The Ancient Art of Gilding

by R. Wayne Reynolds

When visiting a museum we look with delight at paintings produced by generations of artists. But sometimes we miss rare and beautiful works of art that hide in plain sight — the antique gilded frames that surround many of those paintings. These are often extremely complex in design and construction, and required a tremendous amount of time and skill to create. The best of them have such perfect design and workmanship that they add immeasurably to the enjoyment of the art they surround and protect.

Today, these antique gilded frames are highly valued and are often collected as decorative art objects, completely independent of their intended function as a frame. If you have a gilded frame, you owe it to yourself to know more about it: how it was made and why, how to evaluate its condition, and what options there are for treatment and restoration of frames that may have deteriorated or become damaged.

The Gilding Process—How It’s Done
The application of extremely thin sheets of genuine gold to a prepared surface is a skill that dates back over five hundred years. It has remained popular to this day, after all it seems to create a solid gold object from the most basic of elements: wood, rabbit skin glue, chalk, clay, water, and, of course, a little bit of real gold.

Here’s how it’s done. First you need very thin sheets of gold leaf (today they are approximately 1/250,000 of an inch thick). Take a carved wood object and brush on multiple layers of gesso, a heated mixture of glue, whiting (chalk) and water. When the gesso cools and dries, it forms a hard “shell” that covers the grain of the wood. Then rework the gesso layer to remove all evidence of brush strokes and surface texture.

Next, add 3-4 coats of bole, a very fine particle clay combined with rabbit skin glue and water. When the bole is dry, the gilding can begin. Wet the object with gilder’s liquor, a solution of water, alcohol and a little rabbit skin glue. While the surface is still wet, cut a piece of gold leaf with a gilder’s knife, lift it with a squirrel hair brush called a gilder’s tip, and then carefully lay the sheet of gold down on the bole. The gilder’s liquor will activate the rabbit skin glue in the bole and as the water evaporates, the gold is slowly “glued” to the object.

Because the bole provides a cushion between the gold leaf and the gesso, you can then burnish the gold to a mirror-like shine with a specially-shaped agate stone. Often this technique is used on ornaments and moldings to create a distinct contrast with areas that are left matte or un-burnished. This creates a delightful play of light on the surface of the gold.

Evaluating the Condition of a Gilded Object
Like all works of art, gilded frames are constantly subject to damage and deterioration. The first step in caring for them is to evaluate their condition. This involves examining their structure, gesso layer, ornamentation, bole layer, surface finish layer, and even the collected dirt, smoke residue, and tarnish that make up the object’s “patina.”

THE STRUCTURE. With picture frames, something as simple as a loose miter joint can be dangerous to the integrity of the whole object. On gilded furniture, the small wormholes commonly thought to be a sign of authenticity and age, are actually caused by powder post beetles and can cause very serious weakness in weight bearing arms or legs.

THE GESSO LAYER. The gesso on a frame can last for hundreds of years. But if it is exposed to excessive alternating damp and dry conditions, the resulting stress will cause it to flake off its wood substrate. Like an open wound, a compromised surface can be the first step to deeper and more serious damage. Flaking gesso is a warning sign that treatment is needed immediately!

ORNAMENTATION. A missing ornament on a picture frame is a serious visual distraction, and relatively easy to replace. This was not always the case. For hundreds of years, frames were carved in wood, a versatile medium well suited to gilding. But carving wood was time-consuming and, worse yet, it wood was prone to splitting and breaking along the grain.

At the turn of the 19th century, the invention of a radical new material called “composition” changed frame making forever. Composition, or “compo” for short, is made from rabbit skin glue, whiting, linseed oil and rosin. This forms a heavy paste that can be pressed into molds to create ornaments. For the first time, this allowed frames to be manufactured in quantity and with a speed that far exceeded the earlier hand-carving process. Mass production, in turn, gave rise to an unprecedented number of designs and patterns. However, the new material had problems of its own. A common problem is that the linseed oil and rosin in compo can shrink and crack, causing ornament to separate from base frame molding.

FINISH. This is, perhaps, the most complex part of any evaluation. There are many different possible finishes, and they can be applied with different techniques. Correctly identifying these is essential before an object is repaired or even cleaned. Without this information, even the wrong cleaning approach could leave you wiping the gold right off your object!

Gold leaf comes in different grades (purities), with pure gold being 24 karats. Most of the gold leaf used for gilding is 23 karat or less, meaning that the gold is mixed with small amounts of copper and silver to produce subtle differences in color.

What is called “white gold” contains a generous helping of silver, giving it a “warm” silvery tone. There is also pure silver leaf and several types of what is know as “imitation,” or “metal leaf.” It is important to determine which of these was used on your gilded object because they each have distinct properties.

The easiest finish to apply is bronze powder. It can be mixed with a wide range of binders, and painted on. It is inexpensive, readily available, and requires very little skill to apply it. Unfortunately this falls into the “too good to be true” category. As a professional gold leaf conservator, I spend way too much time removing old tarnished “touch ups” or complete “repaints” done with bronze powder paint. If the surface of your frame is a uniform dull, brownish gold, chances are it’s not dirt from old age, but tarnished bronze powder paint from an earlier attempt to restore the finish.

THE BOLE LAYER. The bole layer sits just below the gold leaf, and is usually red or grey. You will see it revealed in the high points of contact on antique gilded objects where the gold leaf is worn off. It will often influence the overall color tone of the object. This is true especially as the gold leaf wears away, revealing more of the bole layer. The color of the bole layer can even contribute to our knowledge of the history of an object, since certain colors were preferred in particular countries during different historical periods.

THE PATINA. Not all, but the majority of gilded objects were originally bright gold in color. But over time they develop what is called a “patina” — a beautiful mellow glow caused by a combination of oils, soot, tobacco smoke, and other atmospheric contaminates. Although real gold does not ever tarnish, abrasive cleaning and dusting of gilded objects over time can grind these elements into the surface and tone down the bright gold finish.

APPLICATION TECHNIQUES. The two most common application techniques are “water gilding” and “oil gilding.” The older, and more difficult technique is water gilding, where the adhesive coating is water-based. With the invention of oil painting, gilders developed an oil-based process for their art as well.

Identifying which process was used is essential. Water gilding must be cleaned with mild solvents like mineral spirits or denatured alcohol, while oil gilding can be cleaned with a mild water based soap solution. Using the wrong cleaner can have disastrous consequences.

The Conservation of a Gilded Object
Like any work of fine art in need of care, antique gilded objects require specialized knowledge from a trained professional. Without that experience it is far too easy to do more damage than good when working with gold leaf.

While each case is unique, there is a basic process we follow when treating gilded objects:

  • Repair structural weakness
  • Stabilize flaking gesso with hot rabbit skin glue
  • Replace missing gesso
  • Re-carve missing ornaments or cast them from a mold made with dental impression material
  • Duplicate the bole color as needed
  • Apply new gold leaf as needed (a process called in-gilding)
  • Blending the new gold into the old gold to soften the transitions
  • Custom mix a thin glaze from a variety of earth colors and carefully apply it to make the new leaf match the original patina

The result is a restoration that is as close to invisible as we can make it.

As the owner of a gilded object it is your responsibility to decide how far treatment should go. “Minimum treatment” will be non-invasive, “medium treatment” will involve a blend of carefully-considered conservation techniques, and “complete restoration” will return the object to its original intended form—a beautiful, shining, golden work of art.
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R. Wayne Reynolds is the owner of Giltwood Restoration in Germantown, New York. You can visit the Giltwood Restoration Art-Care web page by clicking here.