Loss of white lead led to increased use of silex and or clay in dry powder form. Has anyone given any thought to the use of the micro balloon powders that are available and commonly used as filler in epoxy. These are air filled spheroidal shapes in various materials. The two that come to mind that may be of interest are glass and phenolic. Glass of course is silica the same thing that silex is only in a hollow ball shape. Phenolic is a water proof resin that is also used in some varnishes. Both are availble as "powder" and could possibly used as light weight bulk to a traditional linseed oil based filler. Those that are using latex based fillers and light weight spackle are already using silica micro balloons as that or something very similar is what is used as the filler. Anyway just some thoughts for consideration.