I’ve mentioned this in another thread, but haven’t actually phrased it as a question, and I am curious what the MITRA folks think about using a thin sizing of Paraloid B-72 to reduce the absorbency of either Claybord or traditional gesso, prior to painting with oils. I mean, I know that it works, from a process standpoint, but is it a sound practice?
My own research on Paraloid B-72 suggests that it is one of the more stable synthetic resins and is not prone to yellowing, but like all acrylics, it is somewhat sensitive to solvents. Then again, it’s incorporated into the ground (which in the case of Claybord, already contains acrylic resin), so is it really any worse than painting on an acrylic primer?
What you write is perfectly logical. It will cut the absorbency of a true gesso ground while changing its characteristics and making it slightly less water soluble (also less friendly for egg tempera) . B-72 is no worse, and generally better than most of the acrylic polymers used in synthetic binders. It will remain soluble in the same solvents that it was initially soluble in. That is both its virtue and a slight deficit for other reasons like these. For most situations that you mention, it should be an admirable sizing layer.