Duckster,

It is best not to exceed 140 degrees no matter what material you are dying,Lengthening the amount of time at a temp not exceeding this is what A.K.Best suggests no matter the dye used or color being applied..and is why dyeing things to darker colors such as black tend to make things brittle the extra time in the dye bath.
A.K. has a wonderful book on dyeing and bleaching natural materials...great read even if not going to do your own dyeing!

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"I've often wondered why it is that so many anglers spend so much money on,and pay so much attention to.the details on the wrong end of the fly line.If they took as much care in selecting or tying their flies as they did in the selection of the reel and rod,They might be able to gain the real extra edge that makes it possible to fool a fish that has,in fact,seen it all before" A.K.Best

Everyone wants to excel in this sport but at the same time we let traditionalists place restrictions on our tactics, methods, and ideas. I always assumed that fly fishing was a sport that allowed imagination, creation, adaptation, investigation, dedication, education, revelation? : Fox Statler, On Spinners (Not the dainty Dry Fly kind) "Spinner'd Minner Fly"

"Wish ya great fishing"

Bill