Each week, we are emailed with questions from our natural dye community asking simple and complex questions that we thought might be worth sharing. Here are a handful from this week answered by natural dyer in chief, Kathy Hattori, Founder of Botanical Colors:
What’s the difference between colorfastness in natural dyes vs synthetic? Based on the fact that we have museums filled with tapestries and other textiles from hundreds of years ago, why is there such debate that natural dyes last?
This is an interesting question with a complex answer. Color, light and washfastness commonly refers to how well a dyed textile performs when exposed to light, moisture, abrasion and perspiration and is a standardized measurement. In its current definition, the standard is based on how well a synthetic dye performs when the textile is put through typical use. For example, if you purchase a bright red t-shirt from your favorite store, you want to be reasonably assured that it will not run, fade or discolor from perspiration over the first year of use.
In the recent past, synthetic dyes often did not perform well, and it was common to have the dyes fade, bleed and change color. Synthetic dye manufacturers improved the dyestuffs and now most synthetics that are used for mass manufacturing have improved performance as well. In addition, the dyes are now created for specific fibers, so there are synthetic dye classes specific to cellulose, protein and polyester fibers that are distinct from each other.
Current use of natural dyes is a bit of a free-for-all since one can use everything from coffee grounds to rose petals to make a color on a textile and many of these dyestuffs are not robust at all. There is nothing wrong with this; there is great value in walking out into your garden and harvesting dye colors like you’d pick a ripe tomato. I think it brings us closer to answering questions about where our clothing and colors come from and that is a vital discussion in our throw-away consumer culture. However, the textiles that have been preserved in museums are commonly dyed with the natural dyes that have literally stood the test of time: Indigo, madder, cochineal, walnut, weld and a few others. When these colors are put through standardized textile tests, they perform very well and pass with “flying colors.”
My take on this debate is that I don’t think that this is the “issue” with natural vs. synthetic dyes. Any dye that is improperly dyed will run, fade and bleed whether synthetic or natural. I also have a Twinkie shelf life flashback when I hear about someone touting the performance of synthetics against natural dyes. My sense is that a Twinkie will easily outlast a home-baked muffin in terms of its shelf life but do you really want to eat that? We should make our color and dye decisions based on other considerations.
I think a more interesting issue to think about is: are the dyes that are being used creating a lower or higher environmental impact? Are they safe? What’s the real cost? How much water and resources did it take to dye this garment? Did someone suffer to make my clothes? It’s more interesting to ponder these questions than to engage in an internet fight over synthetic vs natural dye lightfastness. There are more serious issues to consider.
Does leather dyeing require mordants?
The leather tanning process uses tannins and these function as mordants. Each tannin has a specific use depending on the animal skin and the desired tanning effect, In some cases, aluminum sulfate is also used to dye leather.