A stamp presses a mark or a texture into soft clay, and it does two jobs: it signs work, and it decorates it. Both are worth doing, and a maker's stamp in particular is the difference between a pot that is identifiably yours and one that is anonymous.
Maker's marks
A personal stamp pressed into the foot or the side while the clay is soft identifies your work permanently, survives the firing and takes a second. Commercial services make them from a design, and a great many potters make their own by carving a plaster or bisque block. Either way it is the single most useful stamp to own.
Texture stamps
Stamps that press pattern into a surface, used singly as a motif or repeated as a border. Commercial ones are sold in sets; found objects work as well, and anything with a firm surface and a pattern can be tried. Wooden printing blocks, shells and machined parts all give crisp repeatable texture.
Making your own
Carve a design into a small block of soft clay, bisque fire it, and you have a permanent stamp. Carving into plaster is quicker and gives a stamp that absorbs moisture and releases cleanly. Both routes cost nothing beyond materials already in the studio and produce something no supplier sells.
Using them well
Stamp soft, not leather hard, and support the wall from behind so the pressure does not distort the pot. A dusting of cornflour or a wipe of oil on the stamp helps it release from sticky clay. Test the depth on a scrap first: a mark that reads well on soft clay can almost vanish under a thick glaze.
Questions people ask about pottery stamps
When do I use a pottery stamp?
While the clay is soft, supporting the wall from behind so the pot does not distort.
Can I make my own stamp?
Yes. Carve soft clay and bisque fire it, or carve plaster, which releases cleanly because it absorbs moisture.
Why did my stamp disappear after glazing?
A thick glaze fills a shallow mark. Stamp deeper, or use a thinner glaze where the mark matters.