Elmers glue as a resist. Unlike wax, it is (1) water-soluble, and therefore can be washed off a bare pot if you make a mistake, and (2) removable, like latex, although it does take longer to dry than latex.
Bowl, stone-paste painted with glaze.: Iran, 12th century. Photograph and description taken from Freer and the Sackler (Smithsonian) Museums.
Matthew Hyleck | Stoneware field plate.
Handbuilding Pottery Projects Ideas & Pictures...tons of pictures!