Once I’ve finished painting my leather-hard jugbirds with coloured slips I leave them to dry. The final step before the bisque firing is to coat unpainted areas, usually the foot, with terra sigillata. It makes a fine, smooth surface.. think Roman Samian ware.. and I like the look as a contrast to the super shiny glaze finish of the rest of the pot.

Realizing I was almost out of my supply of terra sig, there seemed no better time than now to mix up some more, and to document the process. As I weighed out the Redart Clay powder and added water and dissolved Calgon I was once again grateful to the late Gail Carney, ECIAD ceramics technician, for this so-easy low-tech method. You can’t buy ready-made terra sig, as far as I know, so sharing this technique might be useful.

Redart Terra Sigillata

Redart Clay powder 2 kg

Water 8kg

Calgon water softener 3gm

Dissolve calgon in a little warm water, mix with the clay and water, sieve and leave for an hour. Then pour into another bucket every twenty minutes, discarding the bottom sludge, until there is almost no residue. The next day is too late to continue. The watery result can be left to evaporate or put in a large pot on the stove to bubble away the excess water.  Stir and apply with a brush to bone-dry ware in several thin layers. Pots can be dipped in terra sig or sprayed. If it is too thick, like a slip, it may spall off.

In these photos you’ll see me adding the Calgon/warm water mixture to the clay and water, and that I seived said mixture and LEFT IT FOR AN HOUR.

At that point I carefully poured it all into another bucket and you’ll see the sludge left in the bottom of the first one. I dumped the goop into the back of the yard.. don’t put it down the sink!

Thereafter I decanted the liquid from one bucket to the other about twelve times, twenty minutes or more apart. Each time there was a deposit of larger particles but nowhere near the amount of that first pour. At the end of the day I left it. Two days later you can see that I have a large bucket of super fine terra sigillata. Sometimes I have boiled away excess water when I’m in a hurry but this batch seems to be about right and I can leave it uncovered for a few more days.

I’ve found that most clay powders can be used to make terra sigillata. Here is a recipe for a white one:

Goldart Terra Sigillata

Goldart Clay powder 500gm

Water 1 kg

Calgon 3gm

Good off-white and a basis for other colours, usually stains.

I have used red and white terra sig with stains added, on parts of stoneware pots in soda firings. It gives a good contrasting GLAZE finish next to the usual sprayed slips on my jugbirds.

The first photo is of some more recent pieces on which I’ve used terra sig. The basket is my version of a Verwood, Dorset historical one.

The signature piece for my 2003 show ‘Ornithikos’, at the Gallery of BC Ceramics, was this Rooster. Most of his surface is terra sigillata.