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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,
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I haven't heard of the term Voodoo Darkening. It probably had a grassroots invention in an art school. However I have encountered the wet bleaching titanium effect and it is most apparent with a painting medium or a very oil rich vehicle paint. Upon drying the paint has a slightly darker tone, making wet on dry tonal matching difficult.
Unless the zinc white is mixed with a good portion of stand oil it can dry quite brittle. Getting ever more brittle over the years. I myself avoid it completely. Also different whites have slightly different color shifts in mixtures you might find matching difficult in getting exactly the same color. In your case I'd use the same paint with perhaps less or a different medium.
Fellow artist, Marc.
Could you share some pictures of the lighter and darker patches?
I'm not familiar with the term coined but can investigate. Do they all become uniform after a good day of sunlight exposure? Is it a darker warm yellowish tint?
Is it glossier and matter on the same patches? Because they can appear lighter when they're less glossy. Do they become uniform when you wet them both with some pure medium?
Apologies for the delayed reply and thank you for writing back to my question! In the attached photo you will see two sets of arrows. The first set points to a grey-green silhouette of a flower and a grey-green stem, which are the exact same paint mixture, but dried to different values.
The second set of arrows point toward a circling grey-blue vine, which is painted with the same mixture, but dried with darker and lighter and patches throughout the shape. Gamblin described Voodoo Darkening as a phenomenon where the Titanium White paint particles shift up or down within the drying paint film.
The lighter areas are not "sunken-in" and applying medium does not correct the issue, and they don't have a yellower tint or different sheen. It's just a value difference.
Things got slightly better after a few days of drying in sunlight but have not corrected. I repainted part of the piece with colors that I remixed, using a 50/50 ratio of Titanium and Zinc White this time, and things seem to be drying much more evenly.
Ultimately, I guess the question is, do Titanium particles commonly move within a mixture? If so, is this phenomenon more likely when layering or when using an oil-rich medium (Gamblin Solvent-Free Medium in this case).
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
The same happened to me! It's been twice I tried to fix it. It was a a mix of a very light blue with a lot of titanium white and ultramarine blue and phthalo blue. Perfect match, than dries darker.
I don’t usually use zinc, but in that case I would try it to fix it.
Thus I was wondering what is the ratio of zinc to titanium you would recommend for that particular case, or what is the ratio the artists who seemed to have fixed the problem used? A 1/4 zinc to 3/4 titanium ratio?
Julie Beck has a couple of videos on youtube about this 'voodoo darkening':
I wonder if using Zinc Sulfide instead of Zinc Oxide or Titanium White would help?