In article .com,
says...
Meaning, either crackly, or different flame colors, or (i've seen at
some point) very bright white embers burning in the draft.

Not the best for any metal flue or damper, but driftwood taken from
sal****er tends to have multiple colors because of the salt.

--
is Joshua Putnam
http://www.phred.org/~josh/
Updated Bicycle Touring Books List:
http://www.phred.org/~josh/bike/tourbooks.html