With blends of plant fiber fabrics, the blended fibers will remain. Make sure there is a bucket of water nearby and that you burn in a metal bucket or non-plastic sink. To identify fabric that is unknown, a simple burn test can be done to determine if the fabric is a natural fiber, man made fiber, or a blend of natural and man made fibers. The burn test is used by many fabric stores and designers and takes practice to determine the exact fiber content. This elimination process will give information necessary to decide the care of the fabric.
Asbestos treated fibers are, for the most part fire proof.
The burning test should be done with caution. Use a small piece of fabric only. Hold the fabric with tweezers, not your fingers. Burn over a metal dish with soda in the bottom or even water in the bottom of the dish. Some fabrics will ignite and melt.