Does anyone know what exactly the burn test is when it comes to finding out if a cotton towel is really 100% cotton? I thought it was if you see a regular flame, then it's 100% cotton. But if all you see is black smoke and melting fibers, then it's not. Is this correct? I tried burning 3 different towels the other day and they all burned the same way. I can't tell if they would be considered cotton or not. The flame looked like a regular candle flame and the towel fibers quickly became black. No black smoke. I should note that one of these towels was 85% cotton/15% polyetser, which leads me to believe that maybe the other 2 towels are really not 100% cotton even though they say they are?