Electric Mid&Hi Fired Ceramics
Cone 6 Glaze Testing & Reporting
Collaborate on building an online list of well documented glaze recipes, with application and firing methods. Strong photo documentation. Only glazes that are mature at cone 6 will be included.
Testing the glazes, and identifying their problems and fixing them. Also, if there are obvious issues just by looking at a glaze recipe (like high barium, insufficient clay to suspend or harden, too much feldspar (which causes crazing), too much clay (causing crawling, peeling), hard-to-get materials, non-specific materials, etc) then it needs to be fixed as part of the testing I would say.
Tony Hansen included links below to procedures for a few glaze tests that could be done. Another good one would be to appraise the rate at which it settles, how hard is the dry layer, the water content of the slurry, the viscosity, these could be measured with commonly available tools.
Links:
What causes glazes to react with each other
I have noticed that glazes often tend to either react when layered or are quite stable and do not mix. If anyone has any insights into the chemical reactions I would like hear. It seems like there are times you would like to encourage two glazes to interact with each other.
I have heard of some artists who multifire at successively lower temperatures to allow them to layer glazes much like a painter may add colors and details successively. I have found that refiring a piece with a second glaze over the original results in little to no mixing of the glazes - usefull to change a design but why is it that the glazes don't mix?
What if you wanted to encourage this? Would the secret be in adding flux, adding something between the two glazes? Would it be possible to change a fired glaze after the fact by adding a layer on top and refiring (for instance I have been able to reduce crazing by refiring with a pure silica wash, crazing is reduced although the surface becomes rough and matted).
About all I know about this is zinc in a glaze can change colors in some stains and some high iron glazes can produce some nice effects as the run down the side of a pot into other color glazes.
Brent Farler
rather than the flow/run what about the mixing of two glazes. Would this imply if both are high in calcium, magnesium or strontium they won't mix and if high in sodium, potassium or lithium they would 'mix' i.e. tend towards more mixing of the colorants.
Another way to look at it is what makes one pair of glazes 'coat' one another versus what makes another pair of glazes mix and react with each other?
May 18, 2017
George Lewter
Glazes layered or in contact with each other can exhibit wild behavior due to eutectic melting. Material components that have higher melting points by themselves can have drastically reduced melting points when mixed together, or in contact with each other. Quite often two very stable glazes, individually, will run off a pot when layered together.
May 18, 2017
Brent Farler
sounds like, experiment and test, experiment and test, experiment and test, repeat.
I am guessing the amount of soak at the target cone can have an effect as well. so fluidity + time at temperature
George Lewter said:
May 18, 2017