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Preservation

Inside the Conservation Lab: Treatment of an Engraving on Silk

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Print on silk adhered to cardboard mount.
Calvary - Before Treatment

As the New York Public Library's Paper Conservator, most of the objects that I treat are flat paper items, such as documents, maps, and prints. Recently, I worked on some projects from the Prints Division that were more unusual; like this engraving on silk that came to conservation to be removed from its old mount and get better, updated housing.

Calvary is a crucifixion scene printed in black ink from a dome-shaped plate onto fabric. It was originally aquired from a London dealer who noted: "This print by an amateur engraver is dedicated to Kaspar Kindelman, Abbot of Ottobeuren from 1547-1584… This is a beautiful example of the work of a late sixteenth-century amateur with knowledge of early Italian Renaissance prints."

The platemark (or plate impression) is visible about 6mm beyond the engraved border. Under the microscope, two distinct layers of the fabric could be distinguished. The bottom layer is constructed of bundles of white fibers lying side-by-side horizontally. Finer, vertical strands of pale gray, shiny fibers rest on top of, and interweave with, the bottom layer. The right and left edges appear to be selvage edges, where the horizontal fibers fold back inward on themselves and are tightly woven in with the top layer. At the top and bottom, where the fabric appears to have been cut from a larger piece, the fibers are loosely bound. Six stray fibers were resting on the backing board near the top and bottom edges, but no longer attached to the object. I placed these on a microscope slide with a drop of deionized water, examined them under a polarized light microscope, and compared them to known sample slides. Four of the fibers were close matches with the silk sample, and two of the fibers were close matches with the cotton sample. I surmised that the thicker, bottom layer of the fabric is cotton, while the finer, top layer is silk.

The engraving is dated 1570, but this impression may have been made after that date. The object's file notes that it was examined by Clare Browne of the Victoria and Albert Museum, who "confirms that the silk dates from the seventeenth century, and was made certainly before the industrialisation of silk production in the eighteenth century."

The textile had been mounted to a thick backing board using a yellowish adhesive, which was tested using chemical tests for both protein and starch[i]. The protein test was positive, while the starch test was negative, suggesting that the adhesive was derived from animal collagen.

The main difficulty with this treatment stems from the fact that the adhesive was water-soluble, while silk is very sensitive to water. To minimize exposure to moisture, I first removed the cardboard backing layer-by-layer. After many hours, all but the board fibers embedded in the adhesive were removed. The adhesive was scraped with a variety of small tools until no more could be removed using dry methods.

Verso of silk print after adhesive has been removed
Calvary - After Treatment Recto

I tested various methods of removing the adhesive while keeping the silk as dry as possible. The most successful was to place a tiny square of damp blotter on the adhesive, then briefly press a small heat tool on the back of the blotter. It would create a faint hiss as the dampness was pulled toward the heat and the adhesive transferred onto the blotter.

This photograph shows the back of the print after the adhesive was removed. Instead of using adhesive to attach the print to a new mount, it was sewn to a larger piece of lightweight polyester fabric with silk thread. The polyester was stretched around a piece of matboard and covered with a new mat. It was not necessary to apply any new adhesive to the print this time around, and it can be easily removed from its mount in the future.

Silk print after stitching to polyester
Calvary - After Treatment
 

[i] Odegaard, Carroll and Zimmt. Materials Characterization Tests for Art and Archaeology, ed. 1. Archetype Publications, London: 2000. Starch test: page 128; Protein test: page 144.

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