Slip decoration is among the earliest of pottery surface-decoration techniques, and some fine examples of slip painting date back at least 5000 BC in Egypt, Anatolia, and other locations in the Middle East. Among pre-dynastic Egyptian ceramics we even find examples of raised-relief slip-trailing. Intricate slip-decoration with transparent glazes was the surface decoration method of choice during the Byzantine Empire, and the technique traveled into the Balkans and Eastern Europe via Byzantine and Ottoman Imperial expansion.
My father was full-blooded Czech, and I have always gravitated towards the intricate surface decoration in Eastern European crafts. Around 1980, I started doing slip-trailed and feather-combed slip decoration in my studio, Railroad Stoneware, in Blue Lake, California, as a diversion from production utilitarian ware. I would most likely have transitioned entirely to one-of-a-kind slipware, but in 1985 my wife and I made the decision to attend graduate school in Massachusetts and I shut down my studio in California. For the next ten years I abandoned slip-decoration in favor of colored clay work, but took it up again during my first few years at the Appalachian Center for Crafts. Some of the examples below are from 1980 to 1985 in California, and others from 1994 to 1998 at the Craft Center.
Scroll down below the images for technical information. Click on the thumbnails to see a larger image.
I use a basic white porcelain slip similar to the STA Decorating Slip (click here for the recipe PDF), and color it with ceramic oxides (as specified on the same PDF). Normal cone-10 porcelain bodies are fluxed with potash spar, while all-temperature decorating slip recipes like the STA slip are adapted by replacing part of the potash spar with a combination of midrange flux such as nepheline syenite and lowfire flux such as Frit 3195, improving slip adhesion throughout any firing range. Most problems with slip separating from the surface occur as the kiln passes through early red heat and the claybody and slip begin shrinking at different rates. The addition of a very low-melting flux (usually either borax or a calcium-borate frit like Ferro 3195) improves the bond at the interface between slip and body just as firing shrinkage begins. Also, the slip is deflocculated, which greatly decreases drying shrinkage and thus reduces chances of the slip separating during drying or firing. All of the pieces pictured above were reduction-fired to cone-10 in a downdraft gas kiln.
Most of the slip-trailing seen here was done with rubber ear-syringe bulbs cut back at the tip and equipped with trimmed basket-ball-inflating needles and a short length of very fine plastic tubing. The inflating needles have the hole on the side near the end, which won’t work in this case. To adapt basket-ball-inflating needles for slip trailing, straighten out a paper clip, insert it all the way into the needle from the back end, and use wire cutters to snip off the end including the side hole. The wire keeps the tube from collapsing. This setup will work with just the modified inflating needle affixed in the ear syringe bulb, but is less likely to gouge the clay surface if equipped with a short extension of tubing, and 1/16″ inside-diameter medical I-V tubing is ideal. Lacking that, very small heat-shrink tubing (available from electronics or auto parts stores) will also work well.
Currently, my favorite slip-trailing vessels are the plastic bottle applicators made by Xiem Studio Tools. At their website, click “Precision Applicators” on the left and scroll down to select the ones best suited to your needs. The plastic bottles are far less expensive than ear syringe bulbs or Xiem’s rubber-bulb applicators, equally effective, and far easier to fill, use, and clean. Slip decoration often involves switching back and forth between many colors of slip, and that gets very expensive with multiple rubber bulbs. With the Xiem plastic bottles, you can inexpensively purchase multiple bottles, caps, and precision tip sets to suit your needs.
There is some misunderstanding about the technique known as feather-combing. The name comes from the combed pattern’s resemblance to a feather, not from the use of a feather as a tool to manipulate the slip. Any flexible, fine-pointed tool will work, and the objective is to create enough friction to pull the liquid slip colors in order to attain the classical combed effect, but without digging into the clay substrate beneath. My favorite tool is a short length of 50-pound-test monofilament fishing line affixed to a thin wood dowel handle with a piece of duct tape. It works best if the monofilament extends from the dowel about an inch and a half. If you find that the tip of the monofilament does not pull the slip colors satisfactorily, hold the tip close to a lighter or torch flame and melt the end to form a tiny ball.