Polishing, Finishing, and Abrasives (Porcelain)

[colekeller]

I was wondering if anyone could speak to using tumblers(either vibratory or rotary) on their porcelain objects to attempt to finish/smooth/polish them? I love the look of unglazed porcelain and therefor have been searching for a way to consistently and easily finish the surface for a smooth feel. I have tried sanding, and although extremely successful, it is much too labor intensive. Additionally, sanding doesn't allow for polishing hard-to-reach areas. 

Basically I am just curious if anyone has any experience using tumblers to finish porcelain or other fired clay bodies and what type of tumbling media they might use. Would porcelain be good media for polishing porcelain? Not sure if that would work. I am currently attempting tumbling porcelain with crushed walnut shells but to no avail. I think the media is too soft. Anyways, any thoughts would be greatly appreciated!

Cole

[hitchmss]

So I have never tumbled any porcelain objects, but would think that steel shot, or more porcelain would be the best objects to polish the surface. You might try looking for a compound designed for masonry polishing and add that to the tumbler.

Im assuming these objects are relatively small (thinking like bead sizes) which is why it is a pain to sand/polish them to the surface you want. If that is the case, you might try overfiring your objects; the more the body fluxes out, it will give you more of a glossy surface. It will still feel "rough" and wont be mirror like surface, but it will be glossier and smoother.  I of course wouldnt try this with table ware as the added stress on your objects will not be good.

You might also consider a terra sigillata using a porcelain clay recipe. The ball milling of a true sigillata will provide you with a very fine/tight grained clay, that in my opinion, offers the best silky matte surfaces you can put on a pot. I love the look of a leather hard pot, which is similar to that of unglazed porcelain, and IMO a sig will do that for you. You can dip or spray for the most even surface. It will not however hide blemishes well, and in some cases accentuates them, but if your pots are clean to begin with, and you can get a nice even coat of sig on them, it might give you that surface you are looking for.

You can also try other porcelain recipes; not all porcelains are alike. A more translucent porcelain is designed to flux out more, and therefore will provide you a glossier surface; one with more grolleg vs helmar vs epk...... The mesh size of your clays, and the ratios of which items you are adding will have a big impact to their finished surface. You could (if the items you make are small, and dont use much material) ball mill all of your dry ingredients so you can get a super fine mesh size to them, and add them to your clay recipe from there. You may experience a lot of shrinkage/cracking issues with a super fine grained clay body, but only tests will tell.

[neilestrick]

If you have small objects that don't have small parts that stick out (breakable), it could be possible to tumble them. I would use silicon carbide and water, like you use for tumble polishing rocks.

[Fred Sweet]

Cole-

What Neil says. I had a few former students who used it to polish their colored porcelain jewelry pendants in rotary rock tumblers. Of the students, one used two or three different grit sizes (and perhaps also more time) which were the more successful in terms of polish and “softness” of the finished products. I seem to remember that she finished with 400 grit, though it was a long time ago and my memory isn’t up to remembering the exact grits used and time per grit.

Regards,

Fred