I use Andrea solo viola and Bernadel light violin rosin. On fresh bow hair, which would you apply as a 'base'?
I think you're overthinking things.
I don't know if this has any basis, but I think it relates to David's question: The new ANDREA Sanctus rosin cakes are fairly large and have a central core of softer rosin surrounded by an outer layer of harder rosin. The cakes are sold in 3 grades: violin, viola and cello. Supposedly they are put 2 hardnesses of rosin on the bow hair at the same time: obviously, harder first followed immediately by soft then hard again. This would give you ANDREA Symphony - ANDREA Solo - ANDREA Symphony.
Some people use bass rosin lightly to get the hair to catch whatever lighter rosin they want to put on. This is especially common with synthetic bow hair, since it's less grabby than the real thing.
Use whatever rosin you intend to use on the bow on a routine basis.
Thanks for your responses. As soon as I apply the second rosin, I accept that there will always be some sort of blend. I used the 'softer' rosin as a 'base' because the seasonal humidity is lowering. Perhaps the properties of rosins are close enough that it doesn't matter which is applied first. (Unlike ski wax)
I wonder if you could use a miniature vacuum cleaner, such as is used to clean motherboards and the like, to clear rosin dust from bow hairs.
A dry toothbrush and/or a microfiber cloth will do the job as well as anything short of liquid solvents and detergents. As I understand it there is a surface attraction of rosin to hair and string that would beat anything a vacuum (which is just wind or wind and brushing-if your vacuum had a brush) could do.