Clays causing glaze problems?

[Diane Puckett]

I just fired a kiln of glaze test cups using three ^6 Highwater clays, Little Loafers, Bella's Blend, and Desert Buff. All were slow bisqued to ^04 using the program which came with my L&L. The kiln is calibrated. I had tried bisquing Desert Buff to ^08 but had lots of large blisters, so I went back to bisquing to ^04. All the pots were wiped down with a damp sponge to remove any dust. I purposely did not stack any pots in the bisque firing, as I wanted to make sure everything had as much exposure to heat and ventilation as possible.

 

In this glaze test,

- The Little Loafers pots came out very well with few glaze issues, just an occasional pinhole.

- The Desert Buff all had problems, pinholes inside and out, small blisters on rims, particularly where I layered glazes, and what I call crud appearing on the inside. This even happened with commercial glazes.

- The Bella's Blend was somewhere between the other two clays in having problems.

 

Of the three clays, I assume Little Loafers is the cleanest so should have less organic material to burn out. I have difficulty throwing large posts with Little Loafers, as it has little tooth and tends to collapse. Desert Buff is great to throw with but has given me too many glaze issues. I was hoping Bella's Blend would be a good compromise.

 

Suggestions?

[Chris Campbell]

I think you might want to think of it as a clay/glaze fit problem rather than a clay problem. Find a clay body that suits you in color and handling then look for a glaze palette to fit it. Once you find your perfect clay I am sure the folks at Highwater will be glad to recommend some glazes that work well with it to get you started.

[neilestrick]

What firing schedule did you use for your glaze firings? What model kiln?

[Diane Puckett]

23T Easy Fire. I was having these problems with the Easy Fire slow glaze so got a program from another potter.

100 degree ramp to 250

250 degree ramp to 2000

75 degree ramp to 2150 with 15 minute hold

500 degree ramp to 1850 with 15 minute hold

125 degree ramp to 1600

[bciskepottery]

Try Highwater's Buncombe White . . . doesn't fire quite as white as Little Loafers, but it has kyanite in it to give it some tooth. Maybe consider blending Little Loafers and Buncombe white 50/50.

[Chris Campbell]

bcisketpottery just posted a link to a blog about glaze fit which directly ties into this discussion.

Glaze and clay must fit each other. Beading, crawling, cracking, crazing etc lies in incompatibility between the two ... it's not the 'fault' of either one ... One size does not fit all.

Many think commercial glazes are designed to fit all clays but that would be impossible ... excellent glaze/clay fit is hard to achieve and seldom occurs without trial and error and scads of reading and of testing ... which is why it is so great to see it and be able to achieve it firing after firing.

If you want to be able to glaze with confidence then you have to bite the bullet and read those scary books and run some glaze tests. Or take a glaze workshop or just a workshop with someone who understands glazes and ask every question you can think of.

** disclaimer ... I personally do not glaze with confidence, but I know why I don't and I know how thoroughly I have avoided the chemistry that I need to know in order to turn that around.

[clay lover]

I used Desert Buff for years, no problems, with many different glazes. Last Spring, using the same glazes , kiln and firing rates, it began to pinhole. I adjusted many things, never got it any better. Finally I slowed the first down firing rate from 500* to 400* and it helped a lot.

 

I don't think their QQ is as tight as some might wish it was. I figure there are different things in the clays, based on availability and price, and I , as the customer, don't get that information to be able to adjust to it.

[neilestrick]

23T Easy Fire. I was having these problems with the Easy Fire slow glaze so got a program from another potter.

100 degree ramp to 250

250 degree ramp to 2000

75 degree ramp to 2150 with 15 minute hold

500 degree ramp to 1850 with 15 minute hold

125 degree ramp to 1600

 

 

For your peak temperature, you may be better off putting in a cone number instead. So rather than 2150, put in cone 5 or 6. That way you'll be sure you are getting the proper heat work. To do that, push the 'Other' button and it will allow you to input a cone rather than a temperature.

[Diane Puckett]

I appreciate everyone's suggestions. I have done lots of reading about glaze chemistry over the last year and a half and taken John Britt's week-long glaze chem class. In the last couple days I have spoken with several people who have expertise in glazing and experience with these clays and glazes. I am not the only one who has been having these same issues with these clays. It seems to more of an issue with clays with grog. My hunch is that it is a problem with one of the minerals and perhaps requires a longer hold during the bisque firing. I don't think fit is the issue, as I have not had crazing or shivering.

 

I have a very small studio and do my glaze mixing outdoors. With winter coming, I plan to put further glaze development on hold until spring. In the meantime, I am going to use Little Loafer, as it does not seem to cause problems with my glazes. Highwater is six miles from my place, so I am hoping to work out ways to use some of their other clays.

[Diane Puckett]

23T Easy Fire. I was having these problems with the Easy Fire slow glaze so got a program from another potter.

100 degree ramp to 250

250 degree ramp to 2000

75 degree ramp to 2150 with 15 minute hold

500 degree ramp to 1850 with 15 minute hold

125 degree ramp to 1600

 

 

For your peak temperature, you may be better off putting in a cone number instead. So rather than 2150, put in cone 5 or 6. That way you'll be sure you are getting the proper heat work. To do that, push the 'Other' button and it will allow you to input a cone rather than a temperature.

 

 

My witness cones were okay for cone 6 on each shelf. Do you still think I need to change this?

[Diane Puckett]

I used Desert Buff for years, no problems, with many different glazes. Last Spring, using the same glazes , kiln and firing rates, it began to pinhole. I adjusted many things, never got it any better. Finally I slowed the first down firing rate from 500* to 400* and it helped a lot.

 

I don't think their QQ is as tight as some might wish it was. I figure there are different things in the clays, based on availability and price, and I , as the customer, don't get that information to be able to adjust to it.

 

 

I agree with that issue. With your slower firing, is that for bisque or glazing firing?

[Diane Puckett]

Try Highwater's Buncombe White . . . doesn't fire quite as white as Little Loafers, but it has kyanite in it to give it some tooth. Maybe consider blending Little Loafers and Buncombe white 50/50.

 

 

Interestingly, when I consulted with one of Highwater's tech people about this, I was advised to not use Buncombe White.

[neilestrick]

[quote name='clay lover' date='06 December 2012 - 07:55 AM' timestamp='1354802148' post='26081'

 

I don't think their QQ is as tight as some might wish it was. I figure there are different things in the clays, based on availability and price, and I , as the customer, don't get that information to be able to adjust to it.

 

 

From a quality control standpoint, it's incredibly difficult, if not impossible, for the clay companies to test for things like this. They can't test every firing and glaze scenario. They also can't alter a formula or substitute an ingredient every time things get a little goofy. It would just anger the bulk of their customers who aren't having problems. It could be something as simple as a change in their water, or the section of the mine that a certain fireclay is coming from. By the time they identify the problem and make changes, the problem will have disappeared. We have to accept that there a too many variables in ceramics to make every clay and glaze fool-proof. It could even be something in our throwing water and not related to the clay supplier at all.

[Diane Puckett]

[quote name='clay lover' date='06 December 2012 - 07:55 AM' timestamp='1354802148' post='26081'

 

I don't think their QQ is as tight as some might wish it was. I figure there are different things in the clays, based on availability and price, and I , as the customer, don't get that information to be able to adjust to it.

 

 

From a quality control standpoint, it's incredibly difficult, if not impossible, for the clay companies to test for things like this. They can't test every firing and glaze scenario. They also can't alter a formula or substitute an ingredient every time things get a little goofy. It would just anger the bulk of their customers who aren't having problems. It could be something as simple as a change in their water, or the section of the mine that a certain fireclay is coming from. By the time they identify the problem and make changes, the problem will have disappeared. We have to accept that there a too many variables in ceramics to make every clay and glaze fool-proof. It could even be something in our throwing water and not related to the clay supplier at all.

 

Absolutely. But it is very difficult for those of us who are new to glaze making and firing, as it adds another inconsistent variable. In retrospect, starting with only one, generally glaze-friendly clay would have been wise. One more thing that seems so obvious now, but was not early in the process when everything was overwhelming.