[Advances in Chemistry] Historic Textile and Paper Materials Volume 212 (Conservation and Characterization) || Mordanted, Natural-Dyed Wool and Silk Fabrics

Embed Size (px)

Text of [Advances in Chemistry] Historic Textile and Paper Materials Volume 212 (Conservation and...

  • 11 Mordanted, Natural-Dyed Wool and Silk Fabrics Light and Burial-Induced Changes in the Color and Tensile Properties

    Howard L. Needles, Vicki Cassman, and Martha J. Collins

    Division of Textiles and Clothing, University of California, Davis, CA 95616

    Light and burial-induced weathering caused significant changes in the color and tensile properties of natural-dyed and mordanted-natural-dyed wool and silk fabrics. The degree and nature of light and burial-induced changes on these fabrics were dependent on the fiber type and the dye or dye-mordant combination used. Dyed wool samples were generally more colorfast to simulated sunlight from a filtered xenon source than mordanted-dyed wool samples, whereas the dyed silk samples were rendered more colorfast to light by mordanting. Soil burial caused darkening and large shade changes in dyed wool and silk fabrics due to soil ion-induced mordanting. Dyed-mordanted samples underwent smaller shade and depth of shade changes than unmordanted-dyed samples on burial, and chromium and copper mordants had the greatest effect.

    DYE ANALYSIS IS AN IMPORTANT ANALYTICAL TOOL in the characterization of textiles of historical significance, but such analysis can be complicated by the aging process. Natural dyes found on historic textiles are not particularly lightfast or fast to soil burial conditions, and changes in the shade and depth of shade of dyed textiles can occur during these weathering processes. Mordanting of natural-dyed textiles with metal salts also can affect their color. In addition, the tensile properties of natural-dyed textiles can be affected by the dyeing-mordanting and weathering processes. Because the mechanisms of degradation are very different for weathering by light exposure versus burial in soil, color changes and changes in tensile properties are expected to differ depending on the weathering process used. The lightfastness of natural-

    0065-2393/86/0212-0199$06.00/0 1986 American Chemical Society

    Dow

    nloa

    ded

    by U

    NIV

    QUE

    ENSL

    AND

    on A

    pril 2

    8, 20

    13 | h

    ttp://p

    ubs.ac

    s.org

    Pu

    blic

    atio

    n D

    ate:

    Feb

    ruar

    y 1,

    198

    6 | do

    i: 10.1

    021/ba

    -1986-

    0212.c

    h011

    In Historic Textile and Paper Materials; Needles, H., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1986.

  • 200 HISTORIC TEXTILE AND PAPER MATERIALS

    dyed textiles also is of importance to the textile conservator because light exposure during display or storage can critically affect the color and the tensile properties of the textile.

    The lightfastness of natural dyes on fabric substrates has been the subject of numerous studies. However, the effect of mordants on the lightfastness of natural-dyed protein fiber substrates has received little attention. Some studies concerned with the effect of mordanting on the lightfastness of silk dyed with natural dyes have been conducted in Japan (1-3). Other studies have been concerned with the fastness of mordanted, natural-dyed protein fibers to artificial light as would be found in a museum setting (4-6). All these studies have established that mordants have a significant effect on the lightfastness of natural-dyed protein fibers.

    Archaeological specimens of historic textiles found in burial sites are often exposed to the most severe conditions; exposure to bacteria, yeasts, algae, and fungi causes severe discoloration and degradation to the dyed textile (7). Although certain metal salts are known to have antimicrobial properties, little is known about the effect of mordants on burial-induced color changes in natural-dyed protein fibers. Nockert and Wadsten observed that wool stored near metal objects or ornaments shows less degradation on storage (8). They concluded that soil fungi and other organisms are killed by metal ions and particularly by copper ions.

    To gain a better understanding of the effect of protein fiber type, dye, and mordant on sunlight and burial weathering processes, we dyed wool and silk with three phenolic dyes (found as major components in natural dye mixtures extracted from various plant sources) and post-mordanted samples of the dyed fabrics with five representative metal salts. We then exposed the unmordanted and the dyed-mordanted samples to simulated sunlight or soil burial and measured the differences in the color and tensile properties that resulted from these treatments.

    Experimental

    Materials. The wool fabric was a plain-weave worsted wool, style 6561, from Burlington Industries. The silk fabric was a degummed silk crepe, style 601, from Testfabrics, Inc. The dyes were >95% pure and were from the following sources: alizarin (C. I. Mordant Red 8) from Aldrich Chemical Co.; brazilin (C. I. Natural Red 24) from J. T. Baker Chemical Co.; and carminic acid (C. I. Natural Red 4) from H. Kohnstamm & Co., Inc. The five reagent grade metal salts used were aluminum potassium sulfate, stannous chloride, cupric sulfate, ferrous sulfate, and potassium dichromate from J. T. Baker Chemical Co.

    Dyeing and Mordanting Procedures. All dyeing and mordanting was carried out with a Renigal laboratory dyeing machine, model ST. Fabric pieces

    Dow

    nloa

    ded

    by U

    NIV

    QUE

    ENSL

    AND

    on A

    pril 2

    8, 20

    13 | h

    ttp://p

    ubs.ac

    s.org

    Pu

    blic

    atio

    n D

    ate:

    Feb

    ruar

    y 1,

    198

    6 | do

    i: 10.1

    021/ba

    -1986-

    0212.c

    h011

    In Historic Textile and Paper Materials; Needles, H., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1986.

  • 11. NEEDLES ET AL. Mordanted, Natural-Dyed Wool and Silk Fabrics 201

    measuring 33 X 25 cm were weighed and wet out in aqueous 0.05% Triton X-100, a nonionic surfactant, for 2 h prior to dyeing. All dyebaths contained 2% dye, 3% sulfuric acid, and 10% sodium sulfate on weight of fabric (owf), and a liquor ratio of 100:1 was used. The fabric was entered into the dyebath at 45 C, and the dyebath was brought to the boil and maintained at 100 C for 1 h with constant agitation. The fabric samples were thoroughly rinsed with distilled water to remove unfixed dye and were allowed to air dry. Each dyed fabric sample was cut into 18 pieces. Three swatches of each dyed fabric were mordanted with different mordant solutions. Each mordant bath contained 1% mordant (owf), and a liquor ratio of 100:1 was used. The three swatches were entered into the mordant bath at 95 C and were mordanted at this temperature for 1 h. The mordanted samples were thoroughly rinsed with distilled water and were allowed to air dry.

    Light and Burial-Induced Weathering Tests. Dyed and dyed-mordanted wool and silk samples were exposed to weathering by light and burial by using the American Association of Textile Chemists and Colorists (AATCC) Test Methods 16E-1982 and 30-1981, respectively, with certain modifications. In the lightfastness test, fabric samples were exposed continuously in an Atlas weather-ometer, model Ci35-W, for 80 h by using simulated sunlight from a filtered xenon source with a borosilicate interfilter and soda line glass outer filter operating at an average black panel temperature of 63 C and at an average relative humidity of 30%. During light exposure the samples received 85.6 kj/m2/nm irradiation at 420 nm. In the burial test, the samples were buried 2.5 cm under a sandy loam soil containing 25% moisture at pH 7 at 28 C for 14 days. The samples were thoroughly washed with distilled water and were air dried.

    Color and Tensile Measurements. The color expressed as x, y, and Y color coordinates and color differences () as measured for three or more samples by the AATCC Test Method 153-1978 using the CIELAB color difference formula and illuminant C were determined for all dyed and dyed-mordanted samples with a MacBeth MS-2000 color spectrophotometer. Tensile properties including breaking strength, percent elongation at break, and energy to break were measured for warp yarns from untreated and weathered dyed and dyed-mordanted samples with an Instron table model tensile testing machine by using a 1-in. gauge length and a crosshead speed of 1 in./min.

    Results and Discussion

    Mordant-Induced Color Changes. Mordanting had a profound effect on the shade (x, y) and the depth of shade (Y) of the dyed wool and silk fabrics (Table I). Alizarin, brazilin, and carminic acid all dyed the wool and silk to medium depths of shade.

    Alizarin dyed both wool and silk to similar shades and depths of shade. Mordanting caused the alizarin-dyed wool and silk fabrics to become darker and to change shades; wool gave the greatest color differences. Shade changes were similar in alizarin-dyed wool and silk samples mordanted with the same mordant. Mordanting with chromium, copper, and iron caused the greatest changes in shade and depth of shade.

    Dow

    nloa

    ded

    by U

    NIV

    QUE

    ENSL

    AND

    on A

    pril 2

    8, 20

    13 | h

    ttp://p

    ubs.ac

    s.org

    Pu

    blic

    atio

    n D

    ate:

    Feb

    ruar

    y 1,

    198

    6 | do

    i: 10.1

    021/ba

    -1986-

    0212.c

    h011

    In Historic Textile and Paper Materials; Needles, H., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1986.

  • 202 HISTORIC TEXTILE AND PAPER MATERIALS

    Table I. Mordant-Induced Color Changes in Dyed Wool and Silk Fabrics

    Wool Silk

    Mordant X y Y X y Y

    Alizarin 0.454 0.434 41.4 0.423 0.425 41.9 Al 0.433 0.358 27.9 37.0 0.399 0.347 28.3 35.