How do I know it's silk?
 

I recently bought two LARGE boxes of ties from the estate auction of a 93 year old quilter. More than 75 of them are labeled as all silk. Of the other several hundred ties there are labels on about 2/3 of them. I believe that some more are silk, but can't tell for sure. I don't want to mix fabrics in the projects I do with them. Some are cotton, wool, and acetate, but most are polyester. How do I determine the fabric content of the remaining 100 or so ties? Mostly I want to find those that aren't labeled but are silk.

I have recently acquired a large amount of ties also. I have found that even the ones that are labeled 100% silk wash up just like the cotton, poly cotton,and polyester ties. Because I put a light weight stabilizer behind all of the ties, I don't have any fears of mixing them in a project.

Crazy quilts have all different types of fabrics in them and they hold up well.

Your sense of touch should be able to weed out all but the best high end fake silk poly. Silk also has a distinctive smell. If you really can't tell after those two you can cut a bit and burn it.

Use the burn test to determine the fiber content. Silk will burn briefly and char, smells like burnt hair, and results in a black, soft bead. Synthetics melt. Here are a couple of excellent resources to help interpret the results.
http://www.pacificfabrics.com/media/...ile_Fibers.pdf
http://www.ditzyprints.com/dpburnchart.html

I cut a small piece of fabric and light a match to it. If the residue is ashy, it is organic such as cotton, wool, silk, etc. If the residue is hard and oily looking, the cloth is synthetic, such as polyester. If the residue is ambiguous, it is probably a blend.