I have recently acquired a coupe of very nice pieces of malachite in the 13-14 pound range that have beautiful pattern and several concavities producing nice eyes. What is the best method for polishing this material so that the contours of the natural rock are preserved? I though perhaps knocking off all the jagged edges with a the grinding wheel for the larger areas and a dremel tool for the harder to reach places and then going to felt bobs and silicon grit might work but that doesn't seem very efficient. Any thoughts would be appreciated.
UNDER NO CIRCUMSTANCES DO ANY DRY GRINDING/SANDING. Malachite will produce arsenic fumes. Keep it wet. I would not grind dry, even if I has a full face respirator. Rig up some device that will let you grind and sand under water, or at least with water running over it. Also, dry sanding with silicon carbide can produce silicosis. ALWAYS GRIND AND SAND WET.
Harry is correct on not working Malachite dry but the reason is not arsenic but Copper. Malachite is a copper carboate and the dust you breathe in will dissolve in your stomach acid leaving copper to be abosrbed by your system leading to copper poisoning or copper fume fever as it is known. It is no fun and can kill you and if it doesn;t kill will make you wish it had.
There are a lot of dismond points available that can be used to contour grind and polish the malachite. Its a soft stone so the work should go fairly fast but always work it wet. I have used Nova points from Diamond Pacific in the past on fire agates and other carvings with good success.
The Amethyst Rose
Thanks guys! I have all ready set up to work the stone wet and have ordered some diamond points as well. Impatiently awaiting the postman now.....sigh. :-)
You speak of preserving the natural contours of the piece, have you givin any thought about just using wet sandpaper and rubbing the natural contours smooth? That is, after knocking off the edges. It will be more work, but I think the finished piece will mean tremendously more to you. The Dremel might leave ridges used for sanding but mite work great for the polish. Whatever way u do polish, expect a HUGE green stainy mess . . .! I have not personally worked any Malachite as of yet, but do have a wonderfull 30 lber waiting for some inspiration ! Cant remember the name of the polishing compound, but I do know it is green ! ( if I remember right? ) Good luck with whatever method u do use !
I gotta say, I haven't looked up the mohs hardness for malachite but hand sanding this to completion even after working the ridges and lumps down with a dremel sounds pretty excruciating. I switched to some cheapo 1/4" shaft diamond burrs in a regular drill and I'm pretty impressed with it's durability. I'm even starting to find myself thinking.....*why shouldn't I have a 55 gallon tumbler?*..... :-D I'll post a couple of pictures as I progress.
I see this is a pretty old thread, but hopefully someone will see my question about malachite: how do I got about sanding a piece that is already set in jewelry? I have a gorgeous vintage ring with a malachite setting that is quite dark and dull. I would love to avoid paying someone to polish it to brightness if it is something I can safely do myself. Any thoughts? PS: I don't own any kind of sanding tools or devices.
As you may have gathered from the above posts, polishing malachite is not easy and can be hazardous to your health if not done the right way. And if this wasn't a big enough hurdle for your situation, it is generally difficult to impossible to sand and polish any rock or gem that is already set in jewelry. Your best bet, if you really love the piece, is to take it to a professional jeweler or lapidary artisan to have the work done if it is indeed possible to remove the stone without damaging the setting, but I imagine this would end up costing you more than the ring is worth monetarily. Mike
Thanks for the info, I will keep it in mind!
Actually a very easy fix. Have the stone buffed with zam with the stone in place. Should only take a few minutes and will polish the ring at the same time. If you can't find someone to do it email me I'd be happy to do it.
for those grinding, sanding polishing malachite or others use method I use with freeform opal etc:
wet & dry sandpaper up to 3000 grit ( silicone carbide or Trizact ( 3m ) CUT IN STRIPS ( MARK BACK ALL OVER SO YOU KNOW GRIT ) sand by hand using dowel, marker etc for shaping then nylon cloth using polish of choice ( I have a chart from sources including Sinkankas, Chert Chatter) for pockets etc, tiny crystals use mini dremel with 1/2 que tip always WET !! DIPPED IN POLISH FINAL POLISH 50k, 100k, 200k, 300K DIAMOND with extender or cheap olive oil warning : until washed in DAWN VERY SLIPPERY AND YOU DON'T WANT "EARINGS similarily don't pick up from freezer by dop stick always by stone ( don't use this method for opals either ) chart emailed by request