isolating coat over egg tempera grisailleApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2020-02-18 15:25:41 ...
Most recent comment 2020-02-19 09:00:07
I have serious doubts
about what kind of isolating coat would be most appropriate for me.
I'm looking for a varnish to seal egg tempera that is also
compatible with a final varnish, which will go over the last layer of
As the isolating coat penetrates over the tempera, it
becomes part of it. I would like to know, according to your criteria,
which combination of varnishes I could use.
Here is the
structure of my paintings:
Egg tempera underpainting in grey
values. This layer is extremely matt, due to the fact that I thin the
ET with a lot of water. Then I apply combined oil glazes and
intensify the lights with white tempera grassa (highlights). Finally
I finish the painting with oil paint.
I have tried Paraloid
B72 (15%) by Kremer and it is completely transparent. The problem is
the brushability. So I only manage to apply it in small areas. It is
impossible to give a uniform layer to the whole painting and I prefer
not to spray it.
I have tried Gamvar (Gamblin) as well. The
brushability is great, kind of gelatinous. But even after drying it
is still a bit yellowish or dark. And I am not sure if it is
compatible with ET.
One last question. In the following link
it says that if adding UV light stabilizers to the varnish it should
be added to both layers (isolating coat and final varnish), what do
Thanks a lot in advance and best regards.
Answers and Comments
The recommendation from the article on the Natural Pigments web site and what I originally provided here are for an isolating varnish and a final picture varnish over egg tempera painting—not between egg tempera and oil painting layers:
All varnishes work differently on casein, distemper, egg tempera, gouache, and watercolor paintings than on acrylic and oil paint because the varnish is absorbed by the paint and/or paper, becoming an integral part of the picture that could cause discoloration as the varnish ages. In addition, varnishes on these paintings such as egg tempera cannot be removed because they become an integral part of the paint layer.
If egg tempera is to be varnished, an isolating coat is necessary to allow the application of a final picture varnish that can be later removed once it becomes dirty, yellow and brittle.
UV hindered amine light stabilizers can extend the life of both a final picture varnish and isolating varnish, so it is desirable to have it in both varnishes.
The main problem with most varnishes on egg tempera is haze forming under the varnish after it is applied to the painting. We believe that varnishes made with polar solvents are less susceptible to forming haze than those with aliphatic and aromatic (non-polar) solvents. We are presently testing such varnishes on egg tempera paintings.
I do not recommend applying any resinous varnish over an egg tempera painting to isolate it from oil paint, because of its solubility should the oil painting be varnished or cleaned using solvents after it is completed. The recommendation above is solely for an egg tempera painting.
I do not recommend resinous coatings under oil paint for the
reason George mentions but also because the resin can become incorporated into
the superimposed oil paint if it is soluble in mineral spirits. The presence of
a UV scavenger could make this even more problematic as if this were to become
incorporated into the oil paint it could severely inhibit the oxidation and
curing of the paint film.
The way around that is to use a varnish that is not soluble
in the same sort of solvents that are used to thin paint (shellac, B-72, etc)
The problem here is that the isolating coat could still be attached by slovents
used during later conservation treatments. It is not uncommon for alcohols and
acetone to be apart of a cleaning mixture. If you decide to do something like
this make sure to record your practice and materials on the back of the artwork
(see our “Resources” Section)
Sorry that was not of more help.
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