Are there any additives to make a commercial glaze craze at cone 6?

[Kathryn Howlett]

I fire at cone 6 at a community kiln and use their dipping glazes and Amaco commercial glazes.. Is there any additive which would make these glazes craze? I am looking to increase crazing. 

 

[Hulk]

Hi Kathryn,

Welcome to the Forum!

Good questions.
Given a good glaze fit (no crazing), some adjustments could be made to induce crazing, which would likely start with a few cracks where the glaze is thickest and where there is more stress - a wide pattern*.

However, making adjustments is more straightforward when the glaze recipe/formula is available, so, broadly speaking, adjustment can be made while other glaze qualities remain fairly constant - when it melts, how glossy, how much it sags/runs, color, et cetera...

I'm curious to see further discussion on the topics!
 

*In the other direction, eliminating crazing, if the craze pattern is large (just a few cracks), adjustment to a good fit might be possible, however, if the craze pattern is fine/small, the required adjustment may be out of reach...

[Min]

Do you have the recipe(s) for the dipping glazes?

Are you permitted to underfire the kiln or are there other peoples work in the same kiln firing? Are you making functional work?

[Kathryn Howlett]

this would be for decorative work like the outside of a vase.  I have no control over the firing schedule but have been told it is a standard cone 6. I have commercial paint on glazes and the studio has dipping glazes. I will see if I can get the recipe for the clear and the gloss white studio glazes.  

 

[Min]

You can run into problems of dunting (a type of cracking of the pot) when using glazes that have fairly different coefficients of expansion (COE). The crazed glaze is going to have a higher COE than a non crazed liner glaze. You could use the same crazed glaze both inside and outside the vase but make sure the clay you use has a low enough absorption to not leak. Absorption should be below 1 - 1.5% for functional work, including vases. Link here for how to test for absorption if you need it. https://ceramicartsnetwork.org/daily/article/Testing-1-2-3-How-to-Test-Clay-Bodies-to-Find-the-Right-Sculpture-or-Pottery-Clay-for-Your-Work#:~:text=The weight calculation test is,weight of the absorbed water.

[High Bridge Pottery]

Sodium has the highest expansion so adding soda feldspar or a high sodium frit are your easiest options to start with. 

[Min]

@Kathryn Howlett, whatever testing you do I would strongly suggest putting a waster cookie or shallow dish under your glaze tests in case you get glaze running onto the shelves. The waster cookie or dish can be reused.