Boar knot

Well, that I think depends on the ambient conditions. Here now it's in the 100's and I dry it on the window sill exposed to the wind, so I would assume it wouldn't take 4 days to dry.

Someone on another forum mentioned using a hair dryer to cause boar hairs to split. I tried it on a cheaper boar and it works. You just have to make sure to not keep the dryer on it too long and to keep it focused on the tips (not the bottom of the knot, where it could damage the glue).

However, my Omega and Semogue boar brushes never needed this treatment. The started off good and got progressively better rather quickly.

I'm not sure why your boar brush hairs split so suddenly, but perhaps it was time or just a cumulative thing. Either way, that's great. I love a well broken-in boar.

A gent on another forum spent 30 minutes or so with a rubber sheet and a brand new Boar to break it in. He claimed success with just working it wet on the rubber.