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Published Mar 16, 2020

Drawing/painting on clay is something I have experimented with from time to time with limited success. So I always have deep admiration for those who can do it well.

Jenny Mendes is one of those artists. Of course, not even Jenny can explain the mystery of how her imagery makes it out of her subconscious and onto her clay tile paintings. But she can explain the technical details of scratching her drawings into moist clay and layering various colors of terra sigillata to create her rich illustrations. That's exactly what she does in today's post. Once you have the skills, you can reach deep down beneath the surface and see what imagery dwells in your subconscious! - Jennifer Poellot Harnetty, editor

Drawing with Terra Sigillata

I love to draw on anything but especially clay. Discovering the pleasure of drawing on and into a bone dry clay tile was illuminating for me. This soft subtractive way of drawing leads me into my subject in a way that drawing on paper never has.I don’t think my process is the most exciting thing to watch. Probably the [most] interesting [part of my process] is when a mysterious image comes to me from where I know not. I can’t explain that part in a how-to, but here are the technical details.

No slab roller? No problem! All you need are two same-sized sticks and a rolling pin. Cut the slab on the surface where it will dry. This helps to minimize warping.

The tile is then dried between two sheets of drywall. Make sure it isn’t sticking, and then leave it alone until it is dry. The less you mess with it the better. Clean up the edges of the bone dry tile with a sponge to ensure that there are no sharp edges. Then add a base coat of terra sigillata.

Draw/carve into the clay with a sharp Exacto knife to create the lines. Add details to the drawing in a different colored terra sigillata, coloring book style.

Layering colored terra sigillatas adds depth. Ghost images can be preserved by painting over the line so that it is covered, but still there.

After bisquing to cone 06, apply a layer of black underglaze and then wash it off. Lines are enhanced by the black that remains in the recessed areas, and additional colored details are added to the composition if needed. Even though I know what the line drawing originally looked like, it is still exciting to see what it looks like when the black is washed away and the lines darken. The nature of the original line (was it made with a soft touch, or was it shallow, or deep and sharply cut) will determine the final look of the piece. 

Refiring the tile to cone 03 deepens the colors, and adds richness to the surface.

After bisquing to cone 06, apply a layer of black underglaze and then wash it off. Finished tile with lines enhanced by the black underglaze remaining in recessed lines.

Making Pete Pinnell’s Real Authentic Lip Smackin' Smooth Easy Terra Sigillata

In a 5 gallon bucket, put 28 pounds (28 pints or 31/2 gal.) of water. Add 14 pounds dry clay. XX sagger works well for white base, RedArt for red. Add enough sodium silicate to deflocculate (a few tablespoons). For red clays use 2 teaspoons sodium silicate and 1 tablespoon soda ash. Allow to settle. Overnight is average. Less plastic red clays (such as RedArt or fire clay may require only 6-8 hours, while very plastic clays like XX Sagger or OM4 ball may take up to 48 hours). Syphon off the terra sigillata from the top (this is the terra sig) without disturbing the sludgy mixture below. Throw the rest away; do not reclaim.

Terra sig is best when the specific gravity if about 1.15. Useful range is 1.1 - 1.2. Specific gravity is measured by weighing out 100 grams of water, marking the volume, and weighing the same volume of the sig. Divide the weight of the sig by 100. If too thin evaporate. If too thick allow to settle longer. Apply sig to bone dry greenware and buff. Pete uses "patinas" of 1 gerstley borate + 1 colorant as a thin wash over bisqued sigs, applied and rubbed off. Works on textured areas.


Color suggestions to 1 cup liquid terra sigillata:

white = + 1 tsp. Zircopax or tin

off white = + 1 tsp. titanium dioxide

green = + 1/2 tsp. chrome oxide

blue = + 1/2 tsp. cobalt carbonate

black = + 1 tsp. black stain

purple = + 1 tsp. crocus martis


terra sigillata
Jenny Mendes has a variety of terra sig on hand in her studio.


To learn more about Jenny Mendes or to see more images of her work, visit


**First published in 2013