CA or resin type (boat finishes) will fail over time. Good start, stabilize the wood before application of finish. Minwax makes a pretty good wood hardener. As far as CA finish goes, use a very thin type for the first couple coats so you get penetration, then go on to a medium CA for build (it'll give you that depth you're looking for). Once you are satisfied with the amount of coats, maybe 6 to 8, sand and polish. I usually go up to 1500 grit, then polish it with compounds until it looks like glass.

Can't wait to see the finished brushes..... especially the burls..
Good work.