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Electra

Underglaze with gloss glaze coat firing

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Hi Iam a pottery and ceramics newbie.

I ran a glaze firing with plates, pots and cups with underglaze paints and gloss glaze on top and I put the temperature at 1000 degrees and a rate of 180 degrees every hour. I took the glaze out when it was ready and got a milky cloudy effect on the products as if the gloss glaze wasn’t correctly fired. The colors of the underglaze paints aren’t as bright and vivid as usual because of the milky layer. 

My question is: do i re-fire them? 

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Hi Electra and welcome to the forum.

Sounds like boron clouding and a refire won't get rid of this but a couple questions to clarify, first off what cone is the glaze meant for? It's a lowfire glaze?  Secondly, is it a commercial glaze or one you mixed from a recipe and if so would you post the recipe? 

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Hi Electra,

Are the milky/cloudy portions all over the pieces, just on the inside, outside, over the underglazes, patchy, or? Could you post some pictures? 1000C, that's cone 06 or so? Can you identify the clay and provide the clear gloss recipe as well?

I've had red stoneware (midrange, cone 5/6) pieces cloud up clear glazes - where tiny bubbles are caught in the glaze; one of the clear glazes I've tried clears the bubbles well, so I use that one on the red stoneware.

...have also had milky clouding (not bubbles) in the local Junior Collage's clear glaze. As the clouding was localized/patchy, tried thoroughly mixing the glaze bucket, ladling some out to a smaller bucket, then sieving the glaze*, adjusting the specific gravity and thixotropy**, then glazing my pieces - problem solved, no lumps, consistent thickness.

Any road, the forum regulars may have more/other suggestions - please provide details!

 

*I have five gallon bucket sized 80 and 100 mesh sieves; for test batches and (particularly) sieving small amounts at the JC lab, I bought a roll of 100 mesh stainless screen, some PVC plumbing fittings, and made several smaller sieves for myself and a few others.

**As suggested by Tony Hansen (and others; Tony has a good, err, great, video on the subject and has also written up detailed instructions), a bit more watery whilst more thixotropic is the ticket for dipping.

https://www.youtube.com/watch?v=Ck_69eGJons

 https://digitalfire.com/4sight/glossary/glossary_thixotropy.html

 

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