Egg Tempera and CrackingApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2017-08-15 16:50:47 ...
Most recent comment 2017-08-25 14:34:21
This question is a bit complicated, so please bear with me. I have a fellow tempera painter who's experiencing cracking in the uppermost layers of her paintings. It starts out as very faint, fine lines that gradually increase with successive paint layers; the lines grow and evolve into fine "craquelure", and eventually tiny bits of paint flake off (within a few weeks of application).
Over the years I've heard from a handful of other tempera painters who've seen similar cracking, often (tho' not always) reported in areas of tianium white. In general cracking (or craquelure) in tempera is rare, but with this most recent instance I'm recogninzing it as a problem for some painters and trying to understand it better. I've come up with 5 reasons why cracking may appear in tempera paint:
1. Excess binder. Too much yolk can create stresses as the protein molecules shrink with water evaporation.
2. Too thick a layer of paint. Tempera initially dries through relatively rapid evaporation of its water content, so if too dense a layer is applied it can crack as it shrinks (akin to a dried-out lake bed).
3. Adding too much water to tempered paint. Once the paint is properly "tempered" it's possible to thin it significantly with water. However with TOO much water at some point the various components of the paint become so attenuated that it can create a weak paint film.
4. Over saturating underlying paint layers with water. Research I've read on the effects of various solvents (both spirit and water) on egg tempera indicates that they can induce swelling in the paint films. If a curing paint film is compelled to repeatedly expand and shrink, this stress can weaken the bonds being formed in the polymerization process and create cracks (at least this is how I understand it; I'm not sure about this one... By the way, none of the other reasons I suggest for cracking apply to the painter with the current craquelure problem; however she really saturates her surface with watery tempera paint, so much that the ground stays cool when her paint layeras are dry to the touch, suggesting there is residual mositure within - this is why I suspect this reason for her cracking problem, but I'm not sure).
5. Stresses in the ground and/or support. Cracks in the gesso and/or movement in the panel can telegraph up through paint layers.
My questions to the forum are:
1. Has anyone else seen cracking in egg tempera paint layers?
2. What do you think of the above reasons? Do they make sense?
3. Are their other potential causes of cracking?
Thanks, Koo Schadler
Answers and Comments
Hi Koo....honestly the most common factor that is tied with cracking in egg tempera paintings is number 4. Movement (even slight movement) of the panel support will obviously lead to cracks and/or microfissures in the ground which can then migrate up through the paint layers. Unfortunately if there are already micro-cracks in the gesso ground before you paint on top you might not be able to tell until you start painting (until the surface is wet). There are certainly other possible factors of course (some of which you listed)....your comment about titanium white is interesting however. I am unaware of this issue with egg tempera and titanium white so will do a bit of digging on the conservation side of things....
In my experience, almost all instances of cracking that I
have observed in my own work as well as that of my student’s projects appear to
have resulted from substrate movement, improper ground formulation, underbound
paint, or too thick applications of the egg tempera paint. I have neither experienced
nor read about any issues of cracking in tempera caused by titanium white.
be fair, as almost all of my tempera experience has been in service of
reconstructing older methods as reconstructions, and I almost solely use lead
white except for very short demonstrations and one-day workshops.
I do not,
however, recommend the use of lead white for artistic tempera painting. It does not offer
the same benefits to the paint film in egg as it does in oil and the toxicity
and expense is not justified. Tempera also does not completely coat
and isolate the pigment like in oil and there is the remote chance of darkening
of the lead white (really, quite remote unless you live in a very polluted environment).
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