I don't use preshave oil, but it's very possible it's come into contact with the alum.
Printable View
I'm pretty sure that's not the problem - mostly because it never used to ever be a problem with this brush, and I can still make great lather with my other brushes. Also, the difference between face and bowl lathering indicates it's not just a lather issue. I've definitely tried loading tons of soap onto the brush, it doesn't make a difference.