I would be grateful to see any information your group might have or know of, historical or current, concerning the long standing practice by some artists of framing pastel works in direct contact with the glass – specifically concerning mold / fungus growth.
Of greatest interested would be any documented instances of mold / fungus growth that were known or suspected to have been directly caused by this practice. Also wondering if there have ever been any studies or laboratory testing done to determine the propensity for mold / fungus growth of pastel works in general and particularly those done on any of the current day sanded papers.
Please note that I am not looking for information concerning the alteration or disturbance of the pastel work by the direct contact with the glass as I have been able to test this extensively myself.
Thanks to both of you for your comments and the information provided. If I had to guess I would say that having the glass in contact with the pastel surface – and having the “package” sealed on all edges as is done by quite a few pastel artists these days would tend to actually reduce the instance of mold growth since the amount of humidity that can migrate into the space would be significantly reduced. Ideally one would want to complete the glass package in a low humidity environment one would assume. Another aspect of reducing the chance of mold growth that I have thought about is the fairly waterproof seal that modern sanded papers provide. This combined with the glass creates a very thin corridor that the pastel resides in, sandwiched between a moisture resistant and in the case of the glass a moisture proof barrier. There is a very small amount of air between the water resistant surface of the pastel paper and nothing else in there the glass except the grit of the paper and the pastel particles to be able to absorb moisture, thus not giving mold much to feed on. The less air the better so it seams. I realize that the long standing conventional wisdom over the last several decades is to make sure that there is a gap between the pastel work and the glass but I tend to lean to just the opposite as being a better method all around. I have read about pastels framed this way that were 80 plus years old that came out of the frame in superb condition. I also have heard from other pastel artists who have been framing with the glass in contact with the work for over 30 years and have not seen any issues. Perhaps some day a scientific study will be done on this topic.
I have run a professional picture framing business for well over a quarter century and regularly correspond and converse with conservators. I strongly recommend against glass directly against pastels for all my pastel artists and customers. I’m not sure where this trend started but I can assure you it was not with the conservation community. I believe it started with a pastel workshop leader somewhere who did not know better. Will it work in many cases, yes. Will it fail in many cases, yes. Anecdotal success is not enough. Much like wearing a seatbelt, the question is, do you want to run the risk of being the failure case? I 100% concur with Ms. Ellis and Mr. Phibbs who says “when pastel is framed … it be done with a low or no static glazing material spaced no more than 1/4” in front of the design”—note the critical word “spaced”, that is, an air gap between the glazing and the pastel. Scientific studies have been done and have already spoken. Works on paper should not be in contact with the glazing.
Also this article about framing pastels may be of interest: https://frametek.com/assets/images/articles/FT-Pastel-Article-for-printing-interactive.pdf
In the Nineteenth Century, artist press pastels against the glass in frames and some used loose cotton behind the pastel to maintain the pressure. The cotton was a great addition, since it meant that the pastel that transferred to the glass, did so in an even manner. This meant that when the pastel came out of the frame, its appearance was not really altered, since pastel has so much more pigment than is needed. The cotton may have also served as a climate buffer, moderating the RH behind the glass and lowering the chance that morning sun light could pass through cold glass, without warming it, and warm the moist paper behind the glass, driving enough water out to form condensate on the glass. That case, is the most extreme, but whenever the relative humidity is high enough, mold spores can begin to grow and feed on cellulose and the binder in the pastel, whether it is touching the glass, or not . Thus, contact with the glass may result in the art being exposed to higher RH, when the glass is cold and sun light goes through it, but it seems impossible to conclude that the contact, between pastel and glass, caused the mold to grow, rather one can say that it may have enhanced conditions for growth. What our ancestors got right, with their cotton pressed framing, was a condition in which the pastel (which is hopelessly loose) that came off, did so without pastel coming off the art and settling on another part of the art. That last case presents a real hazard and suggests that when pastel is framed (as it should be to keep dust off) it be done with a low or no static glazing material spaced no more than 1/4″ in front of the design, to keep the kind of static air cushion we see in thermo pane windows.
Thank you, you have raised an intriguing issue. I am not aware of this practice among artists – if anything pastels have traditionally not been framed in direct contact with glass due not only to the increased chance of mold growth, but also to the extreme friability of the pastel medium. I have seen many instances of mold growth in pastels, especially in the darker colors which probably generate more heat as they absorb light (radiant energy). It seems likely that high humidity levels are easily formed in micro-climates between the glass and the pastel layer. The binder in pastels has usually been thought to serve as a nutrient. Glass has usually been used asa glazing material in order to avoid static charge generated by wiping rigid acrylic sheet (Plexiglas). However, now there is a new acrylic glazing product, Tru Vue Optium, that is non-static. Nonetheless, a “breathing space” must always be provided when framing up any works of art on paper. Sanded papers will not contribute to the problem of mold growth in pastels – as long as a space is provided between the medium layer and the glass or non-static acrylic glazing that will serve to dissipate trapped humidity. Hope this help!
The two moderators that have weighed in on this matter ARE well-respected conservators with extensive experience in the field with international reputations. You are welcome to your own opinion of course and free to frame your pastels in any manner you would like but others would be wise to take note of the advice given above.
