Compare Slips, Engobes or Colorants

So you are ready to explore the world of color and clay. How exciting! There are so many choices in the world of ceramics and pottery, that creativity is limitless. Hopefully this brief explanation of the different colorants available to the clay artist will get those juices flowing. Included are recipes for the really adventurous; otherwise there are commercially made products available as you explore this aspect of creating with clay.

Slips

Slips are a liquid clay that can be used for casting plaster molds or for coloring clay bodies. Besides being used for casting, they are usually applied to wet or dry greenware. Slip is most commonly used to refer to any clay that is liquid. Slips can be colored to enhance decoration of final product. Underglazes are liquid clay with colorants.

Engobes

Engobes are similar to slips but have a lesser proportion of clay to colorant and can often be used on bisqueware. Some modern day commercial underglazes are engobes

Now What?

Slips and engobes can be colored with stains or colorants (recipe below) that have been produced for this purpose. Color may not show true until fired and then sometimes, color will be affected by the temperature it is subjected to. The hotter the temp, the more change possible in final results.

So what can you do with the ability to color your own underglazes and engobes? (Or you can use commercially made)

1. Color your slip and produce bisque already colored (this
can stain the mold as well). It takes more colorant to color slip for casting molds than for painting/decorating.

2. Color small amounts of slip and roll around the inside of a
mold - not covering all of the surface, giving a marbled effect to the surface (this can stain the mold as well).

3. Slip trailing a design on a pre-made piece of greenware
(and sometimes bisque);

4. Combing different applied colors while wet to create
designs.

5. Layering colors to increase contrast.

6. Marblizing by drizzling various colors on a surface then
using tool to swirl them around

7. Color small amounts of slip and apply to suitable pre-made
item by dipping, sponging, rolling, brushing, detailing.

8. Apply to the surface of a un-fired glaze. Cover the
un-fired glaze surface with a coat of gum solution or Karo syrup to prevent disturbing the glaze.

9. Apply colorant on top of suitable fired glazes creating
many effects. Mix colorant with alcohol instead of water to prevent running. Creates an interesting rough surface.

10. Create your own colors by mixing colorants together. Always make a test chip and keep records of your
mixtures for future reproduction.


Colorants

Colorants are made by mixing various oxides and carbonates in some slip or opacifier (frit), firing them and then grinding them into a very fine powder. Being super fine allows them to pass through an airbrush. These colorants are then used to color slips or engobes. These colorants are also often used in glazes. Being chemically created, there are almost limitless color options.
The most common use of stains/colorants is in making colored decorating slips. Slips (underglazes, or engobes, all being basically colored clay) do not melt in the firing and the individual components chemically interact.

The base could be a slip made from the clay being used if the clay is not dark (any grog should be sieved out to prevent a rough surface). This assures compatibility in shrinkage rates. A premixed dry clay body could be purchased.

A prepared low fire white underglaze or engobe could also be used up to Cone 6 although that would be more expensive. For a low fire base, a simple 50/50 mix of ball clay and talc would work. A very simple Cone 10 base would be equal parts of kaolin, flint, ball clay and feldspar. Additional flux should be added to all except the 50/50 mix.

Generally stains can not be successfully applied to a surface as iron oxide might be to emphasize texture without at least adding a flux to make them "stick" as noted above. Additionally, it is usually difficult to apply enough straight stain to get the intensity without adding it to a slip clay or gum solution so as to be able to apply more actual stain

Purchasing ready-made commercial engobes and underglazes is by far a time saver. But for the adventurous, Below are recipes to make your own engobes/underglazes. Usually the ingredients can be bought at most pottery or ceramic suppliers.

Click here for a printable pdf of the engobe recipes.