The word "Silk" refers to the excrement that comes from a "Silk" worm. The thread itself is not usually the problem, except for the laperdopus which isn't used for cloth. It is the "other stuff" that is a problem.
The "Silk" is spun, dyed, and woven into many different clothes.
If in doubt, go to a good mom & pop drugstore (we're boycotting the BBs) and get a bottle of distilled water, and litmus paper.
Place the cloth on a piece of rag mat board and drop a few drops of the distilled water onto the cloth untill you make a wet-spot (no giggling please) about the size of a quarter. Let stand about 15-20 minutes then with CLEAN tweezers, lay a litmus strip on the wet-spot and gently jam it into the spot untill wet/damp. If it changes color, compare to the chart that came with the litmus and you will know for sure about THAT piece of cloth.
Personally, I have yet to find a piece of silk that was more than 1 point off center.
For my age, that is pretty darn neutral.
baer