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I've gotta get hold of some of that "nanospheres" white, just to see what all the fuss is about. Honestly, I didn't know SP was offering a "nano-zinc", I thought the spheres were being added to flake white. (??) For my part, I'm a "lead guy" . . . happy as apig in mud, and unwilling to leave the sty, now that I've recreated my favorite lead white.
That ashen, pasty, chalkiness you mention is often the function of mis-using titanium, which is about as opaque as oil paint ever gets. I think a lot of people painting don't even know this difference in the properties of whites.
As for questioning whether admixtures of other materials or pigments would obviate a "natural" brittleness of zinc white, that would be a possibility. Think of asphalt as a metaphor for paint. The tar is the "vehicle", the gravel is the "pigment". If zinc white results in a "naturally brittle" paint film (I doubt that) it would be owing to a chemical reaction between the pigment stuff and the vehicle. It could make certain grades or methods of manufacturing zinc oxide suspect. "Cutting" the zinc content would reduce such a reaction. Possible example would be Weber's "Permalba" which is a zinc mix first marketed in the early 1920's. If it were not reasonably archival, 80+ years is plenty long to determine that. I have several paintings pushing 70 painted with Permalba that are not cracking.
As for the Pre-Raphs, it's my understanding they liked to paint wet-in-wet, full color into a layer of zinc white . . . did the methodology circumvent the "nature" of zinc to crack . . . ?? I'll have to do a little reading, but my impression is the Raphs, like most painters, used a variety of substrates. Of course a rigid support will lessen the possibility of brittle films cracking due to movement in any case, and eventually, ALL oil paint films will be brittle as glass.
The article makes it sound as if there are no variables, nor mitigating circumstances. There is no material that cannot be mis-used to failure, just as there is no material that can safely be identified in all its manifestations of quality and sources generically. Quoth the maven, "What's the score?"
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