Zinc white warning!

Richard Bingham · 09-19-2007, 05:20 PM

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?"

Gary Hoff · 09-23-2007, 09:16 AM

Quote:

Originally Posted by Richard Bingham

....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?"

Rich, based on what little I know (not a lot, and I have not read the original paper) the Mecklenburg study seems to miss the boat in accounting for variables like the substrates and the admixtures with zinc white. So any comments from here on, take with a grain of salt. Still, my two cents: delamination from acrylic-primed grounds has been amply demonstrated time and again; mixing one paint with another may often change not only the physical but the chemical characteristics of the paint. What it means to me is that if I paint a layer of zinc white on an acrylic-primed canvas, particularly if I paint it thickly, I risk cracking and delamination (duh). But mixing zinc white into a darker pigment is prolly not all that bad. Ho hum.

Richard Bingham · 09-19-2007, 05:57 PM

Intense!!
(I know you know your whites . . . )

David Clemons · 09-20-2007, 09:23 AM

The results of this report are nothing new, ultimately inconclusive, and rather superficial, in my understanding. The concern of the brittleness of zinc has been common knowledge for a long time. Even Ralph Mayer has that documented. The article also doesn't expand the results into other binders besides oil, like arcylics or watercolors, where zinc has been in use longer. The conclusions are only that it MAY point to early failure, and yet some early users of zinc grounds have held up well. To me, that is evidence of the need to examine how to use it properly, not cry that the sky is falling. One benefit of zinc in manufacturing is it doesn't darken when mixed with sulphur. My worry now is that companies will also react inappropriately. Lord help us if they start to look at titanium. We may be left with no whites at all.

David Clemons · 09-20-2007, 04:09 PM

There's no shortage of warnings out there from much older studies that zinc makes a brittle film. Some of them are footnotes to the article itself. I do appreciate that they spent 28 years to confirm what was already known, but it might have served us better had they expanded the study a bit more. Also, the delamination they observed apparantly only happened with oils applied to an acrylic primer.