Scratching the Surface: The Terra Sigillata Clay Tile Paintings of Jenny Mendes

Plus, a great terra sigillata recipe!

terra sigillata

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:

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terra sigillata

No slab roller? No problem! All you need are two same-sized sticks and a rolling pin!

terra sigillata

Cut the slab on the surface where it will dry. This helps to minimize warping.

terra sigillata

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.

terra sigillata

Clean up the edges of the bone dry tile with a sponge and then add a base coat of terra sigillata.

terra sigillata

Draw/carve into the clay with a sharp Exacto knife to create the lines.

terra sigillata

Add details to the drawing in a different colored terra sigillata, almost like filling in the spaces of a coloring book. Layering colored terra sigillatas adds depth. Ghost images can be preserved by painting over the line so that it is covered, but still there.

terra sigillata

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.

terra sigillata

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

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

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.

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.

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

**First published in 2013
  • Okay, now I’m confused about making Terra Sig. I thought you were supposed to siphon off the layer just below the yellow water, the middle layer – according to some articles I’ve read. Or siphon off the yellow water and then go back for the next layer – which is the Terra Sig. Is that wrong? I’m new to Terra Sig as well and find the wide array of recipes and instructions in various books and online articles very confusing.
    I made red Terra sig and am having trouble getting it to the right specific gravity, and in getting enough sheen when burnished. Help!

  • Callie B.

    I can maybe help with the horsehair question. The way I’ve seen it done is to apply the sig to leather hard or bone dry clay, and yes, you do your first firing to a higher temp to impart strength to the clay. You then use the lower tempt to apply the horsehair.

  • to alleviate warping: condition your slabs of clay between plaster board ( cut in 2′ or 4′ square bats).
    Make a stack: alternating plasterboard/clay/ plasterboard/clay and so on. The clay slabs are dried uniformly until you are ready to size your tiles accurately. We have found this method very successful when preparing clay for our hand-made tiles when making tile panels

  • The surest way to avoid warping for tiles is to put them on a wire rack to dry so both side get equal air time. If you are working on wet or leather hard tile, the bottom needs absorbent material beneath to equal the air drying on top to avoid warping.

  • Hi.
    I would apply the sig to bone dry clay. You will have the best results, and it will adhere best. I don’t know about your second idea, but you could always try and see what happens. Regarding horse hair, I don’t really know what that means…….sorry!

  • Jenny,
    Finally sharing your “secrets”- I’ve been keeping up with you on facebook and etsy. Everytime I open a magazine I see you there. Glad your having such success. Your images are quite fun. Good luck with your sales. Pat

  • Thanks Jenny!
    Yes, Pat it does need to be fired again. Looks like Jenny fires her patina’s/underglazes to ^03. My second firing is to ^04 but maybe I’ll try ^03. You will also need to burnish your sig to get a nice shine or it will look dry.
    After I brush on and rub off the Patina/underglazes I will go over my work with a wash of 1 part soda ash to 6 parts warm water. And/or 1 part 20 Mule Borax to 4 parts warm water. These washes can produce an aged and wet look. Borax will also give off small spots or specks of color. As with everything, test first.
    I had the great fortune of being taught by Joe Pintz who was a graduate student of Pete Pinnell’s.
    You can see what I’m talking about on my web site.
    Thanks again Jenny and too Arts Daily for the information, nice work!!

  • Can terra sig be made with higher firing clays like ^6 or ^10, and does the higher firing destroy the effect in any way? I remember looking into this years ago but don’t remember whether it was mainly used at low temperatures, or if so, why.

  • Sandra O.

    I will like if somebody has a recepi for a black metAL GLAZE 04/06< I had a recipe from Dina Wilder R< the base was black TS.

  • Linda,
    I have put a clear glaze over the terra sig before, and the results can be great, but will look very different. Colors will change and thin spots might disappear into the glaze, but that could be a good thing. You should definitely try it, and see what you think!

  • Jenny,
    Do you ever use this technique on platters or more functional pieces?
    Do you ever seal your pieces with a clear glaze (over the terra Sig.)?
    Your process looks very interesting.
    Thanks for sharing. Linda

  • Robert B.

    Cool stuff- I like the images! My experience with terra sig is that glaze will usually burn or wash out the image because the sig is usually so much thinner than a slip. I do not have tons of experience with it, but that is what I have found when I have tried it.
    I like the black underglaze technique! I have pit fired terra sig quite a bit, but want to switch to electric firing and do more detailed surfaces, so this article came right in time! Thanks…
    Ditto on the high fire comment- the luscious terra sig surface diminishes in the high fire… My understanding is that in the high fire the sand and grog in the clay pushes to the surface and takes away the burnished surface…

  • Could someone clarify what “Black Stain” to use to achieve black terrasigilata? or any other colorant to get black?

  • Okay, I’m brand new to Terra Sig. Just got a wheel and I’m throwing basic forms. I have a white versa clay which has a range of 05 to 5. I could use some basic info. I assume that I apply the sig to the bonedry greenware, then fire to 05–then I’m done right? Or, can I fire the greenware to say cone 2, then apply the sig and then fire it to the lower temp of 05? Third question. If you want to do horse hair on top of fired sig, is the pot with the sig brought up to say cone 05, cooled, then refired to the much cooler temp of 020 for the horse hair technique? Any info from anyone would be sooo appreciated. Thanks AMDG T Meisling

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