Peeling Back Time

A home owner who wishes to restore a house's original paint colors—or who is simply curious about them—may want to consult an expert from a conservation firm. A tiny sample or plug from a wall is removed, cast in resin, and polished perpendicular to the layers. An examination under high magnification and ultraviolet light will help distinguish between even "a million shades of white," says Brian Powell of Building Conservation Associates in Boston, Massachusetts. "Different layers will reveal different amounts of fluorescence," corresponding to materials used during various periods. Because colors tend to fade over time, paint conservators look for drips and other thick areas that have a more protected core. Lacking a pristine sample, says Powell, "you have to use a curatorial eye and correct based on what you know of a paint's properties." Verdigris green—an expensive shade used on interiors in the 18th century—eventually turns a dull brown; prussian blue fades easily; and linseed oil, a common paint ingredient, darkens and yellows away from light, so that it could throw off a sample taken from behind a shutter. Once the right color is identified, the experts fingerprint it by measuring it on a chromometer. Then they match it to a paint chip from a modern-day manufacturer.

Home owners can use a cruder technique called cratering. Slice a small patch of paint away from the wood, then lightly sand around it. Layers of color will feather away from the center and gradually reveal the earliest coats.
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