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  • Egg Tempera and CrackingApproveRejectUn-ApproveSubscribeUn-Unsubscribe
    Question asked 2017-08-15 16:50:47 ... Most recent comment 2017-08-25 14:34:21
    Egg Tempera
    Question

    ​Hello MITRA,

    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
  • EditDeleteModerator Answer

    ​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....

    Kristin deGhetaldi
    2017-08-16 12:52:34
  • EditDeleteModerator Answer

    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.

    To 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).

    Brian Baade
    2017-08-16 14:00:29
  • ApproveRejectUn-ApproveUser Comment

    Thanks for your replies, Kristin and Brian.  I think the very fine cracking in this student's work is unrelated to the support or ground (I know the panels she's working on, they are good quality; and other students working on the same panels are not getting craquelure).  I think there is something going on with her application of multiple, very watery paint layers, and I'm trying to understand it on a technical level (and hoping it would explain other, similar examples I've heard of over the years).  Whatever is occurring, it's an uncommon problem and there may not be enough cumulative experience or study in egg tempera to answer the question.  But maybe you can find other voices to chime in.  

    I appreciate your thoughts on lead white in egg tempera, Brian - I feel the same and it's good to have corroboration.

    Koo

    2017-08-17 08:30:34
  • ApproveRejectUn-ApproveUser Comment

    ​Koo, As you seem to suggest that this cracking occurred due to paint application irregularities rather than preparation of the support, have you reached any conclusions regarding use of water in the tempered paint? You have prevdiously suggested that once the paint is tempered, the amount of water used should not harm the binding properties of the emulsion. Do you have any further guidelines regarding the technique of laying down initial layers of thin washes to start a painting or in the use of water washes to glaze in color over dried or built up layers? Does this incident suggest caution in the use of too much water especially in early stages of a painting?

    2017-08-19 13:07:11
  • ApproveRejectUn-ApproveUser Comment

    ​I apologize. I did not include my name in the previous comment. This is the first time I have commented on this forum. 

    Jason

    2017-08-19 13:08:52
  • ApproveRejectUn-ApproveUser Comment

    Hi Jason,

    I don't have definitive answers, just observations and thoughts.  I'm continuing to ask around regarding this topic, trying to learn more, but there's not a lot of people working in tempera or looking at specialized topics within it – so I'm lacking facts or examples.  For now, this is what I can tell you: 

    Once you have the proper ratio of yolk to pigment (the paint is correctly tempered) you can, as you note, add considerable amounts of water to thin the paint.  However at some point, with really a LOT of water, the various components of the paint become so separate and attenuated that it's a good idea to add a drop or two more yolk to the mix.  

    When to do this?  I can't say precisely, but with practice you develop a feeling for it; the paint just looks and feels too watery, doesn't quite look or feel like paint.  It's an intuitive sense developed over time.  Stay attentive to your tempering, the quality of your paint, and the quality of the surface you're developing (does it look and feel too dry, chalky, lacking in binder?).  I check my surface regularly by feeling it, and by an occasional gentle polishing with a soft piece of cheesecloth – if I can pull out a subtle shine I'm on the right track.    

    Another consideration: In a very watery paint it's possible for the yolk and pigment to separate out from one another as the paint sits – so it's important to recombine the elements of watered down paint before you dip your brush into it.  It's become a habit for me to always swirl my brush in the paint a few times before loading.

    Regarding your question, I don't think (tho' I'm not sure) this cautions against applying very thin, watery layers to start.  There are many tempera artists who start with very thin paint, so I don't believe it's the problem.

    At this point the possibility I'm most curious/concerned with is the consequences of oversaturating a developing tempera painting with water.  I'm getting an experiential and intuitive sense that repeatedly saturating underlying layers of tempera paint isn't good for the paint layers; that too much water sitting in them weakens them. 

    This doesn't mean don't work with a watery paint.  Just be sure to wipe your brush well before you apply it (as an experienced tempera painter, I'm sure you know what I mean – the paint goes on a bit like dry brush, but doesn't chatter or skip; still flows, but in a controlled manner).  Or, if you do apply puddles of paint (i.e. a petit lac), either do it early in a painting (not on top of dozens of underlying paint layers that are in the process of polymerizing); or apply a wet layer than immediately sop up the excess water before it soaks into the painting (I do this with a kitchen sponge; it can be done without lifting underlying layers, with practice).  And if you are applying a lot of watery layers on top of underlying layers, give the painting time to dry well in between; i.e. if the surface feels dry but is also cool to the touch, you know there's still a lot of residual water in the underlying layers.  Wait for that coolness to dissipate before adding fresh layers. 

    I wish I could be more precise in what to tell you, but I'm still trying to figure out this student's problem, which I have seen only a handful of other times over the years, but is recurrent and is clearly is caused by something.   Any clues as to what that something could be are most welcome!

    Koo

     

    2017-08-25 14:05:49
  • ApproveRejectUn-ApproveUser Comment

    ​Koo, I want to add to this discussion in hopes that other tempera painters will do like-wise. I am still learning and subjects like this are ones I would like to master so that these types of problems do not hinder the creative process. That part is hard enough.

    I am learning that the application of a watery wash (or application of a water-thinned stroke) takes a good bit of practice as to when, where (in the painting), how much, and even what brush to use in order for it to be successful. Some brushes, like a soft, sable filbert can lay down a nice smooth water-thinned stroke if used in a flat technique, but can cut through underlying layers of paint and cause lifting effect if turned on edge as if you were laying down a thin line. A lot of the outcome seems to be dependent on how long the underlying layers have been allowed to dry. 

    And that is my only conclusion after reading this thread. I have found that i need to give my built up layers time to dry adequately before applying any thin watered-down glazing. 

    I am also learning that the type of support I am using seems to effect lifting problems. I have used many hardboard panels for paintings, but am now using birch plywood and finding it a bit tougher. I don't experience pin holes near as often and have not had lifting problems like on hardboard. I sealed the plywood with RSG and it seems to provide a more absorbent surface that allows me to be a bit more aggressive without penalty. I can lay down several water-thinned layers during initial block in without problems that I previously experienced. 

    Thanks for keeping this forum up to date. Certainly Cennini and students must have wrestled with this kind of problem. Did he write about it?

    Jason

    2017-08-25 14:34:21
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