Lately we have been working with the magic of chemistry to bring back the luster of some archival materials. The specific “trick” is reverting blackened lead white pigment back into its intended colorless form. The object I am referring to is a scrapbook of handkerchief patterns with stripes and geometrics painted in opaque gouache (thick watercolor). The scrapbook, a “National flat back with black skiver cloth back and corners and black paper sides,” consisted of 100 leaves. It is part of the Thomas Lamb papers and the painted samples were made in the mid 1920s. Many of the pages show an insane number of handkerchief pattern options involving varieties of width and spacing of white ruled lines, while others offer creative colorblock combinations, or slightly kooky patterns.
The scrapbook before treatment. The left page has samples painted in lead white gouache.
It’s not uncommon to find many problems with scrapbooks in archives and this item had it all: brittle pages, painted samples falling off or laying loose in the gutter, discoloration from acids in the paper, and areas of white paint and colors that had become gray and muddied. Since our primary goal is to preserve our collections, but make them usable by researchers, we had to stabilize the scrapbook prior to any aesthetic treatment of the paints. It was painstakingly disassembled and the painted design samples were re-adhered to new sheets of lignin-free and acid-free paperboard by our intern Megan Murphy. The new paper will not outgas acids or other degradation products over time, as the scrapbook pages had.
Now each page is stored in a polyester sleeve, and we can proceed to the improvement of the discolored pigments. Lead White was the primary white pigment used for painting until around 1921, when it was displaced by titanium white and zinc white. It consists of about 70% lead carbonate and 30% lead hydroxide. For many hundreds of years the best method of generating the pigment was to expose metallic lead to vinegar. Over the course of its history it was referred to by a myriad of other names including: flake white; Flemish white; Vienna white; and Dutch white lead. Under ultraviolet light it gives off a reddish purple fluorescence.
There are a couple of problems with lead white. The first is its toxicity. It is now widely banned in interior paints and its remediation in homes is an ongoing problem. The other problem it has relates to preservation. Lead white is sensitive to sulfur compounds (think exhaust and industrial pollutants) and alkalies (materials over pH of 7). When exposed to these compounds, the lead white pigment turns an unsightly range of hues, from yellow, to brownish, to all shades of gray and even black.
This image of the discolored lead white was photographed through the microscope.
You might imagine how disturbing it can be to the look of a work of art, when the white was used as a highlight in an illustration now looks black! Fortunately, the careful and controlled use of hydrogen peroxide in a gel, balanced to the proper pH, is able to convert the discolored lead white back to a white form.
Hydrogen peroxide gel was applied to this paint in order to revert the pigment back to white.
Laura Wahl is the Library Conservator at Hagley.