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Achilles

Kiln Wash Ruining My Work

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Achilles    0

In my glaze firings, I have found kiln wash stuck to the inside of some bowls. I checked my shelves and there is absolutely no kiln wash on the bottom  or sides of them, so know it isn't flaking off the bottom of the shelf above and landing in the bowl. My working assumption is that the kiln wash is flaking off of the shelves and floating around the kiln. Does that sound possible? If so, is there anything I can do to prevent this from happening?

 

In case it is helpful to know, I am using pre-made kiln wash that I buy in powder form from the local supplier. I mixed it with water and then brushed it on my shelves. Per the instructions, I applied 3–4 layers in the following manner: apply a coat of wash, let it dry for several hours, repeat. I waited about a week before firing the washed shelves, and I first bisque fired them to ^04, then later glaze fired them to ^6. Nevertheless, the wash seems is brittle and is flaking off.  What should I do?

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Min    784

Problem with store bought kiln wash is you don't know what's in it. If it's formulated and applied properly kiln wash does not flake. I would grind off all the wash you have on the shelves now, wear a respirator and work outside, and mix up some of your own. What I have used for years is 50 alumina hydrate, 25 calcined epk and 25 epk, mix it up with enough water to make it like a thin glaze consistency. I use one of those inexpensive mini paint rollers from a dollar store to put in on with. 2 or 3 coats, depending on how thick you mix it up. Shelves and wash should be dry before you fire them. 

 

Is it kiln wash inside the bowls for sure? Any chance it could be crumbly bits of kiln brick that have dropped in? I'm thinking that the wash would have to be super flakey plus a strong draft in your kiln to have bits of it fly around.

Edited by Min

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neilestrick    1,381

Everything Min said is true. Commercial kiln wash is crappy stuff.

 

If it's actually kiln wash getting into the bowls, it would be white flakes, like rectangular bits. But like Min said it's unusual for that to happen since there's no enough draft in an electric kiln to cause it to fly around. It's possible, however, that it's falling in when you load the shelves in. Watch that. If you're getting little bits of stuff in the glaze that are just little chunks of something, that's probably not kiln wash but rather bits of brick shedding (again unlikely except for the top shelf), or you've got some gunk in your glaze which should be screened out.

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bciskepottery    925

Ditto to Neil's comments on being careful during loading . . . I've encountered that too often at community studios where the loader was not careful. Also, make sure there is no kiln wash on the edges of your shelves that can easily chip and fall onto pottery.

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Babs    386

Is your kiln a toploader/

If so you may be dropping some wash in when placing the next shelf onto kiln.

Better to grind your shelves and re kiln wash them.

From experience, aging shelves can drop deposits but the bits are crumbly bits as opposed to flakes.

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Bummer. I've had this happen and it sucks!
I use the same kilnwash recipe as Min. It's good stuff.
If your shelf is dirty, bits can fall onto the pots below as you load the kiln. I run a dry cloth over my kiln shelf before loading to prevent any loose bits falling in.
Also, my kiln is old so the bricks do sometimes crumble off if I bump or jostle things. I've had more than once piece ruined because of mini kiln-brick chunks falling into the glaze. Loading slowly and carefully does seem to help :)

 

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oldlady    1,323

when my kiln top band started dropping tiny black pepper bits into my glazes, i brushed the metal with a wire brush and used a sheet of paper over the load as i lowered the lid into position.  i still brush periodically.  and the paper is now an "always do this" routine.

 

it is true that the glaze itself may have some bits of stuff in it.  since the use of stick blenders has become common, i found that some people do not sieve anymore.  that could be a problem.  

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Achilles    0

Thank you all for the helpful suggestions.

 

The recipe for kiln wash above calls for "calcined EPK", which I am not familiar with. From what I found online, this is made by firing regular EPK in a bowl. Is it sufficient to fire the EPK in my next bisque firing (come 04), or do I need to fire it to the same temperature as my glaze firings (cone 6) before mixing it with the aluminum hydrate and regular EPK?

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bciskepottery    925

Regular bisque temp for calcining should be fine.

 

The purpose of calcining is to remove chemical water; by doing that, it will shrink less upon drying.

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RonSa    189

Regular bisque temp for calcining should be fine.

 

The purpose of calcining is to remove chemical water; by doing that, it will shrink less upon drying.

 

So how do you keep the EPK from becoming a big lump or is this not a concern?

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oldlady    1,323

it will look the same when it comes out as it did when it went in.  you are only heating it, not adding something that would make it clump.

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Min    784

Adding a little bit to what O.Lady said,

 

 

Epk is roughly 46% silica, 37% alumina and a combined 1 point 2% of fluxes. With such a minuscule amount of flux the alumina and silica won’t melt together. It does loose some colour in the bisque, that is the organic impurities burning off. It has approx 13% of it’s initial weight burn off, some will be chemically bound water, the rest organic impurities. (That is why you can’t substitute epk for calcined epk in a direct 1:1 ratio in glaze recipes, you have to take the LOI (loss on Ignition) into account with the math.) 

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Min    784

Yup that works perfect. Also, if you don't want to wait until you have a bisque load to do you can just take it up to around ^018 (dull red kiln colour if you don't have a controller or cones) and hold it there for about an hour by lowering the dials a bit. Use a shallow bowl so the heat can penetrate into the middle of the epk. If it comes out lighter in colour than it went in you are good to go.

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Mark C.    1,807

You can put it in any form from mugs to bowls to plates -its just a pile of powder going in and coming out.

You can wash out the form with water or blow it out with compressed air to clean it for glazing.

I keep a bag of this ready for making wash at all times.You can also by it from clay suppliers its called Glowmax.

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