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Question asked 2023-09-26 13:50:59 ...
Most recent comment 2023-10-28 11:16:49
Oil Paint
Hello all,
Curious whether anyone can offer some insight into a frustrating experience I just had in the final stages of an oil painting. I'm using Gamblin's Solvent-Free Medium for the first time. It worked great with the first coat. In the second layer, however, flat areas of color painted with the exact same color mixtures that I had used previously and saved, dried with darker and lighter patches. I spoke with Gamblin and they said this had nothing to do with the medium. They said it was a well-documented phenomenon with color mixtures that have a lot of titanium white in them, which mine do, sometimes called Voodoo Darkening. This palette is not unique to me though, and I've never had this issue before.
Gamblin recommended I remix the colors with Zinc white and completely repaint the problematic passages using Solvent-Free Medium. Before such a risky and laborious undertaking, I'd love any feedback anyone can share. Is it really my old friend Titanium that's causing these issues and NOT the brand-new medium I'm using?
I should add that the work is on high-quality linen stretched over a Gatorboard panel. The oil layers are on top of an acrylic underainting.
Thanks so much,
Aliza
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Moderator Answer
(gwatson@goldenpaints.com)
Hello Aliza,
We have also seen this issue over the years, especially with blends containing Titanium White. We do not fully understand what, when or why it is happening, but it does seem to have to do with the absorbency of the surface and the thickness of the application. Additions of different mediums also seem to impact the color and whether it changes upon drying. And as you mention, whites containing Zinc Oxide seem to change less.
It could indicate a migration of the titanium white pigment or a shifting of oil content in the film. If the oil were being drawn into the underlying layers at different rates due to film thickness, absorbency etc, it might change the refractive index at the surface and make the color read darker or more saturated. Thinner films can tend to dry darker. Likewise, in thicker applications the oil content at the surface may be more stable, creating little to no color change. Zinc oxide additions may be stabilizing the oil, allowing less migration and/or color change.
We have talked with artists with a history of using blends containing zinc oxide, then switched to ones that are made with Titanium White only. After they switched, they experienced a strange darkening in random patterns across the works they had never seen before. When they switched back, the dark patches no longer appeared. So, we have reason to believe zinc oxide can play a role, but it is certainly not the only factor.
We have seen the issue with the same color layered on non-absorbent surfaces and in single layer applications over surfaces with different areas of absorbency. It is very varied. Unfortunately, we do not have a clear path forward to recommend where this issue does not arise, but it is worth testing medium additions into the paint and monitoring the absorbency of the surface and application techniques. Mixing tints with whites containing zinc may also help, but then you have the issues of embrittlement that come with zinc… It is a perplexing and interesting phenomenon that merits further research!
Let us know how it goes and we will be sure to publish our finding in Justpaint.org once we have some insights to share.
Greg at GOLDEN
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