My Dear Franklin -
As related by our Good Major2, The Object of Your Desire is Bickmore Kahl Hat Stiffener or thinned white shellac.
you would do a disservice to your hat to use anything else (such as spray starch or scotchguard)
from Del, long ago:
http://www.theopenrange.net/forum/index.php?topic=5513.5"If you don't have some hat stiffener, get some. If you don't have a local source, think again, if your local Western Store don't carry it, get some white shellac (the natural kind) and some denatured alcohol and a spray bottle. Mix it about 50/50 or till it sprays nice, too thin is better than too thick"
"Scotchguard is not good for using as hat stiffener, I've seen a lot of them that it was used on crack, hat stiffener (aka shellac cut with denatured alcohol) is the only thing you should use. That is what all hat makers use, if there was something better they would use it."
and his long version here:
http://www.cascity.com/forumhall/index.php/topic,11542.0.htmlyhs
prof marvel