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Bisque at 4 vs. 04


Lauri Tru

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I accidentally bisqued at 4 (instead of 04 ).  They are all decorative pieces. We usually glaze fire at Cone 5. To glaze now, I have 2 questions...1. Do I need to buy special glazes now to adhere, and to get a good color and luster effect?   If so, What cone glazes?  And 2. ).  What cone  now to fire for glaze?

Thank you!

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We bisque fire to the lower cone so that the wares will be strong enough to handle while glazing and still porous enough that the water in the glaze slurry will be drawn in and the glaze will stick to the surface. When a piece is mistakenly fired to glaze temperature, the surface is now nearly vitrified, no longer porous, and it will be much harder for the glaze slurry to stick to the piece. The second glaze firing will still be the same as usual so the same glazes can be used - if you can find a way to make them stick. If you are using premixed brush-on commercial glazes, they contain an organic brushing agent and binder to make them easy to use. That binder will also help it stick to the nonporous overfired bisque ware. It will take longer for each coat to dry, so be patient. If you are using dipping glazes, then you must resort to special tricks to make it stick. Heating the piece before dipping will help the glaze dry faster. Some use cheap hairspray or laundry starch to create an artificially sticky surface. I've mixed some brushing agent (a CMC gum mixture) into a small amount of the dipping glaze for a rough approximation of a brushing glaze, and I've even heard of mixing white glue (e.g. Elmers is a common brand name) in the glaze to make it stick.

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You can use your normal glazes, but you'll have a hard time getting dipping glazes to adhere. Brushing glazes will work better, but that first coat will still be difficult since they pots are no longer porous. It helps to warm them up a bit. Then go ahead and fire them to your normal glaze fire cone.

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