In bookbinding, a means of decorating a book by using a heated metal, usually brass, instrument to adhere gold leaf onto the cover of a book. Glaire, the generic name for the adhesive to be used is applied to the area to be gilded. Glaire may be either spirit-based or a water based, protein suspension, commonly egg white suspension in water.
The heat from the heated tool 'cooks' the glaire, causing it to stick the gold leaf to the leather paper or cloth, or even to a vellum cover.