Sgraffito is drawing by removal: a contrasting slip is applied over a pot and a design is scratched through it so the clay beneath shows. It is one of the oldest decorating techniques in ceramics and one of the very few that needs no special equipment at all.
How it works
A dark slip over a light body, or the reverse, gives two tones. Scratching through the slip exposes the body and draws a line in the other colour. Because the line is cut rather than painted, it has a crispness and a slight relief that a brush cannot produce, and it is why sgraffito ware looks the way it does.
Timing is everything
The slip goes on leather hard and the scratching happens when the slip has lost its shine but the pot is still leather hard. Too wet and the tool drags a smeared, ragged line; too dry and the slip chips away in flakes rather than cutting. The workable window is a few hours, which is why sgraffito is usually done in one sitting.
Tools
Anything with a fine firm point: a needle tool, a loop tool for wider lines, a wooden skewer for a softer edge, a metal kidney for scraping back an area. Different tools give visibly different lines, and most people who do a lot of it settle on two or three. Nothing here needs buying specially.
Finishing it
Brush the crumbs away with a soft brush rather than blowing them, because the crumbs are dried slip and blowing them is a dust point in an otherwise clean technique. A transparent glaze over the top seals the work and deepens the contrast, and for functional ware it is what makes the surface washable.
Questions people ask about sgraffito
What is sgraffito?
Scratching a design through a layer of contrasting slip so the clay body shows through, drawing a line by removal.
When do I scratch the design?
When the slip has lost its shine and the pot is still leather hard. Too wet smears and too dry chips.
Do I need to glaze over it?
For functional ware, yes. A transparent glaze seals it and deepens the contrast between slip and body.