Cosmic_Charlie;
I looked on a couple of sites that have made extensive charcoal tests, and they didn't have Aspen listed. But, Aspens are part of the Poplar family, and White Poplar made fast charcoal, for the tests they made, here:
http://www.wichitabuggywhip.com/fire...oal_tests.html
I was surprised nobody (that I have read of) has tried Aspen. As light and fast burning as it is, and as little ash as it produces in burning, it would seem that it should make great charcoal, for our use. You might build a fire, and take a piece or two of the charcoal and test it for ash. If it is low ash content, give it a try. It would be interesting to see if it is good, or not. If you do try it, be sure and let us know how it tests for you. If you read over the link above, it lists about 80+ different woods which they have tested for burn rate, and lift (power). Bear in mind, they won't say much about cleanliness of burn, because they use powder for fireworks, and clean doesn't matter much.