Clear Glaze Problem

[Thrown_In_Stone]

Hi Everyone,

 

I have mixed a clear base glaze up and I'm having a few problems with it and wondered if anyone could help?

 

I got the recipe from a book which stated it was for earthenware at a temp of 1050-1100ºC. I fired some tests at 1050ºC and it looks to be too hot. I don't know if the kiln is over firing or if the temperature is too high for the glaze. I don't really have any issues with other glazes.

 

When I fired it at 1050ºC with a soak of 15mins it had run a lot. Also there are tiny bubbles all over in the glaze, does this mean it has been fired too hot and is boiling?

 

I tried another test at 1025ºC with a soak of 15mins the glaze still run a bit but not half as much as the previous firing. These test still had the tiny bubbles in it. Other than these issues the glaze looks quite nice.

 

Does anyone have any suggestions?

 

30 Ferro 3134 (standard borax frit)

30 Colmanite (calcium borate frit)

20 Spruce Pine 4 (Soda Feldspar)

10 China Clay

10 Flint

____

100

 

Many Thanks,

Gary

[neilestrick]

First, why are you adding a soak to the end? A 15 minute soak is roughy equivalent to adding one ful cone to the firing (heat work). So first try it without the soak if it's running. Some glazes will have little bubbles in them. Not necessarily a bad thing, unless they are breaking open. If you need to stiffen up the glaze, add more China Clay and Flint in equal parts, testing at 3% increments.

[INYA]

the bubbles- it could be that the glaze has to be applied thiner (my trensparent glazes have this problem)

[TJR]

FIRST OF ALL, SO DON'T SAY HOW LONG YOU FIRING SCHEDULE IS. THE SLOWER YOU FIRE THE LESS TRAPPED GAS YOU HAVE.

I AGREE THAT YOU DON'T NEED THE 15 MINUTE SOAK.

THERE ARE TWO POSSIBLE PROBLEMS/SOLUTIONS HERE.

1.IF YOU SLOW YOUR GLAZE FIRING DOWN-IN OTHER WORDS EXTEND THE LENGTH OF A FIRING BY AN HOUR OR SO,YOU COULD ELIMINATE THE BUBBLES.

2. YOUR PROBLEM MATERIAL IS COLEMANITE. YOU COULD MAKE A DIRECT SWITCH TO Gerstly Borate, which does not have the same off gassing problem. Of course you must test on test tiles before you glaze your masterpieces.

Sorry, had the caps lock on again from my last post.

TJR.

[Frederik-W]

You say that this is a clear glaze - I'm just curious why, if there is nothing special about the glaze, you don't use a commercial glaze.

It would be easier to use a commercial clear glaze - they are far less of a risk.

Unless of course, your own clear glaze is cheaper, rather special or you like to experiment.

[Thrown_In_Stone]

Thanks for your suggestions everyone. I will give them a go over the weekend.

 

 

You say that this is a clear glaze - I'm just curious why, if there is nothing special about the glaze, you don't use a commercial glaze.

It would be easier to use a commercial clear glaze - they are far less of a risk.

Unless of course, your own clear glaze is cheaper, rather special or you like to experiment.

 

I can make this glaze cheaper than the commercial clear I use. I also love to experiment. I think it's a nicer feeling to know you have made something rather than just buying it, that's too easy.

[Scout]

Interesting! Scout