I am aware that it is possible that Zinc Oxide can cause delamination and cracking in oil paint layers. Unless there is some new information I missed, apparently there is no known safe amount of Zinc Oxide in the paint that will stop this for sure. I have read that less Zinc content is logically better if you do want to continue to use Zinc Oxide containing oil paint. I would appreciate hearing the latest from any of the moderators here who might want to comment on the following.
I have a large volume of Titanium White oil paint that has a Zinc Oxide content of 15% or less. I am not really wanting to throw it all away. I have decided to use that what only on rigid supports, but would also like to reduce the ratio of Zinc Oxide in it, if I can. Would it be worthwhile to mix existing Titanium / Zinc whites that have higher ratios of Zinc Oxide in them such as a known 15% maximum with Zinc free white paints and are there any lead free pigments such as PW5 / Lithopone or PW21 / Barium Sulfate that might be more apt to help reduce delamination and / or cracking?
On the same topic of the possible problems with Zinc, would it be advisable to avoid using acrylic underpainting layers when using Zinc containing oil whites? How about using oil grounds vs acrylic dispersion grounds with the same whites? And lastly, does the thickness of the layer containing the Zinc Oxide have any impact on the potential for cracking or delamination?
Thanks in advance for your input.
Thanks to all for your responses. I like the idea of giving the paint to someone who will use it in a learning situation and will tell them to get some zinc free white for working on future “keepers”.
Sorry for the delay. I was away from home for a few days. I have sent this question to a couple of our moderator who are more knowledgeable about these particulars.
To our knowledge there are no conservation studies that were dedicated to finding a safe level of zinc. In Sarah Sands research she found that decreasing zing content dramatically, going from 39% down to 3.6% did not change the brittleness of paint in most cases (see https://www.justpaint.org/zinc-oxide-reviewing-the-research/). We know of no pigment combinations that would prevent the embrittlement of zinc. Whether oil paint becomes more brittle when painted over zinc-containing acrylic paint layers, we currently don’t know yet but are investigating. We would not expect other acrylic colors of zinc-free dispersion grounds to cause adversary effects.
Thicker layers of zinc white oil paint would certainly cause more severe cracking and lifting. It would probably be best not to use your titanium-zinc paint on any artwork that you care about. Maybe you know somebody who is just starting out painting you could give that tube to.
Best,
Mirjam Hintz (Golden Artist Colors)
Without further research on the subject, as Mirjam mentioned by Golden Artists Colors, there is no reasonable assurance that oil paint containing any amount of zinc oxide will not rapidly embrittle. We started a study with different types of zinc oxide pigment, in different oils and in combination with other pigments to further study the behavior of zinc oxide in oil paint. In particular, we are studying the effect zinc oxide in primers has on an oil paintings. The results are still several years away.
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