Zinc white warning!

Sharon Knettell · 09-18-2007, 07:32 PM

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Pam Powell · 09-19-2007, 01:08 PM

Thanks for the invaluable info! The article made the case quite clearly and scared the bejebees out of me.

Richard Bingham · 09-19-2007, 03:55 PM

Quote:

Originally Posted by Pam Powell

. . . The article . . . scared the bejebees out of me.

Good. That's what it was meant to do. Lead white? Lead is poison. So is turpentine and a number of the other pigment stuffs, solvents and vehicles used extensively through the last 500 years. Linseed oil yellows, resins cause paint failures, and we are all doomed. Doomed I tell you!

TRVTHS: 1. Lead carbonate + linseed oil = the most durable, long-lived paint films.
2. All oil paint mixtures will eventually dry to become a brittle, inflexible layer. As it dries, stresses due to the materials and behavior of the painting supports, underpainting layers, overpainting layers, leanness/fatness of those layers and the pigment stuffs employed may cause cracking, separation of paint from the ground or support, and various other failures.
3. It's really difficult to screw up a painting so badly as to see obvious, drastic failure inside of ten years.
4. Zinc white is relatively new in the armamentarium of oil painting, having been introduced in the last 150 years or so. Numerous paintings employing it have been painted during this time, which are in reasonable condition, but if you use VanEyck for a yardstick of permanence, the jury's still out.
5. If there's any advantage to using zinc white, perhaps it would be to provide the transparency of a lead white with a "non-toxic" material.
(I wonder who eats all the paint?)

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?"

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.

Linda Ciallelo · 09-20-2007, 08:53 PM

Sharon, I just learned that Michael Hardings Flake white #2 is now ground in saflower oil and the flake white#1 is ground in linseed oil, but both contain a small amount of zinc. I paint on canvas covered masonite that is lead primed, so I'm safe. The Michael Harding website is a little misleading as to what oil it's ground in. I bought both kinds of Flake white and read the label. I prefer the flake white #1 because it dries faster.

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.

David Clemons · 09-23-2007, 10:21 AM

Quote:

Originally Posted by Sharon Knettell

David, I apologize...

No need to. I'm glad you see my point.

A study like this does have merit in order to demonstrate concerns, but it pays to be somewhat skeptical. As you have said, many folks out there use acrylic primed surfaces; probably MOST that is sold is universal pre-primed canvas stock, I would think. I hardly ever use an acrylic primer, myself, and would never consider it for oils, zinc or otherwise. But, that's just me. Of my own oil paint inventory, none of the whites are exclusively zinc; most are mixtures. I do have some issues with the conclusions they made: "For the time being, it should only be used in paint where the objective is not archival." I think caution is advised, but not complete ommision of zinc content. It depends on how you use it.