Sgraffito,(via Wikipedia) (Italian: [zɡrafˈfiːto]; plural: sgraffiti; sometimes spelled scraffito) means “applying to an unfired ceramic body two successive layers of contrasting slip, and then in either case scratching so as to reveal parts of the underlying layer.”
In this case, I use a porcelain mix clay – it’s not pure porcelain, but a clay mix with porcelain in it, which makes the clay easier to work with than porcelain, yet still fires to an almost-white color. When the mugs are not quite dry, I dip them in black slip – clay that’s thinned down to a thin pudding-like consistency mixed with things such as red iron oxide, manganese dioxide, and cobalt carbonate to color it black. Then after that dries out a bit, I carve a design through the black slip, allowing the white clay underneath to show through. Here’s a pic of 2 mugs with a design I created using a book published by Dover titled European Folk Art Designs.
And here’s a pic of mugs with my favorite spiral design. At this point, the black slip looks brown and the white clay looks more cream or light-tan. The mugs are still just a bit damp and are covered with plastic so they dry out very slowly.
Once they are completely dry, the mugs get bisque-fired at a lower temperature, then they’re dunked in clear glaze and fired again at a high temperature. During that final firing, the black slip turns black and the white clay turns white. Here’s a pic of a mug I made a couple weeks ago.
I’ve got 6 of these mugs available for purchase on my website. More to come soon! Carving designs into my ceramics is lots of fun for me!