Some glass painters use oil based mediums, e.g. lavender, turpentine, kerosene, for matting. When you're done blending those media, do you clean the badger brush with mineral spirits? Do you clean it the way I envision doing it: just working the tips of the hair in the solvent and then using soap and water to remove the solvent? Do you dedicate a blender just for oil use?
I use separate blenders for oils. I've used them primarily for clove oil and lavender oil.
I clean the blenders using "The Masters" Brush Cleaner and Preserver soap tubs available through art supply stores. The soap is designed to remove paint oils, like linseed oil, while being gentle on brushes. I suspect this is a better approach than using chemical solvents. The brushes clean up very well.
A tip I received for longer blender life is to wet and clean only the tips of the blender hair that are exposed to the oil--keeping the rest of the brush as dry as possible. This is done by protecting the base of the brush with the hand when washing and rinsing.