I found a wonderful chart at http://nvg.org.au/. The New Varangian Guard Inc. (NVG Inc) is a historical re-enactment organization with branches throughout Australia, and sister organizations in several other countries. I am copying the chart below and giving them credit since the original source of the information is a dead link.
How to tell what the fiber is:
Snip a piece of fabric equivalent to 1" square. Using butane lighter and holding the fabric with a pair of tweezers ignite the fabric over a non-flammable surface in a well ventilated area.
Examine the quality and color of the flame, the odor produced, and the quality of the resulting ash or cinder.
Use this table to help determine your fabric's content.
|FABRIC||FLAME QUALITY||ODOR||ASH QUALITY||COMMMENTS|
|WOOL||orange color, sputtery||burning hair or feathers||blackish, turns to powder when crushed||flame will self-extinguish if flame source is removed, no smoke|
|SILK||burns slowly||burning hair or feathers||grayish, turns to powder when crushed||burns more easily than wool but will self extinguish is flame source removed|
|COTTON||yellow to orange color, steady flame||burning paper or leaves||grayish, fluffy||slow burning ember|
|LINEN||yellow to orange color, steady flame||burning paper or leaves||grayish, fluffy||takes longer to ignite than cotton, but otherwise very similar|
|RAYON||fast orange flame||burning paper or leaves||almost no ash||will continue to burn after flame source removed|
|POLYESTER||orange flame, sputtery||sweet or fruity smell||hard shiny black bead||black smoke|
|ACETATE||burns and melts, sizzly||acidic or vinegary||hard black bead||will continue to burn after flame source removed|
|NYLON||burns slowly and melts, bluse base and orange tip, no smoke||burning celery||hard grayish or brownish bead||will self extinguish if flame source removed|
|ACRYLIC||burns and melts, white-orange tip, no smoke||acrid||black hard crust||will continue to burn after flame source removed|
To determine content of fabrics I recommend conducting this first with fabrics that you are sure about the content of – so you will know the outcome of the test yourself. In a non reactive pan (I use a pyrex pie plate) take snips (small pieces) of the fabric you will be testing. Use straight bleach and put about ½” of bleach in the pan. Please do this in a ventilated area. Add the snippets of fabric and let them sit for about 24 hours. The next day, look at what you have left.
|100% Linen or Cotton||any color should be removed from the fabric, but there will be no damage to the fibers themselves|
|100% Silk or Wool||the fabric will have fully dissolved (unless its worsted/gabardine, there is a fabric treatment that protects the fabric from the bleach and keeps the fabric shiny even after washes).|
|100% Polyester, Rayon, Acetate, or Nylon||the fabric will have become a cloudy mess within the bleach. Fully dissolved into an opaque cloud within the bleach.|
|Blends –||The individual fibers will act as described above. The result will be different for each combination|
|Rayon / Linen||linen fibers with a opaque cloud;|
|Silk / Polyester and Wool / nylon||fully dissolved with an opaque cloud;|
|Linen / Cotton||no damage to the fibers;|
|Silk / Wool||fully dissolved.|