Custom glaze color formulation
Challenge: Glaze colors change dramatically when fired in the kiln due to physical changes and chemical reactions. Glaze colors cannot be mixed by eye the way paint can.
Solution: Create a palette of repeatable color formulas.
Step 1. Fit glaze to clay
Glazes can crack (AKA craze) and develop pinholes if they aren’t formulated and fired properly. This can impact glaze strength and durability.
Currie grids (arrays of different ratios of glaze ingredients; shown on the right) were used to find the glaze formulas with the best characteristics.
Flat tiles (below) were coated with the most promising formulas to test for crazing and pinholes, and standing tiles were painted to test for excessive melting. Since I plan to use this glaze for painting, drips and runs are not desirable.
Step 2. Make concentrated stock solutions for each mixing color
A basic palette of stock solutions, similar to a painter’s palette, was made with the aim of mixing a wide range of colors. I started with mason stains in light and dark yellow, orange, warm and cool red, light blue, and warm and cool dark blues. White, black, and brown were added, as well as two special effect whites and some mineral colorants.
Step 3. Develop a range of values
Linear blends (with stepwise concentration changes) were created for each base color. Most blends ranged from 1-10% colorant, but some colors, especially cobalt, were very strong and required less colorant.
Step 4. Create secondary colors and neutrals
Triaxial blends (mixes of three colors) made a variety of greens, purples, oranges, browns, and grays. Blended colors like these are more subtle and dimensional than single pigments, and combine well with the base colors in a project.
Tip: Keep good records
The base colors were each assigned a letter for record keeping purposes. Each tile was assigned a specific ratio of the three colorants used in the triaxial blend and arranged in a triangle during color mixing. The ratios were also painted on the back for future reference.
Step 5. Build an array of colors
To avoid repeating linear blends at the edges of the triaxial blends, I arranged the triaxial triangles to meet at their corners, forming hexagons of color. This chart helped me keep track of which triaxial blends had been completed. A few are still in progress.
Results: So many colors!
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Secondary colors
Triaxial blends produced a lot of oranges, greens, and brownish purples. This is just a sample.
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Blue is a strong glaze color
Even at half concentration the blues easily overpowered the reds, making it hard to get purple. I’ll probably need to introduce a purple stain to get the color I want.
Current color palette
This looks like a lot of colors, but it’s only about a quarter of the original test tiles. Purple and violet need more representation, and I’m still looking for an intense red, but overall I’m very happy with how this turned out!
Pure pigments are arranged in a horizontal line on the bottom left. Similar hues are arranged vertically across the rest of the board, with the darkest shades at the top. This makes it easy to choose colors by value as well as by hue.