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Colored Clay Blends and Tests

To Drink, 12 in. (30 cm) in length, stained porcelain casting slip, glaze, 2018.

My journey into blending ceramic stains to create colored casting slip began as a need to find a specific blue and pink that would reference plastic hospital ware. I began using, then expanding on, axial systems as a way to create a large vocabulary of color in ceramics. I am interested in how we recognize and associate with colors, and how that has the ability to add context to objects. In Werner’s Nomenclature of Colours, P. Syme states, “In describing any object, to specify its colors is very useful; it becomes absolutely necessary. How defective, therefore, must description be when the terms used are ambiguous; and where there is no regular standard to refer to. Description without figure is generally difficult to be comprehended: description and figure are in many instances still defective: but description, figure, and color combined form the most perfect representation, and are next to seeing the object itself.” Experimenting with color options in clay gives me a wide array of visual vocabulary I can pull from to better communicate my ideas.

When doing a large-scale blend, I first determine my need for the information. In some cases I am looking for specific colors for a new body of work and other times I am just looking to expand my color library, in which case I will use things like the Pantone fashion report as inspiration. Once I determine the colors I want to use as the axes in the large-scale blend, I find paint chips that match these specific colors. I compare the paint chips to existing progression blends to see if any of my typical Mason stains match. If a singular Mason stain is not close to the color of the paint chip, I make blends of two or three Mason stains using basic color mixing theory to try and achieve the intended color.

Test Tiles

My process for blending colored clay begins with creating a test tile. I work exclusively with porcelain casting slip, so my test tiles are designed to allow for consistency within the testing process. The prototype for the tile begins with scaling down an hour-glass template previously used in a piece of mine. After scaling down the shape so the final piece will take 125 grams of casting slip to fill, I use it as a template to carve down a solid chunk of plaster to create the model for my slip-casting mold (1, 2). There is then a consideration for how the tile will be hung and if it will be glazed, so once those decisions are made, parts of the plaster model are carved out accordingly. Once the tile has been carved and sanded, a two-part plaster chain mold is made in order to cast 3 tiles at a time (3). The molds are designed to be cast solid (4).

1 The shape of the test tile is transferred to a plaster blank using a template, then the outer contour is defined using a Surform.

2 Process of carving a test-tile prototype, from start to finish: After the template for the shape of the test tile is drawn onto the form (right) and the outer contour is refined, a template is used to mark the interior opening and shallow indentation (center). These areas are shaped using loop tools and carving tools (left).

3 Pulling plaster test-tile models from the newly made two-part mold.

4 Solid cast mold for slip casting test tiles. The holes for pouring the slip are located in the half of the mold under the test tiles.

Adding Stain to Casting Slip

Ceramic (Mason) stain is added to a test batch of casting slip after first determining the water to dry-material ratio. When casting slip is mixed, a recipe can contain anywhere from 35–40% water. When figuring how much stain to add to a 125-gram cup of wet slip, I factor out the water and base my percentage of stain off of only the dry material. For my slip, this is done by multiplying 0.40×125 to get 50 grams of water, which I then subtract from the 125-gram total, leaving me with 75 grams of dry material per test cup. When testing a single stain, I usually do a progression blend from 0.5%–10% (for 0.5% stain I will multiply 0.005×75 to equal 0.375 grams of stain). This progression blend allows me to see the saturation of the color in my slip (5). Different recipes and firing temperatures affect how much stain is needed for a desired vibrancy.

5 Adding stain into a 125-gram cup of wet slip to create one tile in a color progression blend.

6 Pouring three different colored slips into the two-part chain mold to create test tiles.

Connected Quadraxial Blend

A connected quadraxial blend is a system that expands on a basic quadraxial blend, which is a method of testing four ingredients (in this case, colors of casting slip) where the perimeter is 4 different line blends of the 4 axes and the middle is a blend of each of the 4 axes, allowing the middle tile to be 25% of each corner. The quadraxial blend works on a grid, so it can be scaled up by increasing the number of points in the progression blend depending on the range of color needed.

The connected quadraxial blend takes two or more quadraxial blends and connects them through the conjoining line blend. I began this method as a way to test a full palette of colors in one blend. If each separate quadraxial blend is the same dimension (for example a 5×5-tile progression or 9×9-tile progression), then they can be connected as long as they share one or more line blend in common.

7 Connected quadraxial blend of colored clay test tiles, 36 in. (91 cm) in height, stained porcelain casting slip, 2018.

8 Pentaxial blend of colored clay tiles, 20 in. (51 cm) in height, stained porcelain casting slip, 2018.

The example above (7) is an 81-point connected quadraxial blend where 4 quadraxial blends (5×5 tiles) are connected through 4 line blends. In this example, the base colors are made up of multiple stains and are at different percentages.

Point A is 100% purple stain mix at 4% and consists of: 85% Mason stain 6319 (Lavender), 10% Mason stain 6020 (Manganese Alumina Pink) and 5% Mason stain 6306 (Vivid Blue).

Point B is 100% light blue stain mix at 5% and consists of: 100% Mason stain 6376 (Robin’s Egg Blue).

Point C is 100% pink stain mix at 5% and consists of: 100% Mason stain 6020 (Manganese Alumina Pink).

Point D is 100% yellow stain mix at 5% and consists of: 100% Mason stain 6450 (Praseodymium).

Point E is 100% turquoise green stain mix at 5% and consists of: 100% Mason stain 6242 (Bermuda).

Point F is 100% medium blue stain mix at 1% and consists of: 100% Mason stain 6306 (Vivid Blue).

Point G is 100% red stain mix at 6% stain and consists of: 50% Mason stain 6033 (Sunset) and 50% Mason stain 6026 (Lobster).

Point H is 100% violet stain mix at 5% and consists of: 90% Mason stain 6304 (Violet Chrome Tin) and 10% Mason stain 6319 (Lavender).

Point I is 100% green stain mix at 5% and consists of: 100% Mason stain 6236 (Chartreuse).

Pentaxial Blend

A pentaxial blend is a system that expands on the triaxial blend. A triaxial blend is a system that evenly blends 3 colors together, where the perimeter is 3 line blends with the middle blending together all 3 axes.

The pentaxial blend is set up using 5 axes at 100% so that the middle tile is 20% of each point (see tile 76 in figure 8). Similar to the quadraxial blend, the pentaxial blend can be scaled up and each point can consist of multiple stains at different percentages depending on the stain mix used. Figure 8 is a 76-point pentaxial blend.

Point A is 100% Mason stain 6242 (Bermuda) at 5%.

Point B is 100% Mason stain 6319 (Lavender) at 5%.

Point C is 100% Mason stain 6376 (Robin’s Egg Blue) at 5%.

Point D is 100% Mason stain 6020 (Manganese Alumina Pink) at 5%.

Point E is 100% Mason stain 6450 (Praseodymium) at 5%.

9 Double-walled whiskey sippers, 41/2 in. (11 cm) in height, stained porcelain casting slip, glaze, 2018.

Application

This process is very controlled and allows me see the full range of stain colors within my casting slip. Because the gradients of color transition subtly, I am able to see how differently a color reads depending on the color next to it, which is useful when pairing colors together.

When looking for a specific shade of a color, the interior tests in a blend are most useful as I can pick between slight differences in color. When looking to include two different colors in one piece, the perimeter of each blend is the most useful because the shift in color is generally greater, allowing for more contrast between the two.

When I began testing ceramic stains in my casting slip, I was surprised by how different the stains worked depending on the clay body (which I find to be the biggest limitation of the process). I use porcelain casting slip but have switched between multiple recipes and a commercial slip. Through testing, I have learned that not all stains show up in every recipe and the vibrancy of each stain is very dependent on the base slip recipe.

The biggest surprise in this process is the range of color achievable with just a few stains. For example, while I have developed hundreds of different colors, they are generally all made up of a few core colors including Mason stains 6020, 6306, 6450, 6600, 6376, 6033, and 6026. However, the most crucial thing I have learned from this testing is the importance of specificity when referring to color. A library of color to reference allows for choices that are more intentional and more thoughtful.

the author Allison Cochran received her BFA in ceramics from Ohio University in Athens, Ohio. She has completed residencies around Europe and at Red Lodge Clay Center. She now works as a mold maker and material developer at The Bright Angle Design Studio in Asheville, North Carolina.

This is article has been excerpted from the April 2019 issue of Ceramics Monthly.

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