Hello fellow potters! I was wondering if anyone has any experience burnishing pottery? I am trying my hand at creating slab bonsai pots and would like to try burnishing. I have grown up around southwestern pottery being from AZ. Indigenous potters used burnishing to create a gloss and color on their pottery. My goal is to create bonsai pots with a southwestern flair. I was wondering if anyone has burnishing experience and would be willing to share some tips? Thanks.
Burnishing Pottery
- Thread starter AZbonsai
- Start date
sorce
Nonsense Rascal
I grabbed my good smooth doorknob to "hammer" a chisel across my shelves to clean some glaze, that was dumb, it was good for burnishing. I put a rock up from the yard the other day as a possible replacement.
Sorce
Freezing?
yes. That said, I polished a pot painted and burnished with engobe. Fired it to 05. It retained some shine but I didn't get the full effect.
penumbra
Imperial Masterpiece
Yeah, burnishing is generally for pit fired and raku pottery which are low fire. You can also use burnishing for high fire on a clay body that might otherwise be gritty, to give it a smoother finish. Burnishing is also good to give you a tighter clay as it compacts the clay, particularly good to help with the prevention of s cracks that develop on the bottom during firing. If you like the effect that you generally see in low fired pieces, like those in your picture, you may be able to produce those effects in a sagger with fuming.
Good luck.
Good luck.
sorce
Nonsense Rascal
Since my analogy to describe the truth is with a dream catcher, I have to call BS on this in this thread!
Seriously though. "Compressing" the bottom is one of the most widely spread "prevention's" of s-cracks, but it isn't preventative, as proof particularly in the fact that these s-cracks are showing up "after the firing".
That means the stress was there to begin with, and it is seperated with the added firing stress. In this case, where drag on feet from shrink may be enough to tear the piece, it is certain that a well compressed bottom is strong enough to make it through firing. Then we have a situation where the fired pot is the same strength as the ones that crack, before the firing. Only now, as with a mug say, it's next test on that stress point is in the customers hands, with a hot liquid poured in.
I've had hot coffee poured in my lap. Sucks. Bad. I think that's why I hold this concern. But this is the point where liability comes in. The point where it is imperative that we actually prevented the problem in the first place.
S is for Shrink.
Enter the Dream Catcher.
The reason s-cracks form is ONLY because the edge dries faster than the middle.
Imagine the brown rim as the pot edge, fully dry, and shrunk to it's smallest solid state.
Now the still wet slab of the center needs to shrink too, it can not pull itself from the solid ring, so the s-crack forms to relieve that stress.
The best advice to prevent it while throwing is removing water from the inside. Though I'd Further it and add, use as little water as possible on the inside, and continually run a wet finger around the bottom outside edge, to keep it wetter than the inside middle. Centrifugal force will also help push center water to the edge, so just leaving the pot spinning for a while will help.
Bonus trivia question....
Why are s-cracks backwards in Japan when they are still in the Northern Hemisphere?
I had a long hard study of s-cracks when this broke after 6 hours of carving work.
Almost time to try it again!
Sorce
There wheels spin counter clockwise?
penumbra
Imperial Masterpiece
I have not had a stress crack since I paid extra attention to compressing the bottom of my pots. I had several before. No other changes. There is no question that if the bottom dries unevenly you will have stress cracks whether it is well compressed or not. And the point about using too much water is pertinent though not absolute. In my experience paying extra attention to compressing the clay helps to mitigate the uneven moisture. I didn't pull this out of a hat but learned it from master potters. I have actually seen pottery thrown, compressed and put into a kiln still green. I don't believe I could do it myself, but I have seen it done. A very well compressed piece of pottery can be passed from hand to hand and it feels like bisque-ware.
I am talking about wheel thrown pottery here. I have never had an s crack on a hand built piece of pottery.
But all of this, no matter how interesting, does not address the OPs question.
I am talking about wheel thrown pottery here. I have never had an s crack on a hand built piece of pottery.
But all of this, no matter how interesting, does not address the OPs question.
sorce
Nonsense Rascal
Dog bowl oops. I honestly don't remember whether I compressed this bottom or not. But the only reason it cracked is cuz I left it upside down. I was trying to sag the bottom up a little and forgot to flip it back.
This one was left right side up.
I guess my point is, it's not the compression itself that negates the s-crack, it's the other things happening while compressing that actually negates the crack. Like the spinning, or the "squeezing the water out".
I reckon it's physics, likely a law, that says the act of compression, which is just "aligning particles", can not be made stronger than the force of the shrink pull. In consulting my textbooks, it is true that good compression will result in less sideways shrinkage, but I think that is what we can't increase beyond what the force of the shrink can pull.
Just a full cycle thing I can't get over. See too many folks out of balance. Trying to fix Problems with the wrong solution. Like, each clay has specific values for throwing and drying. If they add up to a hundred the piece survives. Some clays need throwing 25 and drying 75. Some are 50 50. Etc. All different. But folks will take a 25 75 and throw it to a 50, dry it to a fifty, and it cracks. So they try to add Points to throwing rather than drying. I think we waste a lot of time doing this thinking all clays are the same. If we focus too much on the wrong problem, we can't grow.
I believe this matters because burnishing is a form of compression, or aligning of particles.
Further, of one is to introduce oil as with se burnishing techniques, you can pretty easily set yourself up a scenario where the phenomenon of the "s-crack" can happen somewhere else on a pot.
I am the proud owner of a RTM pot, that's @AZbonsai, and I couldn't be happier!
Sorce
This one was left right side up.
I guess my point is, it's not the compression itself that negates the s-crack, it's the other things happening while compressing that actually negates the crack. Like the spinning, or the "squeezing the water out".
I reckon it's physics, likely a law, that says the act of compression, which is just "aligning particles", can not be made stronger than the force of the shrink pull. In consulting my textbooks, it is true that good compression will result in less sideways shrinkage, but I think that is what we can't increase beyond what the force of the shrink can pull.
Just a full cycle thing I can't get over. See too many folks out of balance. Trying to fix Problems with the wrong solution. Like, each clay has specific values for throwing and drying. If they add up to a hundred the piece survives. Some clays need throwing 25 and drying 75. Some are 50 50. Etc. All different. But folks will take a 25 75 and throw it to a 50, dry it to a fifty, and it cracks. So they try to add Points to throwing rather than drying. I think we waste a lot of time doing this thinking all clays are the same. If we focus too much on the wrong problem, we can't grow.
I believe this matters because burnishing is a form of compression, or aligning of particles.
Further, of one is to introduce oil as with se burnishing techniques, you can pretty easily set yourself up a scenario where the phenomenon of the "s-crack" can happen somewhere else on a pot.
I am the proud owner of a RTM pot, that's @AZbonsai, and I couldn't be happier!
Sorce
Thanks for your guidance @sorce I appreciate it! Will send you a glazed colander when I get the kiln up and running!
sorce
Nonsense Rascal
sorce
Nonsense Rascal
Meh....it's reciprocal. In speaking with you, I decided to do to this top rim as we were talking about for that bottom lip on my RTM joint.
I picked this up from my guy at the Ceramic Supply, who is always talking about how important it is to consider these facets, and how they interact with the entire piece.
Sorce
HorseloverFat
Squarepants with Conkers
HorseloverFat
Squarepants with Conkers
..and our Son’s collaborative musical effort would be called, “Almost Tree and the Blind Kid.”
