Prickly pear fruits yield the most gorgeous, luscious, magenta juice that you can imagine. Naturally, when I'd juiced a batch for jam-making, I wondered about dyeing with them!
The pigment in prickly pear is betalain, which is the same pigment that gives beets and bougainvillea their lovely, deep, purplish reds. Betalain turns out to be a rather unstable dye-source, as its sensitive to both light and heat.
But the juice color was too deep and seductive to pass up! And anyways, I thought prickly pears might still be a good candidate for dyeing, since you don't have to heat them to get juice.
I soaked alum-mordanted alpaca/wool yarn in straight juice overnight, and I got this enchantingly deep magenta yarn. The picture doesn't begin to capture the richness and saturation of the color. Truly one of the most beautiful colors I've ever gotten with my natural dyeing.
And then (sigh) I went and tested it for lightfastness. I started with samples of three naturally-dyed yarns -- (1) a light lilac from local cochineal on alum-mordanted yarn, (2) a medium magenta from prickly pear on unmordanted yarn, and (3) a dark magenta from prickly pear on alum-mordanted yarn -- and hung them, half-enclosed in cardboard, on a south-facing fence. There they got a three-weeks' dose of good, strong Arizona sun.
And here's the big reveal - such drama and disappointment! The prickly pear dye disappeared from the unmordanted yarn and faded to a dull peachy tone on the alum-mordanted yarn. Interestingly, the cochineal faded more than expected, too, although it's to be noted that I used strange little cochineal scraped from neighbors' cacti rather than cochineal that was specifically prepared for dyeing.
After this debacle, I found some terrific old books on Native American dyeing at a used bookstore. The prickly pear recipes in those books had the yarn fermenting in prickly pear juice for several days; perhaps it is worth trying this experiment again with that method. I think, though, that from now on I will enjoy my betalain in the bougainvillea....