I have found alumina suspension works well for final polishing when a clean, scratch-free surface is needed, especially after diamond stages on metals and ceramics. Particle size and pad selection make a noticeable difference in consistency and finish quality.
I’m a gem cutter so I have no knowledge of polishing metals. But I do use an alumina suspension for quartz at times and a lot of varieties of garnet and also tourmaline. I also use cerium oxide suspension. I use diamond at a 100k for harder stones. My understanding of the oxide polishing is it doesn’t polish by the fine and ultra fine way diamond does by extremely small scratches. It polish’s by some sort of chemical change in the surface. I may be wrong but I remember reading about it several years ago. Royjohn and Troy will be able to clarify what I’m poorly attempting to say.
Bob is correct. Some alumina slurries have a chemical-mechanical interaction with metal or ceramic surfaces, based on the doping formula. The interaction with most gemstone materials (softer than Corundum) is from mechanical abrasion. Depends on the physical properties (i.e. size and shape) and what suspension the alumina is transported with.
Have used paste and slurry alumina as a final polish on flat and cabochon shaped stones, with great success. However, I haven’t begun the journey into gemstone faceting (still only doing cabochons/slabs/intarsia type lapidary). Will have to defer to the experience of others like Royjohn (@royjohn), Bob, and all of the other gem cutters here on the forum.
Leonid (@LeonidF39263): You might find a larger focused audience with interest in cutting/polishing/lapping techniques and supplies on IGS’s sister forum Ganoksin Orchid. That forum is focused on the fabrication techniques for bench jewelers and metalsmiths. Here, the subject is more on gemstone identification and appraisal methods.
Don’t get me wrong, there are plenty of jewelers on this forum, too! Have been enjoying your thought-provoking questions and articles. Keep sending them out!
Well, we started out with polish of metal and ceramic by Alox. Then went on to polishes for cabbing. Theory of polishing was mentioned.
As far as I know, polishing of silver and gold are usually accomplished with finer and finer sanding followed by tripoli and then rouge. Not AlOx, although it might work. There are other polishing media which are sold by jewelry suppliers (see book referenced below).. Best polishing media for minerals when you cab depends on the species. Cerium is best for glass, quartz and beryl. Many other materials which are harder than quartz…garnet, tourmaline and others, are best polished with AlOx. Substances harder than 8 are usually polished with diamond grits, although some of hardness are polished with AlOx alternatively. I think at present flow theories of polish have largely been discredited. Polish is just finer and finer scratches. Oxides break down into finer and finer particles are polishing proceeds and the same thing is true of polycrystalline diamond (PCD). Media for polishing gems, both cab and facet, is pretty settled and AI or any good book on cutting will tell you what to use for various stones. Some people like diamond for everything and especially for troublesome materials of composite minerals which tend to undercut or for species that tend to “orange peel”. However, esp. for quartz, cerium seems best and some people feel that there is some haze when diamond is used for final polish on it. Slurries usually work OK for cabbing, but they have been superceded in faceting by polishes which are coated on a lap or those which are put into a wax binder, like Gearloose’s Battstiks. Slurries tend to scratch flat facets when the medium becomes too dry, but coatings lubricated with water or oil, or polish powders in a wax binder don’t. I hope this helps clarify some things. As far as jewelry metals go, there’s a very good new book on polishing and finishing by Stephen Goldsmith (yes, that’s his name!). -royjohn
I agree with what’s been said here. In my experience, alumina works best when you’re trying to remove the last traces of fine diamond damage, especially on ceramics and oxide-based materials. The results depend heavily on particle size, shape, and how the suspension is delivered to the surface.
On harder, less reactive materials, diamond is still more efficient, but alumina can noticeably improve surface cleanliness and final finish when used at the right stage.
I also know some competition cutters that will polish with diamond then give the facets a kiss on oxides for a final finish. I’ve tried it and it does add a little something.
