainbow PW. The most vexing problem I face with PW is fracturing. It is very hard yet brittle. Sometimes you don't see a fracture until final polish, and that can be frustrating. You also get variations with the grain. As you mentioned, sometimes it polishes, sometimes not. I'm not sure there's a definite answer to your question. Like a lot of stone, the variation in cabbing quality is a wide spectrum. At risk of taking heat from the cabbing purists here, if I'm doing a bunch of cabs, I'll vibe tumble the finish which does a pretty good job. Otherwise, standard sanding and final polish with cerium has worked well for me. Regardless of the challenge, I love to cut PW... the colors and variations are just too interesting to ignore. Good luck!
-
No heat from here for the vibe tumbler polish. The only commercial cutter where we live does that exclusively.
-
I am not a purist per say.... I like to hand cut and polish my cabs. I have over 100 cabochons on the bench and in stages right now. My major market is to consumers who want cabochons that I hand mine and hand finish as well as those pieces I out in jewelry I make. Yep, it is a small and special market that I fit in with and appreciate. My prices on these special pieces reflect the value of Hand Made cabochons...
But, I do use a vibratory tumbler at times. When I am doing cabs for the under $40 price range they may go into the vibe after the 280 grit wheel. I put them in 600 grit polish for 3 days. Then it is back to the Diamond Genie. This middle stage removes a lot of little pesky marks that I see on way to many cabochons that are just done quickly. These are the marks you see when you look at a cabochon with optics and roll it under a strong light. Also those tiny little flat marks you may see on many stones of mid quality.
feel free to visit my website or flickr page for examples... blueowyheegems@aol.com or https://www.flickr.com/photos/blueowyheegems/sets/
PS: I have found that vibratory tumblers are not kind to stones that under cut or have mixed hardness