Egg Tempera Glazing Medium

Question

I have a painter friend who wants to isolate every layer of tempera she applies because she vigorously works each new layer yet doesn’t want to affect underlying ones.  She wants to work in a similar vein to the English painter Nina Murdoch, whose working method is described as egg tempera alternating with varnish layers.  My friend wrote Murdoch to ask what she uses as a varnish but did not get a reply. I’ve read catalogs that describe Murdoch’s work –
https://issuu.com/marlboroughfineart/docs/1561_mfa_nina_murdoch_artwork_issuu
https://issuu.com/marlboroughfineart/docs/murdoch_aw2_issuu
One image shows a very high gloss, saturated surface – so I am puzzled what Murdoch could be using to achieve her working method and high gloss, but which keeps her work in the realm of “Egg Tempera”.  (Of course I realize that artists’ descriptions of their work, catalog captions, even museum labels are not always complete or completely accurate).
The catalog also mentions Murdoch’s favored glazing medium recently went out of production; coincidentally my friend noted Sennelier’s egg tempera glazing medium has been discontinued – could that be Murdoch’s secret formula?  We don’t know. I couldn’t find Sennelier’s glazing medium ingredients but their binding medium is made from egg, oil and gum Arabic.  I would rather such a medium not be described as “Egg Tempera”; I think it would be more clarifying to call it Tempera Grassa or egg/oil emulsion – but I realize I have no say in the matter. 🙂
I’ve wondered how the tubed egg temperas (which are in fact tempera grassas) by Zecchi, Sennelier, Rowney, etc are made – they can’t use a yolk in its entirety as the paint would putrefy. Do you know how they do it?

Back to Murdoch’s work, and my friend who’s trying to understand it; she also prefers the more saturated, rich look of varnished tempera. I have told her that, while alternating multiple layers of ET and some sort of water insoluble isolator is potentially quite problematic, I believe there are reasonably durable ways to isolate a final tempera layer and then varnish it.

Any thoughts on the above are welcome.

Koo Schadler

Brian Baade · Answer

Koo
As usual, your question is multifold and challenging. I can only state my opinions and in some cases can only make guesses with some of my remarks. Unfortunately, anyone can call their medium anything they want and there is nothing that can be done to enforce a rational nomenclature. I hate the use of the term gesso for acrylic dispersion grounds and refuse to use the term for such materials on MITRA. I will, of course, have no effect on the sloppy use of the term. Even manufacturers, who certainly know better, continue to do so because they do not want to confuse their customers.
I am guessing that the artist in question is using washes of egg-oil or even egg-natural resin emulsions between varnish layers. Emulsions of egg and oil or resin still dry to a relatively matte surface in my experience. The fatty component would have to be quite high to retain a strong surface sheen. The addition of gum Arabic to an egg oil emulsion may create a less matte surface as suggested by Sennelier description of the medium. I have a jar of it in my collection of materials, but have never really experimented with the product. The high gloss would suggest that the interlayered varnishes are substantial and likely make up a large portion of the bulk of the paint.
As you suggested, alternating water soluble layers between slick and/or glossy resinous or oil layers is a recipe for future problems. I have been a part of a study of the works of Henry Ossawa Tanner and many of his later works suffer horribly due to an analogous working procedure. His technique is actually very complex and too complicated for the discussion at hand.
I do not know the exact formulations of the egg-oil emulsions sold as egg tempera by a number of manufacturers. I believe that they are a mixture of egg yolk, a drying oil, and a preservative. I will reach out to Sennelier to see if they would like to comment.
Certainly, there are less problematic methods to create a varnished tempera surface. I know that you once used shellac with reasonable results. I would suggest that a coat or two of B-72 (dissolved in a mixture of xylene and ethanol) over the tempera should serve as a good isolating layer and could be removed with toluene or acetone later if this was required. Egg tempera should not be sensitive to acetone like oil films can be. A standard picture varnish could be applied over this layer. Please do tests on mock paintings before using this procedure on your own work. I have used this and poly-vinyl acetate in solution (ethanol) over small tempera paintouts, but never on a fully realized work of contemporary art

Brian Baade · Answer

​Thanks so much Andrew. We would all love to have more info about how you are able to create an egg-oil tempera paint without fear of purtrification.

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Egg Tempera Glazing Medium