THE INFLUENCE OF MORDANT ON THE LIGHTFASTNESS OF YELLOW NATURAL DYES
Patricia Cox Crews
2 EXPERIMENTAL PROCEDURE
2.1 Sample Preparation
The fabric selected for this research was 100% worsted wool flannel, Style No. 525, manufactured by Testfabrics, Inc.11 It was a 2 × 2 twill weave and weighed 196 g/m2. The wool samples were scoured in a 0.5% solution of Ivory soap prior to mordanting and dyeing procedures.
The methods described by Hummel were generally used in the mordanting process.12 Quantities of the mordants and other agents used in the mordanting baths are given in Table I. Wool samples, weighing 454 g each, were mordanted at the boil for one hour, except for the samples with iron, which were treated for 30 minutes.
All dye plants were collected locally except fustic, indigo, and turmeric. The local dye plants were verified by the Kansas State University Herbarium. A list of the dye plants by common and scientific names is presented in Table II. Natural dyestuffs were extracted from the plants by soaking the plant material overnight in distilled water, then boiling for one hour, straining the dye and making up to 15 l with distilled water. Ten-gram specimens of the premordanted wool were dyed in the Launder-Ometer at 95°C for 30 minutes in 727 ml of the dyebath.13
YELLOW DYE PLANTS
2.2 Exposure to Light
Two wool samples were dyed with each dye and mordant combination listed in Tables I and II. A dyed wool specimen, measuring 7 × 20.5 cm, was cut from each sample and mounted in Atlas Fade-Ometer masks and exposed to light according to AATCC Test Method 16E-1978, Colorfastness to Light: Water-cooled Xenon-Arc Lamp, Continuous Light.14 Borosilicate inner filters and soda lime outer filter glasses surrounded the xenon-arc lamp. Blue wool standards were used to control the exposure periods as recommended by AATCC. Blue wool standards consist of a series of eight different blue-dyed wool cloths specially prepared so that each higher numbered blue wool standard is approximately twice as lightfast as the preceeding standard.15 Control of the exposure to light with blue wool standards instead of clock hours is recommended by AATCC and others to overcome the problem of variability of light source.16 The specimens were exposed to 5, 10, 20, 40 and 80 AATCC Fading Units (AFUs). After each exposure period, the dyed samples were evaluated for color change instrumentally.
2.3 Instrumental Evaluation
The color change in the exposed specimens was evaluated according to AATCC Test Method 153-1978, Color Measurement of Textiles: Instrumental. A HunterLab Color Difference Meter, Model D25 Signal Processor and Optical Head, with a Tektronix 31 Programmable calculator was used to measure color change.17 The instrument was calibrated with a white tile, Standard No. C2-8254. Color difference measurements were made for each specimen using a 2.54 cm viewing aperture with a 500 g load applied to each specimen for proper tensioning. The readings for both specimens representing each dye-mordant combination were averaged to yield the reported color change. The CIE L∗a∗b∗ formula was used to calculate the color change.
2.4 Visual Evaluations
The color change was also visually assessed by three trained observers following the final exposure period according to AATCC Evaluation Procedure 1, Gray Scale for Color Change. Visual assessments were made under simulated northern sky light in a MacBeth Lablite, Model BBX-526.18 Color change was assessed visually by two methods, one based on AATCC Fading Units with Gray Scale Ratings and one based on AATCC Blue Wool Lightfastness Standards.
The AATCC Gray Scale for Color Change was used to assess the color change on the dyed wool specimens after 80 AATCC Fading Units of light exposure. AATCC defines 80 AATCC Fading Units (AFUs) as the exposure required to produce “just appreciable fading” on AATCC Blue Wool Lightfastness Standard L6, regardless of the number of machine hours required to achieve this fade.19 “Just appreciable fading” is color loss equal to a Step 4 of the Gray Scale for Color Change.20
The color change was also compared to the AATCC Blue Wool Lightfastness Standards, L2, L3, L4, L5, and L6, and the colorfastness to light of a dye was classified as directed in AATCC Test Method 16-1978, Colorfastness to Light: General Method.21
2.5 Statistical Analysis
Three-way analysis of variance was used to measure the effects of dye, mordant, length of exposure, and their interactions on instrumentally measured color change.22 Duncan's multiple range test was used to further analyze the means of each independent variable when effects were significant at the 5% level.23