GILDING….notes on

November 4, 2014 in Frames by Tim Everett

Gold Leaf

Gilding is the process of applying a thin layer of gold leaf onto a prepared surface of gesso, which is a paste base.  The gilt surface can be burnished to create a bright finish.  There are different types of gilding, including oil gilding, water gilding, and mercury gilding.

 

Interior of a Frame Gilding Workshop (oil on canvas), Adan, Louis Emile (1839-1937) / Musee des Beaux-Arts, Angers, France / Giraudon / The Bridgeman Art Library

 

Gilding Techniques:
Two main techniques are used when applying gilding to architectural decoration: - oil gilding and water gilding.

Oil Gilding:
This method can be used to apply gilding to most internal and external building surfaces.  The first step is to prepare the surface onto which the gilding is to be applied. This is done with paint or gesso. Gesso is made by mixing chalk or gypsum with liquid glue known as size. This is covered in a thin layer of gold size which is left until it is nearly dry and ready to accept the gold leaf. Finally, a protective coating can be added.

Water Gilding:
This process requires greater preparation of the surface onto which the gilding is to be applied but, compared to oil gilding, a superior finish can be produced. Before water gilding is applied a number of coats of gesso need to be built up on the substrate to produce a smooth surface. This is followed by several coats of bole. Bole is coloured clay mixed with size. The surface is then wetted with a mixture of water and metholated spirits and the gold leaf applied instantly. As the
water soaks into the gesso it draws the gold firmly onto the surface. The gilded layers are then polished using agate (a form of hard quartz like stone) burnishers. Judging when the surface can be burnished is critical. If the correct degree of dryness has not been achieved the leaf can be easily damaged. The burnished gilded layers can, if required, be toned down using oil based varnishes and pigments.

 

Materials used in gilding:
Despite variations in technique of application, the same basic materials of leaf and size are integral to all methods. As with all elements of traditional buildings, an understanding of the materials used is conducive to their proper care. With gilding the following should be noted:

l Leaf: Very thin sheets of metal (around
1/250,000th of an inch thick) are used
and are supplied on a backing paper in
“books”. The most common type of leaf is
gold although other metals, such as silver
or platinum, can be used. Gold can also be
alloyed with other metals to provide different
tints and shades. In common with all gold,
leaf can come in varying degrees of purity
ranging from 12-24 carats. The purity of the
leaf can alter the appearance of the finished
gilding.
l Size: In oil gilding a liquid glue known
as gold size is applied to the substrate. This
forms an adhesive that acts as the binder
between the metal leaf and the prepared
surface. This size is most commonly made of
heated linseed oil although, in the past, other
materials such as rabbit skin glue were used.
In water gilding size is mixed with water to
help provide the necessary composition to aid
adhesion between leaf and substrate.
l Gesso: In order to provide the surface to
receive the gold leaf a fine plaster-like material
has to be applied to the substrate. This layer of
gesso is made by mixing chalk or gypsum with
size. Warm liquid gesso is applied in several
layers and, when dry, is sanded to a smooth
finish to create the necessary surface.
l Bole: Bole is applied over the gesso layer.
In water gilding techniques bole is used
beneath the leaf to create a very fine, hard

surface. This allows the gold to be polished
(burnished) to a bright sheen. In some cases
the colour of the bole can influence the
appearance of the finished work.
l Surface coating: After gilding has been
applied it is sometimes coated for aesthetic
reasons or protection. Silver gilding is always
coated with varnish to prevent it becoming
tarnished. The surface coating can take
the form of lacquer, clear glaze, or toned
varnish, depending upon the desired level of
protection or required appearance. It should
be maintained thereafter because removing it
exposes the leaf and alters the appearance.
l Tools: A variety of specialist tools are used
in the gilding process. A gilder’s pad and knife
are required to cut the leaf into the desired
size and shape for the job. A flat brush is used
to transfer the leaf from the pad onto the
substrate, and these come in a variety of sizes.
Other brushes are used to smooth the gilding
into position, and to remove excess leaf. A
variety of other tools are employed in the
application and preparation of gesso, bole and
finishing.