Congratulations!
After awhile, you will start picking up indicators that tell you if it is polyesther, a blend, or 100% cotton.
I am with Amma ... if I like a color or the fabric fits, I use it no matter what the blend is as long as the weight is similar.
fake fabric is polyesther (actually a byproduct of oil/gasoline)
I have found over the years, that I can tell by making a cut what I am working with - - cotton will cut cleanly ... polyesther starts wisping off on the cut edge ... and, if you are still not sure, give the edge of the cut a rub and see what happens next.
The burn test is the most accurate, I would suppose ... there is also a smell that happens with natural fibers burning ... like hair being burnt, while the other fabrics have an acidic, biting air.
The small beads from the burning of polyesther comes from the fact that they are oil-based ... it has been said that you could start fire to all the plastic in the world, and it would never disappear, it just shrivels on itself and turns into a ball!
I love plastic, don't get me wrong ... I have tried to figure out how to create an outdoor oven for melting all the plastic we have into some kind of rock for a retaining wall ... so far, my family thinks I am too crazy to even bother to try to fulfill my latest whim! :?