Gilding can be described as the covering of a base or common material with a layer of gold. This layer is achieved through the application of gold leaf to an adhesive which has been applied to the surface to be gilded. It must be noted that there are other, lesser materials used to achieve a gilt surface. Composition leaf which is composed of copper and tin can be used. Just as well, bronze and mica powders mixed in a binder can make a ‘gold’ paint. These surfaces, while capable of being very attractive will never achieve the look of true gold leaf. They will also tarnish and discolor with age, never developing a patina.
Gilding restoration is more than re-touching areas of loss with “gold” paint. Experts at Bernacki & Associates first determine type of gilding; water-based gilding dictates different approaches than oil-based. Gilded surfaces are also apt to accumulating residue over the course of time. Removing grime from gilded surfaces without causing further damage is challenging. That involves detailed analysis of gilding type, detergent compounds, and the components within the residue, itself. When gilded surfaces require cleaning, our conservators repeat a slow, careful process. Each small area of gilding is treated over and over again, safely eliminating dust, dirt, and other impurities.
There are two primary techniques used in gold leafing, oil gilding and water gilding.
Oil gilding can provide a beautiful surface coating of matte gold. The process is quicker and less labor intensive than water gilding. In many situations it is as durable as water gilding and uses the same gold. Oil gilding must be applied to a completely sealed surface. First an oil size is applied to the surface. Sizes are now made of many different materials but most commonly are a boiled linseed oil. The applied oil is allowed to dry (oxidize) in a dust free environment until the proper tackiness is achieved. Then the gold leaf is applied.
A basic definition of water gilding would be a porous substrate (typically wood), covered with gesso (usually a mix of calcium carbonate and animal hide glue), covered with bole (a mixture of clay and animal or fish based glues), and covered with a layer of gold leaf held to the bole by organic animal or fish based glues. This golden surface can then be left matte or burnished to a mirror-like sheen. Water gilding is typically much more labor intensive than oil gilding but is also capable of achieving a more refined surface and sheen. Consequently it has been reserved for more expensive objects which are seen and experienced at more intimate distances.
[Excerpt from The Art of Gilding by Bart Bjorneberg. Click here to read the full article.]