This morning was my first trip to the Kingfield Farmer's Market. One vendor was a lovely woman, Kim Christiansen, who experiments with natural dyes and yarn. I was mesmerized by her booth, perhaps because it was 50 degrees and I wished I'd brought my handwarmers.
She explained that the color of a dye is a result of the dye substance, a mordant and the yarn itself. The mordant sets the dye on the fabric and different mordants can produce different colored results.
Pink yarn: Dyed with cochineal, a bug native to Latin America. Cochineal was used by the Aztec and Maya populations, later coveted by the Europeans. Cochineal are now cultivated on cactus plants and you can mail-order them from Oaxaca, Mexico. The mordant for this yarn was Rhubarb leaves! I don't understand what it is about the chemical properties of these two substances together that works, but Kim does.
Yellow yarn: Dyed with rhubarb leaves and stems.
Brownish yarn: Dyed with ivy berries and "unknown berries."
Green yarn: This one is my favorite. Kim was leading a group of middle school students in a chemistry of dyeing class to gather experimental dyes. One kid wanted to try buckthorn berries. This invasive shrub attacks yards and public lands in Minnesota. Its berries are a deep blue and are guaranteed to stain your sidewalk. but, when used as dye on merino wool, buckthorn berries leave a beautiful green. Another wool skein dyed with buckthorn was a lighter green due to the specific reaction between that wool and the berry.