I've just joined the group and was glancing through the last few days' emails.
You probably have more info than you need, but I'd like to offer you my solution, partially covered by the others.
I use mostly sable brushes along with a few bristle brushes, so I prefer not to use harsh cleaners, but good old "The Masters" Hand Soap for my brushes (not their brush cleaner) with as hot of water as I can stand. It's gentle, but gets out even long dried Maroger medium. Even an odd brush that's over-looked for a year can be cleaned successfully with a little patience. The hot water is with the soap is the key for sticky mediums. Fresh oil paint is cleaned in a snap and there is no residue left.
Then I wrap the very wet sable hair or the bristles of the brushes with cotton thread into the shape I want. This last tip is most useful, no matter your cleaning method, especially if you need a sharp tip for detail work or want to prevent fanning of in any brushes regardless of material. I only remove the thread just before I paint. Whatever shape I created with the thread holds throughout the next painting session, unless I purposely use the brushes harshly.
Cheers,
Ann
