I suspect you charred the char right out of it.
Spot on! I can see from here that bath towel was overcharred.
Think of it as a continuum between not charred enough, just right, and overcharred.
Let's take this piece by piece...
I cut up a piece of 100% Cotton Terrycloth bath towel
Good choice. Thicker and more tiny edges tends to work better.
put it in an Altoids tin,
Not the best choice, but they do work. They work slightly better without additional holes.
put it in my gas forge and got it up to a dull red and
Making the tin glow not only is more heat than needed, it unnecessarily hastens the diminishing of the lifespan of the tin. Also, the higher the heat the more narrow the window between not charred enough, just right, and overcharred. Can be done but it requires a finer touch.
held it until it quit smoking.
While most recommend that, and many find that it does work, I have long found that by the time the smoke stops it is already overcharred. I watch for maximum smoke output and as soon as that noticeably decreases, take it off. Remember that it continues to char until cool. Also that undercharred materials can be charred again. Once overcharred there is nothing we can do.
Except it was crispy to the touch and will NOT catch a spark.
Properly charred materials retain most of their original structure. Thus properly charred cloth is still flexible, tears with an audible ripping sound and has very little soot on it. Indeed, the less sooty the better as soot is merely overcharred dust. Overly sooty fingers when handling are a sign of poor char.
I will be looking for another source of 100% cotton, too.
Perhaps a hasty decision. Once you are able to char pieces of this towel more optimally, only then will you be able to tell whether this is a good source for char or not.
Hope that helps.
Cheers!
