4 MATERIALS

4.1 FABRICS FROM THE FIRST LADIES COLLECTION

Fabric samples were taken from several of the gowns that had been on exhibit in the First Ladies Hall when it was closed for renovation in 1987 (see table 2). Whenever possible, examples of silk fabric were taken from inconspicuous places (e.g., accessible unfinished inside seam allowances). As samples were taken from unexposed areas of the garment, they were likely to be in better condition than the fabric in exposed areas. These samples were, however, considered typical of both the silk fabrics from their respective eras and of textiles in many museum collections. Sample sizes varied, but all were approximately thumbnail size with weights varying from 1.0 mg to 1.3 g. Prior to this study, the gowns from the First Ladies Hall had been vacuumed as part of ongoing conservation treatment. The fabric samples taken directly from the gowns in the Ceremonial Court Exhibition case (those of Jacqueline Kennedy and Patricia Nixon) had not been vacuumed prior to sampling. Samples of the fabrics used in Barbara Bush's inaugural gown were donated to the collection by the designer.

TABLE 2 FIRST LADIES GOWNS SAMPLED

4.2 ARTIFICIALLY AGED SILK HABUTAE

A plain woven silk habutae (Testfabrics style #609) was used for comparison to the naturally aged fabrics in the First Ladies Collection. The use of commercial degumming, causing removal of the sericin, was confirmed by amino acid analysis of the material extracted (0.5% of fabric weight) after boiling the habutae in deionized water for 30 minutes (table 1). The hot water extract had an amino acid composition similar to the amorphous region of silk fibroin, not sericin, confirming that the fabric was completely degummed (Becker 1993).

The new silk fabric was artificially aged by exposure to a xenon arc light source in an Atlas Ci-65 Weather-ometer (Atlas Electric Devices 1986). Fabric samples were mounted in sample holders with four exposed areas of 42 � 50 mm per holder and irradiated for varying lengths of time up to a total dose of 1000 kJ/m2(Becker and Tuross 1994). Three sets of artificially aged habutae were prepared by exposures using three different combinations of glass filters—borosilicate-soda lime, borosilicate-borosilicate, and quartz-quartz—with lower wavelength cutoffs at 300, 285, and 230 nm respectively. These filter combinations correspond to exposures of electromagnetic radiation spectra simulating sunlight through glass, artificial sunlight, and nearly direct output from the xenon arc light source, respectively.

Light (3.8 hours) and dark (1.0 hours) exposures were alternated to simulate the radiative environment that occurs during the lifetime of museum objects. The average operating temperature in the Weather-ometer was 21�C, and the relative humidity fluctuated between 55% and 63% with the cycling.