The other day I dyed a pair of identical silk crepe scarves a yummy avocado. They went into the same dyebath and when I'd finished washing them out and drying them, they looked identical, and lovely.
But they were a little bright for wearing, so I decided to tone them down a little. To check they matched what they were intended to go with, I ironed one of them, since crepe catches the light a little differently if just dried on the line vs. being ironed out. The match was fine.
So into a new dyebath they both went. When I'd finished processing them, I noticed that the one I had ironed had taken up the pale black dye much less than the un-ironed one, which looked noticeably a tone darker. See this picture of the two of them (the un-ironed one is on the left, the ironed one on the right):
Why would ironing affect the silk this way? Is it because it was silk crepe (somehow its crepe got completely flattened by the iron? its surface was different now for the uptake of the dye?)? I was completely astounded (and frustrated, of course, since they were supposed to be a pair!).
--Pia in Seattle