MITRA Forum Question Details

​I think gamvar has gamsol in it which is an odourless mineral spirit. Could you try to paint over the egg tempera with a clear acrylic isolation coat (as Golden advise for acrylic paintings), and then apply a varnish layer?

I'm a tempera painter, not a conservator –I'll be interested to hear what the conservators have to say.  For now, here are a few thoughts based on many years experience varnishing egg temperas.

Because egg tempera is such a high PVC (pigment volume concentrate) paint, its surface is very porous and absorbent.  Same goes for a traditional gesso ground.  So both are like sponges, and anything you apply sinks in (or, as you aptly say, goes through like a sieve).  

To successfully varnish a tempera, you must first isolate the tempera with a thin layer of a fast-drying coating. You want the layer thin because you want to minimize excessive, unnecessary coatings on a painting; you want it fast-drying so it doesn't have the "chance" to sink in.  Conservators generally recommend Paraloid B72 as an isolator.  It's flexible, non-yellowing, and remains removable by its original solvent as it ages (although removing anything form an irregular, porous, high PVC surface is a challenge. You can basically presume an isolator becomes an integral part of a tempera painting - unless you're Andrew Wyeth or the equivalent - as it would take a lot of time for an experienced conservator to remove).  You can buy B72 in pellet form (I got some from Talas) to dissolve yourself (acetone, ethanol, toluene, xylene) and apply with a sponge brush; or there are some commercial products in spray cans made from B72 (including, last time I checked, Lascaux Spray Varnishes and Krylon Crystal Clear Coating).  Both applications have their challenges; a sponge brush can leave ridges as the isolator quickly dries, spray application can create orange peel – so it's critically important to practice on inconsequential works and get good at applying an isolating layer before doing so on important artwork.

 I've tried other isolators on tempera, including: super blonde shellac, water and solvent based PVAs, Golden GAC 500 & Soft Acrylic Medium (as the other poster suggested), Casein Fixative and Laropal A81.  All worked, all have pros and cons, none is necessarily better than B72 (depends on your goals and preferences) - just want to clarify that there are many options. 

Once the tempera is isolated, you can apply pretty much any varnish you want on top.  

As to the question of bloom, there is more than one kind of efflorescence (mold, salts precipitating out of a pigment, fatty acids as discussed below); essentially anything that comes up and "flowers" onto the surface.  People sometimes talk of a moisture-based bloom in tempera, but I don't think this is correct – there's no place for moisture to get "trapped" in a tempera painting because its porous surface allows for moisture to evaporate out.  

In my experience, under tempering (too little egg yolk in the paint), isn't as common as over tempering (too much egg yolk).  There is a correct ratio of yolk to pigment in egg tempera paint, and more yolk is not beneficial.  On the contrary, excessive yolk can lead to Fatty Acid Migration, a type of efflorescence that can occur in tempera (and occasionally oil) paintings.  If the paint film has too much binder in it, extra lipids migrate to the surface and create a whitish fuzz; it can happen within months to many years after the completion of a painting.  I see examples of FAM fairly consistently, often from painters who apply nourishing layers.  If you are tempering well, nourishing layers are not necessary and potentially problematic – I recommend against them.   

In fact, I'm wondering if the bloom you are seeing might be FAM –perhaps, as the Gamvar sinks into the surface it's helping to "push" out excess lipids?  FAM is believed to be exacerbated by high humidity but not suppressed by low humidity.  It is seemingly less common in small panels, more prevalent in large panels (See Dr. Joyce Stoner, Erasing the Boundary between the Artist and the Conservator, AIC Paintings Specialty Group Postprints, 2000).  Although not a well-understood phenomenon of egg tempera, there is some suspicion that isolators and varnishes suppress FAM in tempera – which would argue against your bloom being FAM.  So I don't know what the bloom is.  This is the point at which we need a conservator to chime in.  

Koo Schadler

To Koo's point, I would expect Gamvar to quickly sink into absorbent egg tempera layers. The other varnishes she mentioned have a higher molecular weight compared to Regal Rez 1094 (the resin in Gamvar), and in turn, will likely result in a more concentrated coating on a porous surface.

Also, per Brian's question – Gamvar Satin or Matte (or any varnish containing matting agents) will result in whitish reside due to the solvent/resin components sinking into absorbent paint layers and leaving the larger matting solids on the surface.

Both Regal Rez 1094 and Laropal A-81 can be purchased in dry form through our Conservation Colors site.  

Kind regards,

Scott Gellatly

Gamblin Artist Colors

​Thank you, Koo, Briand, and Scott!
The gamvar was glossy (not satin or matte), so no chance to leaving the matting agent on the surface.  I suspect it has something to do with what Koo mentioned, that Gamvar pushed up something to the surface, some grayish-whitish film which I was able to rub off with a piece of cloth.  Since it was my first experience with Gamvar, I proceeded to apply several coats of it.  After a week and 7 coats, I had to remove it all as it looked ghastly.  It didn't even look like egg tempera but like something plasticky.  

As I removed Gamvar with Gamsol, it also removed some of the paint film; upon drying, mineral spirits in Gamsol "bleached" the painting.  Not sure I can rescue it...

George O'Hanlon sent me two varnishes from his line, Laropal Isolating varnish and Regalrez Finishing Varnish.  I tested them on some spots, they both sink into the paint film, and as long as they render the tempera water-insoluble, I am fine with it.  But they are not super-strong and do not protect the paint film from abrasions. (I used them on water gilded surfaces and they didn't hold well)

What would you think if I did the following:
Isolating coat with Laropal, and then the finishing coat with Lascaux Gloss Acrylic varnish (waterbased)?  (I have seen people using Lascaux Gloss varnish, it does not look glossy at all, more like egg-shell.)  

Another option (the one I prefer) is to isolate the tempera, then apply a wax medium on top.  Wax mediums are not as protective as, for example, Regalrez - but there is (along with the isolator) some protection, and the finish isn't too glossy or plasticky, more soft and organic-looking, akin to the natural finish of egg tempera. 

You're description of the grey-ish whitish substance that you were able to wipe off sounds like FAM (which, by the way, is the treatment for this efflorescence - you simply, gently wipe if off with a soft rag), but I haven't heard of those circumstances (i.e. that a varnish instigated it). Do the conservators have any thoughts on the possibility of the Gamvar soaking in and pushing out excess lipids?  Is it feasible?  If not FAM, any other thoughts on what the efforescence might be?

As for your colors appearing "bleached out" after cleaning off the Gamvar, not sure what explains that. Is it possible that, as the varnish was dissolved by the application of solvent, and then whatever varnish remained in the porous paint layers re-hardened, it "trapped" some of the exiting fats to create essentially a semi-transparent, white scumble around pigments that lightened them?  Speculation, of course....just trying to understand why the colors now appear bleached.

Be cautious of applying too much strong solvent atop egg tempera.  My understanding is that they can swell and thus potentially stress and weaken the paint film, and draw out plasticizing components, which can lead to embrittlement.  

Koo

​Here is a bit of observation regarding this "bleaching out" after applying Gamvar and even more so after removing it with Gamsol (which is mineral spirits essentially).  I coated the bleached out areas with a somewhat diluted egg emulsion, and the bleaching disappeared.  It is hard to tell what it is.  It could be an optical effect, but it can also be some deposit brought to the surface by mineral spirits.  

More to it, when gamsol made the painted layer to peel off - not everywhere, but where the coat was rather thin.