Applied to any opal the miners consider valueless, even though it may exhibit some color flashes. Sometimes opal with a few color flashes is called potch with color. There are many varieties of potch; jelly (clear and glass-like), white, milky, grey, blue, honey, black potch and chalky potch (soft, crumbly, white opaline silica). Geological definition - lustrous opaline silica with no play of colors.