Framing fresh egg tempera paintings behind glass

Hi Zarina,
 
I’m not a trained conservator and can’t speak to the technical definition of efflorescence; but, as an experienced tempera painter, I can explain the common usage of the word as applied to egg tempera.  It refers to two distinct issues:  
 
1.  One is when paint has too much binder (egg yolk) in it; as the paint polymerizes the excess fats get expelled, migrate to the surface, and create a whitish haze or “bloom” on a painting.   This is also known as fatty acid migration (I call it FAM).   I’ve seen FAM on a few students’ works as soon as a couple of months after a painting is complete, but FAM also can happen many years afterwards.  So, given the variable and very long-term time frame in which FAM can occur, I don’t believe if or when you glaze an egg tempera is relevant to this type of “efflorescence”.
 
By the way, if you ever do find FAM on a painting, the whitish fuzz is not harmful but can be unsightly.  It’s easily remedied, just gently brush or wipe it away.  There is some evidence that varnishing suppresses FAM, but I don’t think this is definitive. 
 
2.  The second way I’ve seen “efflorescence” applied to egg tempera is to refer to mold (and sometimes people confuse FAM with mold, or vice versa).   For mold you need spores (which are everywhere), oxygen and water.   The water content in fresh egg tempera paint evaporates out quickly; depending on drying conditions, the paint reaches more or less equilibrium with the relative humidity of the environment it’s in within a few days (or sooner, nearly immediately, in very low RH). 
 
The potential problem is that egg temperas are (a) often on wood-based supports and traditional gesso grounds, both of which are hygroscopic (water loving); and (b) have a very high PVC (pigment volume concentrate), and high PVC creates porous surfaces more open to moisture – these things mean egg temperas are prone to capture and hold onto moisture, which means they are more susceptible to mold, especially under high RH.  The half dozen times I’ve heard from students about a mold problem, it was after a long, rainy stretch of weather.  Because the culprit is the inherent water loving nature of an egg tempera painting- not how long it’s been allowed to cure or polymerize – preventing mold is not dependent on when you frame (since even a well cured egg tempera can mold under high RH).   

To minimize mold it’s important to keep a painting in a stable environment (I believe 45-60 RH is a good range – I’m sure Brian and Kristin know this number); and coat all sides and back of a panel with a “barrier” paint (I use an alkyd, solvent-based house paint).  This last step is often neglected but can make a big difference to how much moisture enters into a painting; and at least you can control this option, whereas you can’t necessarily control the environment in which a painting is kept.  
 
The longer egg tempera paint has polymerized, the more durable it is – so for the first few months extra care should be taken with handling (such as laying a frame against its surface).  But I would say as long as all surfaces feel dry, and the RH isn’t too high, you can frame a tempera within a few days of completing it.

Of course I’d love to get input from a trained conservator too.  

Koo

​One more thing to note – Dr. Joyce Stoner, who’s spent many years conserving egg tempera paintings (specifically Andrew Wyeth’s), suspects there may be a link between humidity and fatty acid efflorescence.  FAM occrus more often in Wyeth’s egg temperas that traveled between his Maine and Pennsylvania studios; so perhaps changes in humidity encourage excess binder to effloresce.  It’s not definitive by any means – but what is certain is that too much moisture and/or dramatic changes in a painting’s moisture content aren’t good! 

​Thank you Koo, as always for your timely and informative answers.  Happily I work in a very dry and stable studio – the only time I have encountered mould (or bloom) was when I was working in a damp stable/studio a few years back and this obviously got into the panels somehow.  Happily, the client liked the effect!  Still, it is reassuring to know that there is no definite reason NOT to frame within 2-3 weeks of completing an ET painting.  Do you, by any chance, ever put an advice note on the back of your paintings advising storage in stable conditions?  ie – avoiding putting paintings on exterior walls or next to kitchens/humid environments?  Zarina