Scientific American 4, 22.7.1868
A correspondent inquires why picture and mirror frames which are gilded receive a coat of some white composition before being gilded, while the letters and ornamentations on signs, mahde also of wood, do not.
It will be noticed that picture frames when gilded have a luster - are burnished - while the letters on signs are "dead". The composition referred to is necessary to this burnishing, as the wood would "give" too much and the leaf be broken and destroyed. To prepare the frame for the gold leaf a mixture of hot size and whiting, quite thin, is applied evenly, and followed by successive coats, each thicker than the other, care being taken that the ornaments or carvings are not clogged and filled by the mixture. The coating when completed is about one-sixteenth of an inch thick, and is smoothed with pumice stone. Upon this bed is laid a composition of clay, red chalk, plumbago, suet, and bullock's blood. The leaf is then applied precisely as in ordinary gilding, which will be presently described, and burnished with agate or bloodstone set in convenlent handles.
In ordinary gilding, as for the lettering on signs, no preparation is necessary, except to apply a mixture of boiled linseed oil and ochre, called gold size, which should stand over night or for a few hours until, to the practiced touch, it is of the proper viscidity to receive the leaf. The application of the leaf appears to be perfectly simple, but it requires much experience, dexterity, and the exercise of discretion and good judgement. The gold leaf comes in "books", each leaf of which is coated with red chalk, an argillaceous oxide of iron, to prevent the adhesion of the gold to the paper. The gilder, holding in his left hand a cushion covered with soft leather and in his right and the foot of a rabbit or hare, removes one of the gold leaves from the book by simply touching it with the hare's foot or lifring it with a thin steel blade, and conveys it to the cushion, on which he spreads it by gently blowing upon it, by which he smoothes out all the wrinkles. With his blunt edged knife, similar to a painter's palette knife, he cuts the leaf into pieces adapted in size to the spot to be guilded, and with the hare's foot lifts the piece and dexterously conveys it to its place, finishing the process by touching the uneven portions with a soft came's hair pencil. No draft of air can be allowed in the room where this work is done, as the particles of gold leaf are so light that they fly at the slightest breath. Sometimes it is necessary to press portions of the leaf into depressions of the work, if for instance it is a carved frame, by a wad of soft cotton, but this cannot be used in a damp atmosphere.