For the cotton, I had several tea-dyed underpants that I wasn't wearing because I no longer have a need for this color and hate wearing white/natural underclothes unless absolutely necessary. I had five almost-new pairs of perfectly-fitting underpants sitting in a drawer. So I dyed them navy, leaving myself one pair in "natural" because I'm a just-in-case sort of person. I used 1 cup of salt in the dye bath and the fabric took the dye beautifully. I didn't expect the thread and elastic to dye.
I kept the water just under a simmer - at that point where tiny bubbles start to show at the bottom of the pot, but never get any further. I have never been able to "rinse until the water runs clear," but once I machine washed these (and the color runs a great deal that first time) and dried them, the color doesn't run any worse than store bought denim.
The silk long johns were the color "natural." I got them that color to wear under my wedding dress in case it was cold, but ended up not using them. I love silk long johns for under work clothes during the winter, but feel cranky when they are white/natural.
I put 1 cup of vinegar into the dye bath and kept the temperature just short of a simmer. When I went to rinse these before washing them, the water ran clear the first time and the color of the dye is beautiful. I think the light stitching adds a nice detail on the shirt neckline.
For a little over two hours of work, I now have clothes that aren't taking up space and that I look forward to wearing.
I'm still in awe at how easy and mess-free dying the silk was.