Tooling is the decoration of a surface with the aid of metal hand tools and stamps (a technique employing the latter being termed stamped). On bindings, the tools were used to impress the decoration into the leather covering, which was often dampened. The impression or indentation produced is called blind if it remains uncoloured. Gold tooling became popular in the fifteenth century. In this process, gold leaf was laid onto a coating of glair and impressed into the leather with a heated tool, leaving an image in gold after the excess was rubbed away. Gilded surfaces (see gilding) in illumination were also sometimes tooled.