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Underglaze


Brenda Riggs

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I’m making a container that has 2 pieces, a lid then the bottom. I’ve been told that you need to fire them together because they shrink together. My question is when I do this, will the fuse together because of the under glaze that I used. If I use wax to separate them, will the wax run down my peice? HELP.

thanks

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Underglaze usually does not fuse. However, if the kiln is fired higher, could fuse, as would the clay also if beyond its firing range.

Most underglazes have a broad firing range allowing some leeway. Why would you need to use the underglaze on the form where the lid and pot touch?

 

best,

Pres

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Hi Brenda!

Typically the gallery (where the lid sits) and edge of the lid are left bare. Wax burns away in firing - poof, gone! 

I've fired lids and jars separately, several times, having learned the "hard way" that always a good idea to make extra lids; however, if there is something "sticky" on the edge of your lid, it would have to be propped up.

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Hi Brenda and welcome to the forum. What brand of underglaze and to what cone do you glaze fire? A few of the Spectrum underglazes flux enough to become glossy at cone 04, (that's the brand I use the most) I would assume lids would stick with those ones. If you put alumina hydrate with your wax and the underglaze fluxes to the point of being glossy I would imagine the underglaze would fuse with the alumina hydrate. Just for safety sake I would take a couple test tiles, apply the same underglaze to them as on your container and fire them. If the test tiles stick together then you'll have to fire the container pieces separately, the lid on a clay risers/stilts to get the rim off the shelf. 

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Some underglazes will work without sticking at cone 04, others won't. Most will all will stick if you fire hotter than that, though. You can use alumina hydrate in your wax to keep the two pieces from fusing, but the alumina will fuse to the underglaze, which won't look good. Your best bet is to leave raw any areas where the pot and lid will touch.

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