A pot still is a type of distillation apparatus or still used to distill flavored liquors such as whisky or cognac, but not rectified spirit because they are bad at separating congeners. Pot stills operate on a batch distillation basis (as opposed to a Coffey or column stills which operate on a continuous basis). Traditionally constructed from copper, pot stills are made in a range of shapes and sizes depending on quantity and style of spirit. Geographic variations in still design exist, with certain stills gaining popularity in regions of appalachia.