There are two types of gilding used on mirrors: oil gilding using a type of glue based on linseed oil with gold leaf laid on with a gilder’s knife, tip and cushion; or water gilding, a more intricate process which consists of applying a series of coats of gesso, layers of bole ( a refined clay in a variety of colours), on top of which gold leaf is applied, then a protective coat of ormolu. You might wish to see samples of each type before you decide how you would like your mirror to be refinished. Specialists in gilding include the following companies: E & A Wates, Bourlet, Titian Studios.