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Question asked 2019-10-22 11:46:42 ...
Most recent comment 2019-10-31 04:26:45
I have a question about varnishes for egg tempera. Until recently, I used boiled linseed oil, but it is a tremendously problematic varnish which changes the nature of painting (lead white becomes transparent, azurite becomes green etc.) So I decided to seek something better. Several substances came to my attention, one of them was GAMVAR. I tested it and got very unpleasant surprise: wherever Gamvar came into contact with egg tempera paint, dreadful white spots appeared. NOTE: those were not "blooming", I'd know the difference. This was some kind of whitish residue that appeared on top of the painted layer, while Gamvar completely sunk into the paint. Under-tempering is not a factor in this, I temper my paint quite well (egg-shell sheen), and apply nourishing layers often. I also know that those whitish spots look exactly like when I had to clean gilded parts with mineral spirits, some of it got onto the paint and bleached it immediately.
My friends who work in oil swear by Gamvar. I decided to persist and varnish the painting I just finished with Gamvar, and even after 6 consecutive coats, there are lots of sinking as if it goes through the paint like through a sieve.
Anybody had experience with this or has other varnishing options for egg tempera? The properties I seek are:
1. Non yellowing
2. Something which would not cause blooming
3. Reasonably strong to protect the painting
Answers and Comments
I actually have little to add to Koo’s response. I have not
varnished many egg tempera paintings that had not already been varnished in the past.
I do have a question about the Gamvar. Was it satin or
matte? The only time that I have encountered a similar effect was when I
applied a varnish containing a matting agent to a very absorbent surface. The
varnish was drawn into the paint leaving some of the matting agent at the
surface. This was very disfiguring.
I will sent this thread to representatives from Gamblin and
a conservator who has more experience with varnish on contemporary egg tempera
I would worry about the adherence of an acrylic dispersion
over a solvent-based isolating varnish. Yes, it is very easy to overdo
Regalrez-based varnishes and create a nail polish-like effect. As Koo
indicated, it is usually best to isolate the paint with a high molecular weight
varnish like B-72 that will not sink too much into the stratigraphy and apply a
thin application of a lower molecular weight varnish like Regalrez or Laropal
A-81 to the top.
As to the Natural Pgments products, I am guessing that
George has his varnishes formulated in solvents that allow for the application
of the Regalrez over the Laropal A-81 without biting into the isolating layer.
It would probably be best to avoid acrylic dispersion coatings directly over egg tempera. The alkaline pH levels in water-based acrylic coatings could potentially have damaging effects on the fatty acid fractions in the egg tempera and the proteins. Although, we have heard repeatedly of artists who have accidentally applied Golden Polymer Varnish (water based with pH level leaning towards the higher end) over their oil paintings, and they looked fine.
We have never seen adhesion failure of acrylic dispersion coatings over mineral spirit based acrylic (MSA Varnish), at least. But because it complicates the layering for possible future conservation treatments, Golden generally does not recommend dispersions over solutions. Better to apply easily removable coatings over less soluble ones.
To err on the safe side a solvent borne acrylic varnish, like Paraloid B72 or MSA/Archival (spray) Varnish would probably be the best isolation varnish, followed by lower molecular weight one, like Laropal or Regalrez. Being able to remove the Regalrez without the acrylic varnish underneath would be a great advantage and if Regalrez does not sink it really creates beautiful finishes. You might also be happy to leave it with the first varnish. You can find tips on manipulating sheens of solvent based varnishes here: Tips and Tricks for Varnishing
I should have been more clear. You are right that there is
no incompatibility of putting an acrylic dispersion over an dried solvent-born
acrylic coating. I do worry about it over the aldehyde resin.
There doesn't seem to much literature on egg tempera and solvent interaction. The most recent study I found is almost 10 years old. P. Cremonesi et al. (https://repository.si.edu/bitstream/handle/10088/20487/09.Casoli.SCMC3.Mecklenburg.Web.pdf) have tested various egg tempera samples: non-polar solvents (iso octane) extracted significantly more material (mainly fatty acids and cholesterol), than polar solvents (water, ethanol, acetone). Water only extracted amino acids from the proteinaceous fraction. Pigmented layers were less prone to FFA leaching than pure medium layers. Most samples remained visually the same after solvet contact.
Seeing that non-polar solvents have such FFA leaching potential it might be saver to varnish tempera paintings with materials which are diluted and remain soluble in polar solvents, e.g. Laropal in alcohol.
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