THE U.S. FIRST LADIES GOWNS: A BIOCHEMICAL STUDY OF SILK PRESERVATION MARY A. BECKER, POLLY WILLMAN, AND NOREEN C. TUROSS ABSTRACT-The degradative changes in silk are are of interest to biochemists and bio-engineers investigated with amino acid analysis and solubility as well as conservation scientists. under denaturing conditions (7M urea). These Traditional textile testing methods such as biochemical techniques use extremely small samples measuring color difference and tensile strength for quantitative analyses and are capable of detecting have a limited usefulness in evaluating naturally chemical alterations at the molecular level. The aged fabrics with unknown histories. Although biochemical results are used to place the fabric color measurements can be made nondestruc- samples from a museum collection within the context tively, a color difference cannot be quantified of artificially aged silks. Analyses of the naturally aged because the original color is unknown. Tensile samples reveal two populations: sericin-rich and strength measurements require large samples by sericin-depleted. Denaturing solvents such as soap will remove the protective protein coating from museum standards and then provide evidence of sericin-rich fabrics; sericin-depleted fabrics are al- deterioration only after significant damage has occurred at the molecular level. ready a high risk for light-induced damage. The data suggest that silk fabrics manufactured during this cen- Previously, biochemical techniques were tury are likely to have their sericin coatings totally used to quantify the initial degradative changes removed and therefore at great risk to light damage. found in artificially aged silk fabrics. Quantita- tive results can be obtained from very small 1. INTRODUCTION samples. Becker and Tuross (1994) reported that the selective degradation mechanism In 1987, the exhibition of the U.S. First Ladies progressed to random destruction along the gowns, a popular and important Smithsonian molecular polymer chain with increasing length Institution collection, closed for renovation to of exposure and increasing energy content of allow the curatorial staff to reassess the the incident radiation. collection's use and to give conservators a This paper discusses how biochemical inves- chance for long overdue examinations and tigations are used to relate naturally aged silk treatments. This conservation project provided fabrics from a museum collection to artificially a unique opportunity for extensive collaborative research between scientists and conservators aged silk fabrics. The changes monitored in solubility and amino acid compositions are in- into the deterioration of silk, the material dicators of deterioration at the molecular level. predominant in this collection. The overall recovery of amino acids not only The scientific research focused on, first, the provides evidence of the extent of protein effectiveness of several analytical approaches preservation but also serves as an indication of with minimal destructive sampling as a means the state of preservation of the garment. of evaluating the object's state of preservation, A comparison between the overall amino and, second, the mechanisms involved in the acid composition of naturally aged silk and that degradation of silk. Since silk is a biopolymer, the effects of the environment on of both new, degummedthe silk (essentially pure fibroin), provides insight into the presence or physical and the chemical properties over time JAIC 34(1995):141-52 This content downloaded from 160.111.254.17 on Fri, 21 Sep 2018 17:48:24 UTC All use subject to https://about.jstor.org/terms 142 MARY A. BECKER, POLLY WILLMAN, AND NOREEN C. TUROSS absence of sericin, silk's natural coating. Museum The of History and Technology building presence of sericin and the impact of this (now NMAH) in 1964. Currently light levels protein on the state of silk preservation inwere areas displaying the First Ladies costumes are also investigated. 3 footcandles or less. Over the years the gowns in the First Ladies 2. HISTORY OF THE FIRST Collection have been subjected to various forms LADIES COLLECTION of museum and user handling as well as dif- ferent types of light. The collection is accom- The collection of costumes and accessories from panied by irregular historical documentation on the First Ladies of the United States of America the garments, covers a broad time period from is part of the Division of Political History at the 1780 to 1989, and consists of fabrics in variable Smithsonian Institution's National Museum of states of preservation. Of the 44 gowns on ex- American History (NMAH), Washington, D.C. hibit in 1987, 42 are constructed primarily of Fifteen silk gowns attributed to the First Ladies silk. of the White House were displayed as part of a The deleterious effects of light and dirt, as Period Costumes exhibit in the original U.S. well as the demands of long exhibition, are so National Museum building (now known as the serious that some of the gowns are now too Arts and Industries Building), opened to the fragile to be exhibited. The silk fabrics in the public on February 1, 1914 (Smithsonian gowns display a variety of museum-acquired Institution 1914). The term "First Lady," first degradative states. One example, Sarah Yorke used in 1860, is given to the "hostess" of the Jackson's wedding dress, crumbling at the hem, White House. Within just a few years, the was in such poor condition that now only the exhibit was declared "one of the most embroidered chiffon skirt is exhibited as part of interesting and popular in the Museum" a conservation section of the reopened exhibi- (Smithsonian Institution 1919, 66). tion. On the other hand, the silk in Barbara Of the original 15 silk gowns on display at Bush's gown is in pristine condition. the opening of the hall in 1914, 12 were still on display when the exhibition hall closed in 1987, 3. SILK: FIBROIN AND SERICIN and 11 had been shown continually during this 73-year period. The exhibit was initially lo- Silk fibroins (Howitt 1946; Lucas et al. 1958; cated in the west-north range of the Arts and In- Rudall 1960) are the extracellular proteinaceous dustries Building (A&I), where the gowns were filaments produced by certain species of the exposed to sunlight through large, west-facing phylum Arthropoda, classes Insecta and windows, although these windows were inter- Arachnida. Many species belonging to the class mittently protected by heavy curtains. In 1931 Insecta spin cocoons in which they pupate, such the exhibition was transferred to the north-west as the classic example, Bombyx mori (order range of A&I where they could be illuminated Lepidoptera, subclass Bombycidae). This with north light in order to make "artificial domesticated silkworm, actually a caterpillar, lighting of the collection unnecessary" (Smith- spins its cocoon after feeding on mulberry sonian Institution 1931, 12) (see fig. 1). leaves for nearly a month. The cocoon consists Daylight was not eliminated from the Collection of two extruded triangular-shaped filaments of a of Dresses of the First Ladies of the White House proteinaceous polymer called fibroin, held exhibit until the construction of a series of together by a gumlike protein called sericin. period-room displays in the 1950s. Reduction Removal of the sericin from silk fibroin is of artificial light levels was initiated during the accomplished by a process called "degumming," installation of the First Ladies Hall in the new usually by one of three methods: (1) extraction JAIC 34(1995):141-52 This content downloaded from 160.111.254.17 on Fri, 21 Sep 2018 17:48:24 UTC All use subject to https://about.jstor.org/terms THE U.S. FIRST LADIES GOWNS: A BIOCHEMICAL STUDY OF 143 SILK PRESERVATION Fig. 1. The First Ladies Hall in the Arts and Industries Building as it appeared around 1931. Photograph courtesy of the Smithsonian Institution, Washington, D.C. with water at high temperatures, (2) extractionproteins. Sericin, on the other hand, has over with dilute aqueous alkali or soap solutions, 30 mol or % serine (Komatsu 1980) and is readily (3) removal by proteolytic enzymes. soluble in hot, dilute alkali solutions (Lucas et A fundamental distinction between fibroin al. 1960). and sericin is the composition of amino acids that make up these two proteins (see 4.table MATERIALS 1). Characteristic features of the fibroins in general 4.1 FABRICS FROM THE FIRST are the high proportion of the smaller side LADIES COLLECTION group amino acids glycine, alanine, and serine and their insolubility in aqueous solutions. Fabric Thesamples were taken from several of the large percentage of the small side-chain gowns amino that had been on exhibit in the First Ladies Hall when it was closed for renovation acids allows for a close-packing arrangement of the molecules characteristic of the fibroins in 1987 and (see table 2). Whenever possible, is a general feature of extracellular matrix examples of silk fabric were taken from JAIC 34(1995):141-52 This content downloaded from 160.111.254.17 on Fri, 21 Sep 2018 17:48:24 UTC All use subject to https://about.jstor.org/terms 144 MARY A. BECKER, POLLY WILLMAN, AND NOREEN C. TUROSS TABLE 1 AMINO ACID COMPOSITIONS OF BOMBYX MORI SILK PROTEINS (mol %) AMINO ACIDS NEW HOT WATER SERICIN SILKf EXTRACT WHOLEt Glycine Gly 43.7 36.7 13.5 Alanine Ala 29.3 15.9 6.0 Serine Ser 10.7 11.9 33.4 Tyrosine Tyr 5.5 1.5 2.6 Valine Val 2.4 4.2 2.8 Aspartic acid/ Asx 1.8 10.9 16.7 asparagine Glutamic acid/ Glx 1.2 5.9 4.4 glutamine Threonine Thr 0.9 3.5 9.7 Phenylalanine Phe 0.9 2.8 0.53 Isoleucine Ile 0.7 3.6 0.72 Leucine Leu 0.6 2.7 1.14 Proline Pro n.d.