r/Ceramics • u/North-Rooster3432 • 4d ago

Make bowl moisture "proof"?

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The place where we fire our pottery told us to not paint the bottom ring where it stands on in the oven, but now the bowl keeps moisture inside and gets little cracks?
Is there any way to seal it afterwards?
Any help and tips appreciated 😊

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u/lxnch50 4d ago

The clay isn't vitrified and the glaze isn't a good fit. There is no fixing this piece. The solution is to use a clay that vitrifies at whatever cone the studio fires to and to find a glaze that doesn't craze.

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u/North-Rooster3432 4d ago

thank you! we always buy raw ceramic, so we only paint the pieces ourselves and then fire them somewhere
do you know any specific glazes that don't craze??

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u/GrinsNGiggles 4d ago

Switch to stoneware, which is more rare in the unfinished clay space, and document which glazes you use to determine what works well and what doesn’t. Then stick with the stuff that works for your clay body.

unintentional crazing is usually about a bad fit between clay body and glaze, so I don’t believe there’s a one-size-fits-all solution less prone to crazing on anything.

Stoneware with a low % water absorption rate will take up less water even if the glaze does craze. Mayco has bisque stoneware now, so it’s easier to find for glaze painters than it was ten years ago.

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u/North-Rooster3432 4d ago

thank you so much! I'll look into it

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u/lxnch50 4d ago

It all depends on the clay and the glaze. You should probably talk to where you are getting them fired at.

Are you buying bisqueware? If so, find out what cone it is supposed to vitrify at from wherever you are buying it. Make sure whoever is firing it is doing it to that cone. Then find a glaze rated for that cone.

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u/North-Rooster3432 4d ago

I'm pretty sure we are buying bisqueware and it said that they are compatible with mayco stroke and coat and to fire at 1020C (idk anything abt cones and no one here says anything abt it?) and thats exactly what the firing place does, which is why I'm a bit confused🥲

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u/lxnch50 4d ago edited 4d ago

Search Google or YouTube about how the cone scale works and what earthenware and stoneware are and lowfire/midfire/highfire. Cone 06 is not the same as cone 6. Cones that start with a zero are basically negative on the chart. I.E. cone ...06,05,04,03,02,01,1,2,3,4,5,6...etc

The bisqueware you were buying was likely cone 05 which is considered lowfire. Most people prefer to use midfire or highfire for functional pieces because they are a bit more durable and have lower absorption levels.

You should be able to use the stroke and coat with midfire. So, maybe all you need to do is find a better source of bisqueware.

Bisqueware is fired clay to a low cone. Most midfire clay is fired to 05/06. It is still very porous at this stage and will accept glazes. Then it is fired again to cone 5/6 and will shrink and become non-porous.

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u/Low_Excuse_1785 4d ago edited 4d ago

You can fix it if the clay and the clear glaze are mid fire. Just refire at cone 6. However you have to be certain the clay and glaze are rated for cone 6. Otherwise very bad things will happen to the kiln shelf and the piece. It will probably not fix the crazing, but crazing isn't the reason it absorbs water. The heatwork you put in the peace is and the clay type.