A primitive technique of decorating pottery by adding thick slip to the surface of a pot before firing. The term also refers to the creamy mixture of kaolin clay itself, for pottery ornamented with barbotine, and the technique of applying incrustation of this mixture to a ceramic surface for decorative effect. The slip was not applied evenly, but in order to form a thick incrustation in patches or trails. On certain types of pottery, such as the Nene Valley ware, the barbotine decoration may form a picture or a pattern. Sometimes the result is simply a roughened surface, rather like icing upon a cake. The method was particularly popular in Roman Gaul and Britain.