How I make my black slip

This post will detail the steps involved to mix up my black slip I use for all of my black & white sgraffito forms. It's fairly simple if you use a white clay body (preferably without grog to keep a smooth consistency). I fire this slip to cone 5/6 in an electric kiln. The temperature it can be fired to depends on the clay you use as the base of the slip.

Materials Needed:

• white clay trimmings dried out completely to bone dry
• black mason stain (6600 or similar)
• digital scale
• plastic container with lid (large yogurt container is what I use, screw on lid a bonus)
• emulsion blender (can alternatively use a whisk, but it won't be as consistent throughout)
• water
• 80 mesh sieve (optional)

Steps to Make:​

1. Break up white clay trimmings to pieces smaller than 0.5" x 0.5". You want this clay COMPLETELY dried out to bone dry to ensure your slip is the same consistency throughout. If you have a mixture of bone dry, leatherhard, and hard leatherhard trimmings, you will end up with lumps.
2. In your plastic container, weight out 500 grams of bone dry clay trimmings. You will need at least an inch or so of space left at the top to allow for water, mason stain, and mixing without making a mess. 500 grams will yield about 1 quart of slip.
3. In a separate small container, weight out 100 grams of black mason stain (6600 is the color I use). This number was calculated from adding 20% mason stain to the clay (500 x 0.2 = 100). Scale this number up depending on how much slip you want to produce.
4. Sprinkle the black mason stain on top of the dry clay trimmings.
5. Fill up the container with clay trimmings & mason stain with water, enough to have all materials submerged. You will see some bubbling as the water is absorbed by the clay. The water level may fall as more water is absorbed & more water may need to be added. This step can be a little messy! I recommend pouring water slowly from a pitcher so your mason stain doesn't go everywhere as you add the water.
6. Leave this to sit overnight (8-12 hours) so you know all water is thoroughly absorbed by the clay.
7. After letting it sit, you may be left with some clear water on top, I try not to have more than 0.5" of water to get my slip to the consistency I like. You can use a sponge to carefully soak up some excess water.
8. Use your emulsion blender (or whisk) to thoroughly mix the slip. This is going to change the color of your slip as the black mason stain gets integrated throughout the entire container. You want to make sure you are getting the blender down to the very bottom and sides, otherwise you will have 'pockets' of slip that are white and the rest will be black.
9. Depending on how you plan to use the slip (adding to leatherhard pieces for drippy effects, painting on, slip inlay, sgraffito, etc), you may want to add more water if it's too thick or leave the lid off for a few hours to let it thicken up. The good thing about using slip as opposed to underglaze, you can add/remove water to get the desired thinness/thickness and it won't have any effect on the intensity of the black color on the end result.
10. Optional: To ensure a smoother consistency, you can put the slip through an 80 mesh sieve once. I do not do this step since the emulsion blender does a great job for me on it's own.

Other things to keep in mind:

• The color of your slip at a wet stage will not exactly match the end result. It will intensify during firing. It will look more like a charcoal grey at a wet stage.
• Always shake your slip before applying to pieces. The clay particles will settle in your container overnight and you will see water on top the next time you use it. Shake it up and decided if it needs more water. Add water and shake again until you get your desired consistency.
• The black slip can be placed on the bottom of your pieces that will have direct contact with the kiln shelf. Unlike some underglazes, your slip should not stick to the kiln shelf since it is really just a black version of the clay you use already.
• When applying the slip to pieces, I like to mix my slip up to a thick cream consistency and paint on 2 thick even coats to ensure it doesn't have any streaking.
• You can use any variation of this mason stain ratio to get a lighter/darker grey. 20% black mason stain will give you a black color, anything less will give you a light to dark grey.
  • 15% stain may yield a charcoal grey color
  • 10% stain may yield a medium grey color
  • 5% stain may yield a light grey color
• It's easiest to add your mason stain to the weighed out dry clay because it's harder to get the percentages accurate when the wet slip can have varying amounts of water content. You may need to do a little bit of experimenting to figure out the right ratio by volume (for example, 1 qt of wet slip needs 100 grams of black mason stain)