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Applying clay bole to pastiglia in preparation for traditional water gilding with 23kt gold leaf directly upon canvas.
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Painters sometimes inquire about suggested methods to incorporate gold leaf within their artwork. One thing I often mention is that if one chooses to use immitation gold leaf, generally referred to as metal leaf, dutch metal, or composition 'gold', it is actually brass, an alloy of copper, zinc, and nickel. Since brass tarnishes, it needs a protective coating to guard against, or at least retard, sulphidation, unless the eventual discolorization is a desired effect.
Silver metal leaf in contrast will not tarnish, at least not appreciably, since it is really aluminum and should not be confused with genuine silver which will darken fairly quickly with age if left unprotected. Shellac, although somewhat hydroscopic, is often used as a protective coating and toning medium in gilding. Spar varnish may also be used but its heavier viscosity may produce an unwanted result.
The use of genuine gold leaf in interiors, 22k and higher, does not pose the tarnishing occurances from sulphidation as brass leaf and therefore does not need to be sealed. It is possible that discoloration will not become sufficiently noticed until a karat less than 18 is used. Still, shellac is often applied over genuine gold leaf as it helps to protect against minor handling and is effective in patination. Genuine gold leaf does have a richer, warmer tonal quality than brass leaf and its resistance to discolorization is one of its many benefits. Its expense, however, needs to be considered by the artist as to whether the additional cost is warranted.
There are numerous methods of gilding and a wide variety of materials used; however, when considering a method that employs the use of an adhesive binder that is applied directly to a surface, it should be noted that gold, silver, brass, or aluminum leaf will adhere to any slightly tacky surface. The lighter the tack the more brilliant the tone and the higher the tack the better the adhesion. A balance therefore needs to be obtained for proper adhesion while maintaining an attractive appearance in the leaf.
Various mediums can be used to adhere the leaf as long as there is compatibility with the medium of your artwork. As an example, leaf could be laid directly to acrylic paint on a canvas after it has set for a while. Clear acrylic medium or glaze may be used as well. For water colors one may wish to use gum arabic as the binder of the leaf to the paper in which two coats may need to be applied, the first as a sealer. It's always a good idea to test your chosen approach on a test piece first. Traditional gilding binders used over the centuries include gum ammoniac, gum arabic, boiled parchment clippings, linseed oil, glair (egg white), hide glue, issinglass, and other various mordants. Their use extends to iconography, the polychromatic works of manuscript illumination, frames, furniture, statuary, architectural embellishment, verre églomisé, among others.
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June 1
