Gilding is the name given to the process of laying gold leaf onto furniture or frames. The technique and the tools used have changed little since the 18th century.
There are two forms of gilding commonly used – oil gilding and water gilding – oil or water referring to the medium in which the gold leaf is laid.
Water or burnished gilding requires the surface of a piece of wooden furniture or frame to undergo many different processes, prior to the application of gold leaf. Water gilding is always laid onto a prepared surface of gesso (a mixture of water, glue and whiting). Once gesso has been applied and dried it forms a surface which can be smoothed to an extremely fine finish creating an ideal medium on which to lay gold leaf.
On finely carved objects gesso is applied very thinly, so that the detail of the ornamentation is not obscured. In the 18th century, however, many items were carved roughly in the wood, and had a thick application of gesso which was then completely re-carved with fluted and veined decoration to give fine definition.
The gesso surface is carved, smoothed and then sealed with a coat of glue size and yellow ochre clay.
Coloured bole is then applied over the yellow ochre to all the top surfaces of the object. Bole is a form of coloured clay with excellent burnishing properties. This accentuates the richness of the gold leaf.
Gold leaf is available in a variety of colours and carats. The carat indicates the purity of the gold and its colour is altered by the addition of other metals. A book of gold consists of 25 leaves that have been beaten wafer thin. Each leaf of gold is approximately 80mm x 80mm. Gold leaf is applied directly on to the coloured bole. To lay the gold it is taken from a book and placed on a gilding cushion (a leather pad semi-surrounded with a raised border to prevent the gold leaf from blowing away). The leaf is cut into manageable segments and picked up with a squirrel hair gilding tip.
A small area of the bole surface is brushed with water and the segment of gold leaf is carefully laid onto the wet surface. Another piece of gold is cut and the process repeated. This is carried out over the whole surface being gilded, and is then left to dry.
Using an agate stone, the gilding is burnished to a brilliant shine, a characteristic of water gilding.
To achieve a richer and more perfect finish, some items may be double-gilded. This requires a second layer of gold leaf being laid directly on top of the first layer, after which it is re-burnished.
The oil gilding process is far simpler than water gilding. There is less preparation and it is easier and faster to lay the gold leaf.
Although the surface to be gilded can be prepared with gesso to obtain better results, it is quite sufficient to merely seal the surface with a coat of paint or polish. An oil size is painted onto the prepared surface and left to dry. When the size is almost dry, the gold leaf can be taken straight from a book and laid directly onto the slightly tacky surface. The gold will stick wherever the oil size has been painted.
The disadvantage of this technique is that, unlike water gilding, the gold cannot be burnished and the same subtleties of finish in the ageing process cannot be achieved.
Oil and Water Gilding
In the 19th century it was common practice to gild objects in a mixture of oil and water gilding. The more intricately carved areas were often laid in oil, which saved time, whilst the larger areas such as scrolls and hollows were water gilded and burnished achieving a contrast in both colour and shine.