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:
Viscosity and surface tension
I came across a set of calculations for Viscosity and surface tension from oxide composition. Has anyone used these types of calculations to get useful glaze information?
Robert Coyle
BaseName LinExp Viscosity Surface Tension
Na2O 3.9 3 1.5
Li2O 0.67 3 4.6
K2O 3.31 3 0.1
MgO 0.26 1 6.6
CaO 1.48 1 4.8
SrO 1.59 2 0
BaO 1.29 2 3.7
TiO 1.44 0 3
ZrO 0.99 0 4.1
Cr2O3 1.7 0 0
W3O8 0 0 0
MnO 0.73 0 4.5
Fe2O3 1.33 0 4.5
CoO 1.47 0 4.5
CuO 0.73 0 0
ZnO 0.94 2 4.7
Al2O3 0.63 0 6.2
SiO2 0.35 0 3.4
B2O3 0.31 3 0.8
SnO2 0.67 0 0
PbO 0.83 3 1.2
P2O5 0.65 0 0
These are calculated similar to linear COE. the calculated oxide percentages are multiplied by the factor and summed.
Since both viscosity and surface tension are functions of temperature, I don't have any idea of what the units might be.
I dug these out of an old glaze software program. Can't remember which one. It had all the data as delimited text files. I don't think it is around any more.
Sep 16, 2015
Norm Stuart
It appears a Viscosity of 3 for sodium, potassium and lithium means the glaze runs more than Viscosity of 1 which is Calcium and Magnesium, both low flow oxides.
Magnesium which has such a high surface tension it crawls back onto itself away from the clay has the highest Surface Tension of any oxide at 6.6 which makes sense. Potassium which flows flat has a Surface Tension of 0.1 which seems right.
It's interesting that Lithium which has an extremely low COE has a Surface Tension of 4.6 compared to 1.5 for Sodium and 0.1 for Potassium.
Sep 16, 2015
Robert Coyle
Hi Norm
These values do sort of follow what you might expect from where the elements appear on the periodic table.
From what I have read, these values are sort of first approximations. Oxide interactions in silica melts are not simply additive. There is a dependency on what other oxides are in the melt.There are a whole lot of papers published on oxides in lower melting glasses that indicate that this type of calculation is possible. There are also a large body of information of this type on mineral formation. Unfortunately, the latter usually also includes high pressure and the presence of water.
But even crude, first order estimates might be useful from the standpoint of ultimate melt characteristics, like maybe... yes it will not craze, but will it run off the pot at cone 6 but not cone 5?
Just wondering if anyone else had looked at this.
Sep 16, 2015