Turkey Red Journal
Dye Terminology: The F’s: Fast versus Fugitive
Pat Slaven
For dyes, "Fast" means that a dye forms a chemical or mechanical bond with the fiber and does not wash off nor does it fade in light. For natural dyes, the mordant assists in the chemical bond. Sometimes there will be qualifiers, such as the dye is generally fast to washing or it is good in light.
"Fugitive" means the dye isn’t fast.
Still fugitive dyes hold some intrigue. Sometimes the fading of natural dyes is called "mellowing", which is a more neutral word than fugitive.
So we can say a dye is fast, but to what? This statement begs the question: fast to light or to washing? While many mordanted natural dyes are good for one of these properties, it is rare to be good for both. Many natural dye tomes provide the standard suggestions to use dyes with good lightfastness properties for textiles that will be in sunny locations like wall hangings or curtains, while any garment that will be regularly washed or an item that will be felted needs washfast dyes.
Technically lightfast means that the chromophores (colorant in the dye) do not photodegrade in ultraviolet light. In other words, they do not break down or bleach out in sunlight. This property is commonly tested under Xenon light using American Association of Textile Chemists & Colorists (AATCC) Test Method 16 c, Colorfastness to Light: Xenon-Arc. This technical test compares color loss of a dyed substrate to the standard Blue wool scale to evaluate lightfastness. This scale is composed of 8 steps (8 is the most light fast and 1 the least). Lightfastness is evaluated comparatively for up to 22 hours of exposure in the Xenon light box. The evaluation can also be with done with instrumentation or the AATCC Grey Scale for Color Change, where 5 is no color change and 1 is significant color change evaluated in 9 half-steps.
The issues with dyes that are not washfast are color bleeding onto other textiles in wet processing (laundering) and the progressive fading from dye loss with successive laundering. Washfast is technical color change caused by laundering: the dye is slowly (or not so slowly) leaving the textile and going back into solution. It is determined using the AATCC Grey Scale for Color Change, where 5 is no color change and 1 is significant color change evaluated in 9 half-steps, or by instrumentation. The evaluation is typically done after five care cycles. There are other test methods but the evaluation is the same. AATCC Test Method 61 Colorfastness to Laundering: Accelerated, is frequently used.
Both the Colorfastness to Light and the Colorfastness to Laundering tests are laboratory evaluations that approximate color and indicate the dye’s tendencies in normal use.
Most natural dyes are neither washfast nor lightfast in their pure form. Again, mordants improve the chemical bond between the dye and fiber to improve washfastness and lightfast properties. Indigo is a rare natural dye that is both washfast and lightfast. It is the traditional color of Navy uniforms for this reason, as these garments are exposed to water and light on a regular basis.
Some natural dye recipes provide some indication of washfast and lightfast properties. As previously mentioned, many books on natural dyeing skirt around the particulars of colorfastness with a blanket statement that mordants help, but there are usually few details particular to specific dye stuff or mordants. Rita Adrorko, in Natural Dyes and Home Dyeing (1971), does provide information on both the washfast and lightfast properties for numerous natural dyes, often with and without common mordants. Ms. Adrorko also provides the recommended mordant recipes for each dye stuff. This book remains a good resource for any dye library and can still be found in libraries, from used book dealers and online.
In Closing
Visit the Cloisters in New York City and sit for a while with the Unicorn Tapestries. You can find these in books too, but the museum is truly worth the trip. The leaves on the flowers and trees are much more blue than green today. Indigo is very “Fast” to both washing and to light. The yellows on the other hand are neither, especially after an estimated 500 years of hanging on various walls or covering potatoes. These tapestries are a testament to the intersection of Fast and Fugitive. Were they more brilliant 500 years ago? Well yes, but we continue to enjoy them in 2019. In your own work, it pays to consider the effects of washing and/or light fading when you choose the dyes you use.
Happy dyeing, Pat Slaven
References:
AATCC (American Association of Textile Chemists & Colorists) Technical Manual
Rita Adrorko, 1971. Natural Dyes and Home Dyeing
About the Author Pat Slaven is a Chemical Engineer and Textile Chemist who worked for a carpet care trade association and later for Consumer Reports. She is an occasional contributor to Shuttle Spindle & Dye Pot, is active in the Handweaver's Guild and her local knitting guild. And yes, she dyes a lot of fiber.
If you have ideas for future Dye Terminology columns, please forward them to Pamela Feldman at madder@comcast.net.