|Monthly Tech-Tip |
In ceramics many technicians develop and adjust glazes by blending two, three or even four l materials or glazes together to obtain new effects
An often employed a way to develop new (usually visual) glaze effects. There are many books and web sites that cover this topic (and software to derive the recipe of the mixes). Triaxial is the most common form of blending (vs. linear, quadraxial). A factor that makes this type of blending easy-to-do is that corner or end points can be mixed as slurries (having equal specific gravities) and poured together by volume. Typically triaxial blend corners are labelled A, B and C. Mixes between corners, for example A and B in the photos below, are termed 3A-1B (75% A, 25% B), 2A-2B (50% A, 50% B), 1A-3B (25% A, 75% B). Mixes in the center of the triangle contain all three corners, they are 2A-1B-1C, 1A-2B-1C and 1A-1B-2C.
In its most random instance, triaxial corner points are chosen from existing glazes that are unsuitable or extreme in some way (e.g. too matte, runny, not melted), with the hopes that somewhere within the blend will be a new interesting effect (choice of corner points is thus the key factor in the likelihood and finding a result). Materials (e.g. feldspar, silica, clay) are often blended to find the percentages at which they produce a good glass. In the most directed approaches, blends are done to fine-tune color, matteness, melt fluidity, etc.
Triaxial blending is about recipes. But people who know glaze chemistry (tempering that with knowledge of materials and minerals) employ blending techniques much less, often as a final step to fine-tune a recipe (after it was developed by targeting or adjusting a chemistry). They see the discovery of glaze effects as much less a matter of chance and much more likely by empirical methods. At each step they rationalize the actual fired results to the expected outcome, learn, then adjust and repeat until the desired effect is achieved. Each project becomes not only an opportunity to hone prediction skills but build abilities to explain why things happen and how to diagnose problems. As you might expect, at Digitalfire we promote this method of glaze development rather than triaxial blending.
The result is much less predictable than for blending existing known glazes, these reservoirs contain the runoff if the melted result is excessively fluid.
A is a matte white, B is Rich Iron Red and C is a glossy white. Recipes 1 and 2 are 75% A, 6 and 10 are 75% B, 9 and 12 are 75% C. 3, 4 and 5 are 50% A, 3, 7 and 11 are 50% B. 5, 8 and 11 are 50% C. This blend was done in 1977 in the lab at Plainsman Clays.
Matte glazes have a fragile mechanism. That means the same recipe will be more matte for some people, more glossy for others (due to material, process and firing differences). In addition, certain colors will matte the base more and others will gloss it more. It is therefore critical for matte glaze recipes to have adjustability (a way to change the degree of gloss), both for circumstances and colors. This recipe is Plainsman G2934 base matte with 6% Mason 6600 black stain added. It has been formulated to be on the more matte side of the scale so that for most people a simple addition of G2926B (M370 transparent ultra clear base recipe) will increase the gloss. That means users need to be prepared to adjust each color of the matte to fine-tune its degree of gloss. Here you can see 5:95, 10:90, 15:85 and 20:80 blends of the matte:gloss recipe bases.
These 10 gram balls were fired and melted down onto a tile. The one the left is the original G2934 Plainsman Cone 6 MgO matte with 6% Mason 6600 black stain. On the right the adjustment has a 20% glossy glaze addition to make it a little less matte. Notice the increased flow (the ball has flattened more) with the addition of the glossy. In addition, while the percentage of stain in the one on the right is actually less (because it was diluted), the color appears darker! Tuning the degree of matteness when making color additions to a base is almost always necessary to achieve a glaze that does not cutlery mark.
Chemistry vs. Matrix Blending to Create Glazes from Native Materials
Is it better to do trial and error line and matrix blending of materials to formulate your glazes or is it better to use glaze chemistry?
Glaze chemistry is the study of how the oxide chemistry of glazes relates to the way they fire. It accounts for color, surface, hardness, texturem, melting temperature, thermal expansion, etc.