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Voodoo darkening - titanium white.
A few months ago I complained about light sections going dark when I turned my back on them. I discussed it in this thread: https://forum.drawmixpaint.com/discussion/14473/disappearing-highlights-and-light-brushmarks#latest
Well, it turns out I wasn't crazy. It's been christened Voodood Darkening (I think by Julie Beck who put the test together). It felt like voodoo. It turns out in thin layers titanium white tends to go a little darker as it dries. Since I tend paint in thin layers until the end, no wonder I was struggling. This video shows that this person learnt it isn't just happening in organic pigments such as umbers - but in phthalo blue and cad red deep. I can add other blues such as Cobalt to that list based on my experience. The cause isn't understood.
The remedy appears to be thicker layers. A little bodied oil such as stand oil can also address it. However, considering the 'fat over lean' rule - which is really about painting thinner layers over a layer that hasn't fully cured - it might be something we put up at times with in early stages. Then really lay down those highlights and light sections with some generous paint.
Comments
There are two processes at work here. As you add solvent and/or medium the refractive index goes up making the paint brighter and glossier. Then as the paint dries it becomes more transparent, allowing more of the toned canvas to show through the TW, also as it dries the surface becomes more mat and duller in appearance with a lower refractive index.
Denis
TW out of the tube is 50% linseed medium already looking bright and glossy. Darkening as it dries, shrinks, becomes translucent, shows canvas toning and mattes, dispersing the light to look duller.
Denis
You could oil out and then wipe off any excess so that there is just enough oil in place to remove the sinking in (Perhaps with walnut/safflower oil?)
If you like a gloss finish then a gloss varnish will also restore the true values.
Not really in a position to advise about your seven year old work. But, using quality paint in an impasto style suggests there will be no problems.
Denis
I would think my conclusion is self evident. Fresh, fat oil paint is bright and glossy. Dry oil paint is dull, flat, shrunken and more transparent. The behaviour of light dispersion and refraction is beyond debate. Human perception of colour is profoundly influenced by this chemistry and physics.
I look forward to Natural Pigments proving me wrong.
Denis
@Abstraction, What a fascinating problem. I am sorry to read that you are dealing with it – as it is definitely weird! A question: just how thin do you apply your PW6? I paint pretty thin and have not noticed this PW6 drying noticeably darker. What do you add to your tubed PW6 to modify it for application? What is the brand? Is the painting you are experiencing this with the big family portrait with the complicated ground chemistry?
I think that this is a real problem with real causes yet to be determined. What Julie Beck demonstrated on her video seems to be different than the “Hess’ Paint Defects” because of the large time difference in when the problem becomes noticeable: Julie Beck – fast; Hess- slow.
The Julie Beck Videos: I have watched the video of Julie Beck which you linked for us, and I have some very provisional observations. I need to think about this more, but so far:
- Julie Beck says that painting thin over a white background “should” dry lighter because the thin paint will be transparent and let the white background show.
My observation: well, maybe, sometimes. It depends on a few factors she doesn’t get into, but rather glosses over: 1. The pigment of the paint will be some specific degree of semi-transparency or opaqueness. 2. Just how dimensionally thin the paint is – and if this paint layer has been diluted with solvent. Not every pigment in oil will have the same degree of “transparency” as she suggests. Her logic on this is based on a faulty assumption of how the paint will interact visually with the white ground. I disagree with her that the pink and light blue paint should allow the white background to show through a little. The pink and light blue paint were mixed from red and white, and blue and white. These are not semi-transparent pigments.
- She says that a matte finish from sinking in should cause a dark color to appear lighter when dry.
My observation: 1. Not all dark colors sink in. Not all dark colors will appear lighter when dry. I try very hard, and generally succeed, to paint in such a way that the colors don’t cure lighter, darker, or less saturated, compared to when they are fresh.
Her use of the term organic for classes of paint confuses me, as different painters use the term organic in different ways. This makes it difficult for me to follow her conjecture on how the organic pigments, as a class of paint, react.
My oil paint shifts value and saturation a very little bit when dried. This holds true for ALL colors because nothing appears as fresh and vibrant as fresh, wet, uncured oil paint. But, for me, this value shift is really small, maybe less than ¼ of a step in a 10 step value scale. The value is a little lighter after the paint is set-up. The saturation shift is also very small – I don’t know how to quantify it as I don’t use Munsell calibrations. But for both value and saturation, the changes are so small that I don’t even adjust the new, fresh paint to accommodate this.
Without more specific information about the brand, the medium, the ground, how thick the paint layer it, etc., one can only note that it is a weird problem. I think it is some combination of all these factors.
I have never experienced this in 40-50 years of painting. But, as you know Abstraction, I paint on a completely sized substrate, use no ground with super-absorbent calcium (or else cover it up with a layer of PW1) and do not put on multiple layers of ground, don’t dilute the paint with a solvent, and usually add some walnut oil to retard set-up or Liquin to speed up set-up of the paint. The visual effects of Liquin are similar to stand oil, helping keep the saturation and value mostly unchanging. I also have started using my own mix of 50/50 PW1 and PW6 that I tube and use for the white paint anytime I use white. I find this is easier to keep a consistent white temperature paint. Also, I never paint on a toned surface. I like a white surface – the lighter the better.
Please keep us posted on this as it could help lots of painters.
This might be useful:
https://justpaint.org/oiling-out-of-dead-colors-in-oil-paintings-3/
"A third cause needs to be mentioned, which functions independently of a grounds’ particular absorbency; namely film thickness. For many paints, it turns out this alone is enough to cause a matte appearance to develop, as you can see in the following examples."
As paint polymerises it heats up, this exothermic behaviour is seen in two part resins as they cure and more dramatically in oily rags as they self combust. So, here is another phenomenon that May account for, or at least be partly responsible for, Abstraction’s White shift. The phenomenon is called Thermochromism. That is the material changes colour along with temperature.
Denis
I have never used Langridge paint, but have read outstanding recommendations about it.
ps - I used titanium-zinc white for decades with no problem at all. I am not arguing that the zinc oxide problem does not exist, just that it is not universal and it probably has other factors involved. You are painting on a hard substrate, not canvas, so no ongoing expansion and contraction forces.
The fact that you aren't seeing that on these areas that's darkened when dry suggests that indeed something else is going on..