Sgraffito and Terra Sigillata: A Great Combo for Intricate Designs Alex Pratt

Mixing and Applying Terra Sigillata 

I find that terra sigillata allows for more intricate detail than slip or underglaze, and also tends to feel less textured when finished (which I prefer). I make terra sigillata in large batches. To stain the terra sigillata black, I add about 1–1½ teaspoons (4.9–7.4 ml) of Mason 6600 Best Black stain to two cups (480 ml) of terra sigillata. I do not ball mill my terra sigillata, nor do I burnish it after applying it to the pot. Glaze adheres best to non-burnished terra sigillata.

The terra sigillata must be at the proper consistency for the technique to work. If it’s too thin, too many coats are required to get an opaque coating, potentially weakening the pot. If it’s too thick, it’s likely to flake off the pot. Specific gravity of 1.15–1.17 works well for the purpose of this project. If the terra sigillata you are using is too thick, add water a little at a time, mix it up, and weigh it again until the specific gravity reading has lowered to the appropriate level. If it’s too thin, place the liquid in a wide shallow bowl and set it aside to let some of the water evaporate. This can take several days to a few weeks. 

Brush three coats of black terra sigillata onto the bone-dry pot using a mop-style brush (1) and allow the pot to dry for a full day before beginning sgraffito. Tip: Investing in a high-quality mop-style brush is well worth it. Cheaper brushes will shed bristles while you brush on the terra sigillata, leaving a noticeable mark. I prefer to use a synthetic sable Winsor & Newton mop brush.) 

Carving Sgraffito Designs 

Lay down a piece of thick foam large enough to cushion the vase, and lay a piece of soft cloth on top of this. A soft t-shirt cut up into pieces works well. Begin by laying out the elements of a design that are meant to be seen as being in front of other elements—in this case, the vine shapes that appear to encircle the vase. To create the vine shapes, use a template to create long, clean, arcing lines—I make my own cardstock templates using a die-cut machine and its design software. Templates and other tools allow for the precision that this particular motif needs. 

Lay the template smoothly against the surface of the vase and use a needle tool to run along the surface of the template (2). Because of the outward swelling of the form, the template will need to be adjusted periodically to stay flat against the side. Criss-cross these vine lines several times. The curves are intentionally placed so that they seem to disappear around the side of the form from any vantage point. 

Next, move on to the sunburst image, gently using a compass to create four concentric circles—two for the inner ring and two for the outer ring (3). Finish with one wider final circle around the entire image that will serve as a frame for the sunburst image. Add a few large, vertical spiky leaf-like shapes and create another large, wide black ring around this area using the compass and creating another wide white band to set it off. 

I finish with one smaller white circle with a narrower black ring, surrounded by a white band above the sunburst image. 

Caution: Always wear a NIOSH-approved respirator when incising a bone-dry pot, and work in a well-ventilated area. Be conscious of the dust generated during the incising process and periodically vacuum it up with a vacuum cleaner fitted with a HEPA filter—do not sweep it up, as this can cause the dust to become airborne. 

Alex Pratt lives in Dearborn, Michigan. He has a BFA from the University of Michigan and has worked as a production potter and teacher. He works out of a basement studio in the home that he shares with his partner, two cats, and way too many books. To see more, visit alexprattpottery.com.