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Frames & Gilded Objects  Conservation

Not infrequently, frames and other gilded objects are improperly restored with bronze paints, often applied to mask surface abrasions and losses. The paint may have looked acceptable upon application, but over time the metal powders in the paint oxidize and turn dark. Fortunately, bronze paints applied to water gilded surfaces are often easily removed with appropriate solvents. Bronze paint applied over oil gilding is often difficult to remove and in many cases impossible because of the similar solubility of the paint and oil binder.

Frame and gilding preservation treatments often combine elements of conservation and restoration. The combination of materials such as gold and other metal leaf, bole and gesso are inherently delicate and therefore susceptible to various environmental factors. Uneven relative humidity and temperature can affect wood substrates and lead to expansion and contraction. The result is often cracked and flaking gesso, bole and metal leaf layers.

Beautiful gilded frames and furniture, with their brilliant reflective surfaces are a result of careful preparation before the gold leaf is applied. Gesso, a mixture of calcium carbonate and rabbit skin glue, is applied warm to the surface to be gilded. Gesso is also frequently the ground layer applied before other decorative surface treatments such as paint or japanning. Gesso fills irregularities and other imperfections in the surface of the wood resulting from carving, planing, various tooling marks and occasionally inferior coarse wood texture. Usually several coats of gesso are applied and allowed to dry before the gesso surfaces are worked to create detailing or to smooth the surface in preparation for the bole coating. For example, sculptural details in carving are sometimes worked in the gesso coat rather than the wood substrate. 

Bole is a mixture of clay and rabbit skin glue. Available in several colors the bole layer can impart subtle tonal qualities to the gold.  Sometimes two or more bole colors are applied, with each fulfilling a very specific purpose. It is not unusual to note yellow and red bole applied to a frame or other object. Yellow will often be applied to recesses within and adjacent to carving; red to the elements of the carving that stand proud of the surface. Because it is nearly impossible to apply gold to every crevice and recess, the yellow bole is used in these areas to create the illusion of a completely uniform appearance.

Gilded surfaces require very little maintenance other than careful dusting. Longevity is best achieved by maintaining stable environmental conditions. Because of the fragile nature of gilded objects, ongoing inspections are important. Should flaking or curling or other defects in the gilded surfaces be noticed, they should be addressed immediately. Always save any surface elements that become detached.  Immediately addressing minor condition defects will greatly reduce the cost of what otherwise can be a very time consuming and expensive treatment.

Prior to the nineteenth century nearly all gilded substrates were comprised of wood.  Panels, mouldings and carvings were all prepared by craftsmen before the application of gesso. By the late eighteenth century; however, the use of composition ornament, fabricated by specialists and sold to other craftsmen, permitted extensive embellishment without the cost of carving in wood. The process involves the fabrication of a reverse carved element, the mold, in a block of densely grained wood. Composition, or the casting material, was typically comprised of glue, resins and various bulking agents.  It was pressed into the mold and removed after hardening. Ornamental castings were (and still are) made in a variety of forms and sizes which could then be used to enhance frame mouldings or architectural elements such as chimney surrounds.

Further details in breast and wings of bird are carved in the gesso layer. The restoration beak is carved pine with a gesso coating.

After drying, the bole is burnished; usually with horsehair cloth. This is a critical step if the objective is to create a continuous reflective surface. Gold cannot be burnished properly if there are irregularities in the bole coating.  Gold is usually applied in one of two ways with either an oil size or a water/glue binder.  It is not unusual to employ both methods on the same object to create varying visual effects. Typically, flat areas, continuous mouldings and sometimes discreet sections of carving will be water gilded.  Whereas, recesses and most carved elements are usually oil-gilded. Water gilding can be burnished to a high gloss; however oil gilding is not burnished. A well prepared and burnished water gilded surface glows like a block of bullion. Another telltale mark of water gilding is the perfectly spaced lap lines visible on a flat surface or continuous moulding. The subtle effects that are possible combining water and oil gilding are often an important part of the overall aesthetic effect.

Frames with varying colors of gold and bole.

Treatment Examples (click on each of the images for more information):