Sometimes a commercial underglaze straight from the container is exactly the color you need. But what happens when it isn’t? What if mahogany brown is the right color, but not the right value? How can you work monochromatically with five values of blue if you only have three blue underglazes? Or, what if you simply want a wider selection of colors from your existing set of underglaze? I use basic color theory, general glaze mixing techniques, and lots of test tiles to answer all of these questions.
Underglaze doesn’t mix exactly the same as paint or ink, where results match an Itten color wheel, but you can still mix them together, applying color theory as a basis to experiment. You can also change the value and color temperature of an underglaze as well. I mix underglazes for clay the same as I use paint for canvases or ink for prints. I tint, shade, and mix them together to expand my color palette to meet the color needs of my work. I never feel compelled to settle for the commercially available color that is closest to what I need.
The main idea with these tests is to experiment with a commercial product and have fun with color choices. There are many different tests to blend, mix, and modify colors. The standard tests are simple, consistent, and repeatable. They’re meant to be building blocks to do more complex tests in the future. As you get more comfortable with color mixing, you can then create your own versions that best suit your needs.
The consistency or amount of water in an underglaze can vary from color to color. Factors like how old they are, how they’re stored once opened, their batch run, or the brand can all affect the thickness or thinness of an underglaze. The water content impacts the concentration of materials (specific gravity), which can affect the opacity and saturation of the color. So, it’s good to take notes about thinness or thickness of your underglazes when mixing.
Your first tests should be making visual examples of all the underglazes you want to use for color mixing (1). I use 2-inch square tiles of the clay body I commonly work with for this purpose. Using your own clay body will give you accurate samples of what the underglaze looks like fired directly from the container on the clay body you use. As always, be consistent with your method of application, always recording the results. Different colored clay bodies may affect visual results, especially with less opaque underglazes. I use earthenware, terra cotta, porcelain, and white stoneware and always have spare test tiles on hand for them all.
Test 1: Equal Parts
This is a good test to see what happens when you just mix two colors together in equal quantities. Mix two underglazes together in equal parts and see if you like what it creates. I normally use a ¼ teaspoon as my unit of measure (2). This creates enough of the mixed color to brush onto a small test tile. For best visual results, choose colors that contrast each other enough to have a noticeable effect on each other (3). Colors too close in hue or value will have changes too subtle to be visually significant.
Test 2: Value Test for Tinting and Shading
Changes in value can be made through tinting with white to lighten a color or shading with black to darken it. Tinting and shading allows you to work in a greater range monochromatically or to simply change the value of a specific color by one step.
I use the parts method for mixing underglaze since I’m measuring premixed volumes of material. The parts method is simple, consistent, and repeatable. It also allows for easy quantity changes of the successful color mixing tests. You simply use a larger or smaller unit of measurement. For this test, create a 5×2-inch long, rectangular test strip tile of your clay body (4).
In making a grayscale, each mixture will be made with different amounts (parts) of black and white. If I mix 3 parts black to 1 part white, I record it as a ratio of 3:1 in my notebook (5). If I used 1 teaspoon as the part for the test batch, I can make a larger batch using 1 tablespoon or a smaller one using ¼ teaspoon as the part. The mixing ratio is the same, 3:1, but the volume of material changes to make the amount I need.
When making a monochromatic scale, you choose one color to tint or shade and see how many discernible values you can create (6). When you’re adding the tint or shade, it doesn’t need to always be in repeated regular amounts. You’re visually mixing color, so use amounts that seem to give the best results for the colors you’re working with. Once the tile is fired, you’ll see how many of the mixes are separated enough visually to use. Not every value step will have a discernible change. If you need more steps in value, make another test strip and experiment more with mixing ratios for the value steps you still need.
Mixing note: I mix each test in its own cup, so I know the proportions are consistent and repeatable. I also label the containers to coincide with my notes. If you choose one color to act as a base and keep adding another color to the base incrementally, the test will not be as reliable. Every time you add color to the base and brush it on the test tile, you’re removing material from the cup, which changes the proportions of the base to the next added color.
Test 3: Color Progression Test
Another way to make a color lighter or darker is to mix it with a lighter or darker version of the same hue (7). To adjust my dark green, I’ll choose the lightest and darkest colors I have in the green hue for my tests. From my light and dark colors, I can use light green and shadow green. This is different from tinting and shading because a color change happens as well. When mixing light green with dark green, you get a new green color that is lighter. Whereas mixing white with dark green will only lighten the value of dark green, not create a new color or hue.
The colors you choose to mix together can also potentially change the visual temperature of the color and make it feel warmer or cooler. If you add red brown to a light brown, the temperature of the color may be a little warmer. This is good to keep in mind when choosing what colors to mix together.
When firing your test tiles, make notes of exactly how you fired them so they are repeatable. Document the clay body used, firing temperature (cone), length of firing (firing schedule), type of kiln used, firing technique, and atmosphere (electric, gas, alternative). These are all variables that can have an effect on the results (8).
If you’re like me and you make test tiles all the time, you need some kind of system to label and keep track of them all for future reference. I use a black underglaze pencil to write on the bisque tiles (see 4). Whatever numbering or labeling system you use is fine, but have something that can be easily matched to your notes. I use Roman numerals and combinations of letters and numbers for my tests.
I give names to the successful tests, record the mix in my notebook, and make a visual sample tile of it with the name on back. In the future, if I need a color from one of these tiles, I can find how I mixed it in my notebook. Develop and use a system that makes the most sense for you.
I hope you have as much fun testing to expand your color palette as I do. These introductory tests are simple, but can become complex as you get more comfortable. Build off these standard tests to create your own to further explore color. Through applying general color theory principles and standard test tile experiments, you can greatly expand your color palette with simple trial and error.
Paul Andrew Wandless is an artist, author, educator, and curator currently lives and has his studio in Chicago, Illinois. He authored the books Image Transfer On Clay and 500 Prints on Clay, and co-authored Alternative Kilns & Firing Techniques. He frequently writes for several arts magazines on a variety of topics. He’s also featured in Fundamentals of Screen Printing On Clay with Paul Andrew Wandless, available on Ceramic Arts Network. He currently serves on the Board of Trustees for Penland School of Crafts. He has also served on the Executive Boards for the National Council on Education for the Ceramic Arts (NCECA) and the International Ceramic Artist Network (ICAN).This article was excerpted from the March/April 2018 issue of Pottery Making Illustrated.