Conservation in Action: Benjamin West Frame, March 2015

Treatment of the frame for Benjamin West’s Devout Men Taking the Body of Saint Stephen:
March 2015

The cleaning undertaken in the past few months reveals that the frame’s gold leaf surface is covered by a layer of old bronze powder paint. This paint coating likely dates to before the 1940s and would have been applied to brighten up a dull or damaged surface. Today, it has oxidized to an unsightly brown color.

Removing the bronze paint without damaging the underlying gold leaf is a less-than-straightforward task. The first step is to examine samples from the gilded surface. Tiny samples are taken with a sharp scalpel and carefully collected into small vials. The samples are then imbedded within a transparent resin block and polished, before they are viewed through a high-powered microscope. Under magnification, conservators can view the sample in cross section to distinguish the original gold from later applications of gilding and paint layers. Below is a magnified sample viewed in cross section and illuminated with ultraviolet light.

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To better understand the history of the frame’s decoration scheme and its past restorations, a varied selection of samples is taken and compared. The location from where each sample originates is carefully chosen and tracked on a corresponding map. Samples are taken from all four sides of the frame (below left), and as can be seen in the profile view (below right), from all the different pieces of the wood molding.

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The image below shows damaged gilding where a sample was taken. When such samples are viewed under magnification, their cross sections can reveal the many layers associated with gilding. Typically, the first layer on top of the wood is a sealing layer of glue. It is followed by gesso, a mixture of glue and chalk, which creates a rock-hard base. A thin layer of colored clay and glue, known as bole, or a layer of varnish is applied on top of the gesso. This is followed by gold leaf, extremely thin sheets of gold just microns thick, applied either onto the bole or the varnish layer depending on the technique employed. There are two primary techniques: water gilding and oil gilding. The names refer to how the gold leaf is adhered to the surface. In water gilding, the bole is dampened, which reactivates the glue. In oil gilding, an oil size is applied on top of the paint layer and the gold leaf is added at just the right moment in the drying process. Finally, above the gold leaf, there is often a sealing layer of diluted glue or varnish.

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Over time the different parts of the gilding age. Wood tends to shrink as it loses water content, but the layers on top do not. While wood keeps its ability to absorb and expel moisture from the surrounding air, the layers on top do not, and the constant micro-movement of the wood causes the binders of the gilding layers to lose their elasticity. This leads to cracking, lifting, and flaking of the gesso. The vertical cracks seen in the cross section below are a result of such wood movement. More layers mean a more complex task for the gilding conservators, and on this frame, there are an estimated eight layers to consider.

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Study of the samples confirms what conservators suspected—that the frame had been gilded twice, and overpainted once. Below, the two gold layers can be seen as two glittering hairlines, so thin that only their reflection is visible even under x200 magnification.

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The samples also help establish that both oil and water gilding were employed for the original decoration of the frame, with matte and burnished areas skillfully combined in the classic Carlo Maratta style. As outlined in the following diagrams, there are four passages of water gilding on the original surface, with remaining areas using oil gilding. In the second layer of gilding, applied during the frame’s first restoration, there are only two water-gilded surfaces and the remainder is covered with matte oil gilding. The samples do not explain the reason, but perhaps it was a less skilled or more quickly executed job than the original. Water gilding takes more time and skill, and thus also tends to be more costly.

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See next update.