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Question asked 2017-06-29 10:42:26 ...
Most recent comment 2017-06-30 07:13:07
Egg Tempera
Flexible Supports
Grounds / Priming
Scientific Analysis
Technical Art History
Yesterday I went to the Boston Museum
of Fine Arts to see the show of Botticelli and his contemporaries. It's a
beautiful collection of work, and I marvel that the museum was able to get 500
year old paintings from Italy to Boston - a real treat. Given that the 15th c. was
a transitional time for paint (egg tempera to oil) I was curious to see
the labeling. Most pieces were simply "tempera on
panel"; several were "tempera on canvas"; a few were either
"tempera and oil" or "oil".
I wish labeling in museums was more
consistent and specific. However I appreciate that museums are
generally challenged by finances, resources, time. My guess is
that different museums have different approaches and philosophies to
analyzing mediums (it's not necessarily every museum's priority); a lender has to accept what the
lendee says about a piece; there is not enough money for conservators
to definitively analyze ever work in a collection; it's
still difficult to say for sure what a 500 year old painting is composed of
(especially if mediums are mixed, i.e. tempera and oil). My questions are...
1. Any other thoughts on way medium labeling can
be vague?
2. Some works (as evidenced
by the brushwork and finish) were clearly egg tempera. Other works looked so rich and painterly it
was hard to believe they were
just tempera; hints of tempera brushstroke were evident, but other
areas were smoothly and thickly painted. Is it possible there’s some oil paint in the mix and the works aren't accurately labeled? Or would the varnish that was apparent on most
of the paintings be sufficient to give these egg temperas
an oil look? Or
maybe it's that the Renaissance masters were capable of a much
greater range of effects in tempera than they’re generally credited with (i.e.
they did more than just hatchstroke, as is often claimed)? I’m trying to better understand what’s going
on in these “quintessentially egg tempera" masterpieces (that, in fact, often
don’t look like “quintessential” egg tempera).
3. A traditional chalk and glue ground
lacks flexibility, and egg tempera paint become brittle with age – so I don’t
understood how a 500 year-old egg tempera survives on canvas (i.e. Botticelli’s
Birth of Venus). Could there be some oil
emulsified into the ground or paint? I
know the Birth of Venus is painted thinly (you can practically see the weave of
the canvas in parts, it seems to me) – would the thinness of the paint layers
be sufficient to deal with the flexibility in canvas? Or are most temperas on canvas backed by a
solid panel (tho’ I don’t think the Birth of Venus is….). In short, how to explain egg tempera on
canvas?
4.
As mentioned, much (most?) of the work appeared varnished. Is there a way to determine which of the
varnishes are original, which added in later centuries? How do conservators address a Renaissance painting that enters their collection and has a varnish?
Thanks for your help in better
understanding this wonderful but complex period in art history.
Koo Schadler
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Moderator Answer
(kdeghetal)
I will do the best I can to weigh in on these rather complicated questions:
- Yes labeling is and will likely remain vague at best. The specifications regarding media are seldomly ever derived from ACTUAL analytical results. In fact I would say that less than 75% of the time is this ever the case. Labels that state "egg and oil," egg with oil additions," etc., etc. are often just arbitrary assignments based on visual assessments made by a curator (and less commonly by a conservator).
- It is often impossible imo to make definitive conclusions regarding binding media based on visual assessment alone. One really needs to have the condition report of the painting in hand and ideally a very thorough analytical report. And even then it can be impossible to know what Botticelli and his workshop truly used. Botticelli's works in particular have likely been restored multiple times over. We could be looking at remnants of unoriginal varnish coatings (as you state) or even unoriginal oil glazes. Or maybe in some cases, we are looking at a passage that might be very well preserved. There are many factors to consider here…
- It is no secret that Botticelli and his workshop pushed tempera to its absolute limit as a medium, producing paintings that rival contemporary works executed in oil that originated north of the Alps. So the Birth of Venus could very well be an example of true tempera grassa. Or the ground may have been carefully prepared in a unique manner. The fact that is in on canvas has and likely always will continue to intrigue. I am not aware of any references citing the traditional mounting of tempera canvas paintings on panel (for great references on the early use of canvas in painting check anything written by Caroline Villers). In fact this would be odd considering the fact that a major reason artists began turning to canvas was because fabric was less expensive than panel, so adding a panel on the back would not be cost effective. But I am not sure cost was an issue for Botticelli. One would have to go digging in the archives for that, in attempt to analyze any extant receipts or written exchanges between the commissioner and his workshop. If this painting has been analyzed recently the results have yet to be published. Yet even if cross-sections are obtained or samples are collected for destructive medium analysis (e.g. GC-MS) I doubt that all of our questions would be adequately answered. It would be wonderful to conduct a technical study of the painting with some top-of-the-line analytical techniques but often funding (as you have already pointed out) is the main hold-up. In Italy this is often the problem combined with a whirlwind of political hoops that one has to jump through in order to carry out a technical study of this magnitude on a painting that may as well be the country's unofficial "banner."
- The question about varnishes is tricky. For this particular painting I will go out on a limb and say that it would be impossible to characterize the original nature of the varnish b/c: a) I doubt much (if anything at all) still remains of the original varnish layer b) our instruments are barely able to accurately characterize some of these ancient varnish recipes (e.g. oil-resin) and c) if it was given a layer of egg "wash" at the end it would be difficult to distinguish such a layer from the thin layers of egg tempera paint. But I could be wrong about all of this….I would need to see cross-sections and to be able to examine the painting using all of the criteria I listed in No. 2. That being said there are rare cases where original varnish layers have been identified. If an original varnish is identified it is often very degraded and leaving it on the surface as is is usually not a desirable option from an aesthetic standpoint. What some conservators have opted to do is to leave a small area of the original varnish intact in a place that is not immediately noticeable such as on the outer edges of the composition, possibly hidden by the frame. But most of the time, tempera paintings from the Renaissance possess multiple layers of unoriginal varnish so the concept of removing them from the surface is not one that is hotly contested. I should state that for gold ground tempera paintings it was generally not typical for artists to varnish the surface of the gilded sections. Portions of tooling/incised work may have been given a tinted varnish but even that was not especially common. But today of course many gold ground paintings are completely covered with a varnish layer. Conservators today do take this into consideration when dealing with gold ground paintings.
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