Question: how to do sgraffito on clay?
Answer: Sponge on Black Velvet Underglaze. ... 
Select or draw a design. ... 
Scribble on the back of the design with a soft pencil will help the design transfer. ... 
Attach the design to the clay and trace. ... 
Remove the paper to see the image. ... 
Outline the image. ... 
Scrape away areas of the design to expose the clay.