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Troubles With Glaze Blistering


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I've been using this glaze for many years but have recently been encoutering some pretty bad blistering and some minor pinholing and I"m a bit mystified as to it's cure.

 

The glaze:

 

53 Frit 3110

25 Spodumine

2.8 Strontium Carbonate

3 Silica

13 Gerstley Borate

.6 Whiting

.1 Magnesium Carbonate

2.5 Zinc Oxide

 

5 Rutile

.5 Cobalt Carbonate

1.5 Black Copper oxide.

 

At first I thought maybe it was getting old and since it contains soluable ingredients should be remade but it still blistered. It is a cone 6 glaze so I took it to cone 7. Blistered. Held it for a half hour at cone 6. Blistered. Changed out the Whiting and rejuggled the other ingredients. Still blistered. Thought that maybe something wierd was going on with the Zinc (it hardened) and replaced that with fresh. Still Blistered. On a recommendation from the local ceramics supplier I re-did the elements in the kiln (still blistered though they needed changing anyhow).

 

Out of all the glazes I use, this is the only one giving troubles and it never used to be a problem. Firing it to cone 6 a second time cures the blistering. My next step it to change out the clay body and after that purchase all new glaze ingredients from a supplier on the other side of the country.

 

Does anyone have any advice on this?

 

Thanks much in advance.

 

ps. Everything is bisqued to cone 04 before glazing and no changes have been made to the process except a new batch of clay body was purchased.

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ps. Everything is bisqued to cone 04 before glazing and no changes have been made to the process except a new batch of clay body was purchased.

 

Could be the issue. If the clay has more carbons than normal, could cause the pinholing and even the blistering if enough gasses are in there. Try holding your bisque a bit longer at 1500F for say an hour and see if the next test has same pinholing and blisters.

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MAybe slow down the upper stages of your glaze firing,and soak as before, If it cures on second firing maybe just needs a bit more heatwork.....    

Think there has been talk of gb beigna bit tricky, I haven't experienced this but I did buy stuf many years ago       

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