The Ceramic Series: The Kiln, Sgraffito and Resists (Part One)

Having a large kiln is a blessing and a curse. The blessing is that you can do tons of pieces at once. The curse is of course that the kiln needs to be full in order to make economic sense -- it burns a lot of electricity. So in the second half of November and first half of December I worked to fill orders, make pieces for my on line shop and tiles for our new guest room. I got a full oven of pieces bisque fired before the end of December I still had pieces that had been bisqued but not glazed from the summer - the late season was simply too busy for me to work in the studio. Here are a few of those older pieces, before they got glazed (the parts that are darker will be celedon/turquoise after the glaze firing):

These designs were made by painting a slip, or engobe, on the leather-hard surface of the thrown pieces. The designs were painted on then carefully sculpted with a sgraffito knife, a technique which literally scratches away the clay. The result is that the designs are slightly raised.

In the week since getting back from the States, I have been bouncing between a cold, jetlag, and getting pieces glazed. The oven is filled to the absolute rim and is firing as I write. Another full two loads are waiting to be glazed and fired as well.

You can fire triple the amount of pieces in a bisque firing that you can in a glaze firing, because you can stack the pieces carefully on top of each other with a bisque firing. But glazed pieces cannot touch each other, and while glazing it's important that no glaze remains on the base of the piece. Otherwise it will stick to the oven shelf, ruining the shelf, breaking the piece, and causing painful hand cuts -- I have had a few of them in my time!

As the oven was warming up, I wanted to take advantage of the heat in the room radiated by the kiln and worked on some previously bisque fired pieces. These pieces are plain, not colored or painted in any way.

I used liquid latex to paint a pattern onto the plate. This is called a resist. Resists are areas of the surface which should remain unglazed, uncolored, untouched. I am using paint-on latex here. It dries into a rubbery substance. You then glaze the piece and remove the resists -- the area underneath the resist will be smooth and unglazed, and recessed from the glazed surface.

An alternative to liquid latex is to use wax. Both the latex and the wax have their advantages. The wax stays on and simply burns away in the kiln. The latex gets removed beforehand, which means you can do multiple layers of colors and glazes with the latex. With wax, it's just the one resist and that's it.

I should be using wax for these resists, since I am only doing one single uncolored layer, but I am out of it, so latex it is.

Both the plate and the rice bowl will be glazed soft white -- so they will be white on white when they are finished -- white glaze with a white unglazed design.

I now need to mix the glaze and glaze the pieces. The resists will get peeled off and the piece goes into the kiln for firing.

Here is a more detailed example of a ceramic resist. I made this little fish soap dish a while back. I am glazing it with my standard glaze with 2% cobalt carbonate added to it. The cobalt carbonate should give the glaze a soft blue color.

But before I glazed the piece I wanted to make sure that the rim of the fish soapdish would not get glazed, and remain white and raw, so I coated it with the liquid latex.

I then glazed the piece and peeled off the latex:

You can see that the surface where the soap would sit is glazed (not fired yet of course) and the edge is raw.

I will be back when I open the oven in a couple of days with a round up.