Bleaching silk

I’ve been doing some experiments in bleaching silk. I need to dye some silk bright lemon yellow for my next project. In the past, I’ve had trouble getting bright lemon yellow because natural/unbleached silk is actually a very pale brown. This makes (essentially) no difference for dark or dull shades, but for pale colors, and especially pale bright colors, it dulls out the color.

I posted to WeaveTech (I think it was WeaveTech) a few weeks ago in an effort to find a good recipe for bleaching silk. I got referred to two recipes. One was Treenway Silks’ proprietary recipe, which they were generous enough to share with me (but, of course, requested that I not share with others). The other was ProChem’s recipe for bleaching wool and silk. The ProChem recipe involves heating a solution of hydrogen peroxide, water, Synthrapol (a detergent) and soda ash to 130 degrees and then soaking the fabric/yarn in it for 16-24 hours.

I tested both methods, and since I had seven skeins to dye, I used one as a control (unbleached) and used three each to test each recipe – leaving the silk in the bleaching bath for 2 hours, 8 hours, and 24 hours.

Results? Both methods bleached the yarn without noticeable loss of luster (haven’t tested strength yet). Treenway’s method worked faster and more completely than ProChem’s, although after 24 hours in the bath the difference was barely detectable.

Here are sample cards from the first skeins to emerge (the others are still drying):

I had a really hard time capturing the color differences, since they are quite subtle. In this photo, the differences are exaggerated – the “real life” color of the ecru yarn is closer to the color of the cardboard in the center card, and the Treenway method sample is a bit paler as well. However, there is a noticeable difference between the three cards, with the unbleached skein looking a bit more dingy. The ProChem method sample is also noticeably darker than the Treenway method sample.

It’s hard for me to report definitively on the later baths because the yarn is not fully dry yet, and colors will shift as a yarn dries. However, it looks like the ProChem method continues to bleach after the first two hours, while the Treenway method is fully bleached after two hours (or possibly less). Once 24 hours have gone by, there is still a difference between the two skeins (Treenway’s method is whiter) but it is barely perceptible. (As in, I can pick it out if I look really hard, but I’m not sure most people could tell the difference – I have a pretty sensitive eye for color.)

My next step, after the yarns are fully dry and I have wound sample cards from the later baths, will be to dye three skeins bright lemon yellow. (I need three skeins of yellow for my project!) Those will be the unbleached skein, the Treenway method 2 hour dyebath skein, and the ProChem 24 hour dyebath skein. I am guessing that there will be a perceptible difference between the unbleached skein and the two bleached skeins, but the difference between the bleached skeins will be imperceptible. Primarily what I’m trying to see is whether either bleaching process impacts dye take-up. I am guessing that neither affects dye take-up, since Treenway developed their method with the intent of dyeing the yarn after bleaching, and ProChem (being a dyehouse) probably did the same.

In the end, if the two bleaching methods produce comparable results, I’ll use Treenway’s method, because it’s faster than the ProChem method (which really does require 24 hours to bleach fully), and I suspect it may also be easier on the yarn due to the nature of the recipe.

My intent for all of this is to find the right bleaching method so I can pre-bleach the yarn for the kimono. I want the brightest color possible, and in particular I want the lemon yellow of the top phoenixes to stand out clearly. Thus, the experiments with bleaching processes.