Foundations for Gilding Part II: Water & Oil Gilding

© Amanda Quinby

Gold leaf and gilding have been around since before the Egyptians built the pyramids but it was during the late Middle Ages in Europe that gilt became the preferred finish for picture frames. While beautiful in its own right, the choice of gold was based as much on pragmatism as on aesthetics. In the dim light of medieval halls its reflective properties helped illuminate paintings. Though visually impressive, the truth is, not that much gold goes into a gilded frame. This is because of the metal’s malleability. One gram of gold can be pounded thin enough to cover a queen sized bed. Leaf is typically sold in booklets of 25 four inch squares. It would take 250,000 of those squares, stacked one on top of the other, to reach one inch. Placed end to end, that amounts to a twelve mile path.

As discussed last month, the first step in water gilding is to coat a clean, raw wood frame with gesso, a combination of melted rabbit skin glue and finely ground chalk. Multiple layers are applied and, unless a textured surface is desired, then sanded to a smooth finish. The gesso fills the wood grain and provides a hard, smooth foundation upon which to apply the bole.

If you look carefully at most antique gilded frames you will notice that they usually have a red or reddish-brown undercoat. This is the bole, a mixture of, again, rabbit skin glue and clay. Traditionally, clays were simply the color of the earth from which they were dug, thus the reddish color. They now come in a variety of colors though red remains the most commonly used. Bole provides both a burnishable surface for the leaf as well as additional color that may compliment the gold and the artwork to be framed.  Like gesso, the bole is painted on in successive layers and allowed to dry then sanded with at least 400 grit sandpaper. Some gilders polish the bole with a horsehair cloth before gilding.

The entire surface to be gilded is usually first painted with yellow bole. The highlights are then given the accent color. Leaf, because it is so thin, is inclined to break over uneven surfaces such as the curves and fissures of a complex molding. The yellow bole, of a similar color to the leaf itself, helps to make these faults, or “holidays”,  less noticeable.

Oil gilding requires neither gesso nor bole but both are often used because of the quality of the surface that can be created with the gesso and because of the quality of the colors found in the bole. As an alternative, I often use powder pigments or aniline dyes to achieve a less costly undercoat for oil gilded surfaces. What is required for oil gilding is a sealed surface. I generally use shellac over gesso or, if I want to retain the wood grain, over raw wood. This is especially effective for woods such as oak which have a texturally, as opposed to visually, prominent grain. The leaf will reveal, and in fact highlight, every nuance of the surface beneath it. It is therefore critical that the texture of the surface you have prior to either oil or water gilding is the surface you want after the leaf has been applied.

The leaf is cut on a suede or velvet covered pad with a gilder’s knife. Because gold leaf is so thin it adheres to anything with the slightest amount of moisture, including human fingers. The gilders tip, which is essentially a thin card set with squirrel hair bristles, is designed specifically for picking up the leaf without breaking it.

Every gilder has a preferred recipe for gilder’s liquor. Plain water will work – thus the term water gilding – but a bit of alcohol helps as a dispersant and some gilders also add a bit of rabbit skin glue to their solution. The purpose of the gilder’s liquor is to reactivate the glue already in the bole, thus giving the leaf something to adhere to. The liquor is applied to only a slightly larger section than will be covered with the leaf. A soft sable hair gilders mop is used to thoroughly wet the area without leaving puddles. The leaf is then picked up with the tip and gently but quickly placed on the molding. If the tip is allowed to linger on the surface even that slight pressure will force the water to seep through the leaf, causing staining or torn leaf. The leaf is gently tamped with dry cotton and the process is repeated with each leaf overlapping the previous one by about an eighth of an inch or less. These lap lines, which show up on a well worn or purposefully distressed frame are one way of identifying a water gilded object.

Once the leaf has been laid the frame is allowed to dry. Summer is general the preferred gilding season because of the humidity. High humidity keeps the gesso and bole soft. This is an important factor in burnishing a frame, the final step in the water gilding process.

The application of leaf is slightly simpler for oil gilding because there is no need to coordinate brushing on the gilder’s liquor, cutting the leaf and placing it before the bole has absorbed the water. Instead, a thin coating of size is applied to the sealed surface. During the middle ages boiled linseed oil was the preferred medium. Today oil based sizes continue to provide the most beautiful finished surface but synthetic acrylic formulas are also available. The size is allowed to dry until it has almost, but not quite, lost its tackiness. A fast tack size may be ready in as little as half an hour, depending on temperature and humidity and the thickness of the application. A slow tack size may take up to twelve hours or more to reach the appropriate tack. The leaf is then applied in a similar manner to water gilding, using the gilders tip. It is then gently brushed to remove the excess gold and then rubbed with a cloth to press the leaf into the still soft size. It is then allowed to fully dry. Again, the type of size used determines how long the frame must set up. Fast tack sizes may be ready overnight while slower sizes may require a week or more to harden.

Oil gilded frames cannot be burnished and the surface created tends to be less lustrous than that possible in a water gilded frame. They are, however, simpler to gild. Also, the less expensive base metal leafs such as Dutch metal and aluminum leaf can only be applied using this method. The oil gilded surface has the added advantage of being a bit more durable than its water gilded counterpart as it is not water soluble.

The purpose of burnishing is to create the soft gloss and luster for which water gilded frames are noted. During the middle ages the teeth of large carnivores – dogs, wolves, etc., – were used in burnishing tools. Today polished agate is the material of choice. After the water gilded frame has dried the agate is rubbed over those areas where a glossy surface is desired. Areas left unburnished will remain matte. Fairly heavy pressure is used to compress the bole and gesso and bring up the polished surface. Other precious metals such as 12 karat gold, silver and platinum can also be used for water gilding.

Once the frame is burnished it can be left as is. It remains, however, water soluble. One swipe with a damp cloth will destroy the gilded finish. A light coat of shellac is often applied to protect the gold. Lower karat leafs, because they generally contain silver, also need a protective coating to prevent tarnishing. Since we no longer view art work by torch light the gold is frequently toned down with glazes or washes to avoid glaring garishness. The artwork and the viewing environment should inform the final finish on a new frame. The original existing finish dictates the process of a conservation project or a repair. And that will be the topic for next month.