Egg Tempera artists are sometimes told to frame work under glass, to protect the initially vulnerable surface of tempera from scratches. Both tempera’s ground (traditional gesso) and support (wood-based panel) are hygroscopic. Does framing egg tempera under glass protect the work from ambient moisture, or is glazing more likely to trap moisture, potentially leading to mold, delamination, etc.?
Thanks,
Koo Schadler
Thanks for your input, Brian. I am always appreciative when Dr. Stoner chimes in as well. By the way, I coat the back of my panels with alkyd house paint, as a moisture barrier.
Dear Koo, It is a fine idea to put tempera paintings under glass (WITH SEPARATORS so the glass does not touch the tempera surface). Andrew Wyeth sometimes used exposed white gesso as part of his composition, and sadly one of these works was in the home of a heavy smoker, so as you suggest, the hygroscopic gesso absorbed the yellow-brown cigarette tar. Also, as you say, glass prevents scratching, etc. However, it is VERY important that the framing-under-glass package allows for ventilation (as Brian suggests) because if the framed tempera goes through changing temperature and humidity conditions, especially high humidity or condensation, without ventilation, the tempera paint can mold I’ve seen two cases where sealing up with Marvelseal actually caused mold in a painting that had no mold previously–both happened in private homes where the environment fluctuated. Fuzzy gray mold spores are very different in appearance from the natural egg efflorescence powder or sparkles (stearic and palmitic acids) which can be brushed off readily. Putting a painting under glass does not seem to have any impact on whether the egg tempera effloresces. The Wadsworth Atheneum has three Andrew Wyeth temperas; one is under glass, one is not, and one is in a full silica gel climate control framing package. All three apparently effloresce about equally. We think efflorescence is exacerbated by the tempera undergoing changes in humidity when it is being created or is very “young.” Best regards and keep painting your beautiful works. I love seeing them. Joyce Hill Stoner [P.S. please call me “Joyce”!]
Thank you for your submission Comment: Dear Koo, It is a fine idea to put tempera paintings under glass (WITH SEPARATORS so the glass does not touch the tempera surface). Andrew Wyeth sometimes used exposed white gesso as part of his composition, and sadly one of these works was in the home of a heavy smoker, so as you suggest, the hygroscopic gesso absorbed the yellow-brown cigarette tar. Also, as you say, glass prevents scratching, etc. However, it is VERY important that the framing-under-glass package allows for ventilation (as Brian suggests) because if the framed tempera goes through changing temperature and humidity conditions, especially high humidity or condensation, without ventilation, the tempera paint can mold. I’ve seen two cases where sealing up with Marvelseal actually caused mold in a painting that had no mold previously–both happened in private homes where the environment fluctuated. Fuzzy gray mold spores are very different in appearance from the natural egg efflorescence powder or sparkles (stearic and palmitic acids) which can be brushed off readily. Putting a painting under glass does not seem to have any impact on whether the egg tempera effloresces. The Wadsworth Atheneum has three Andrew Wyeth temperas; one is under glass, one is not, and one is in a full silica gel climate control framing package. All three apparently effloresce about equally. We think efflorescence is exacerbated by the tempera undergoing changes in humidity when it is being created or is very “young.” Best regards and keep painting your beautiful works. I love seeing them. Joyce Hill Stoner [P.S. please call me “Joyce”!]
Hi Koo In my opinion, the framing and glazing of recent temperas is mostly to protect from physical damage. There are some interesting issues that do result, such as a build of of fatty acid efflorescence on the inside of the glass. In general, placing a work inside of an environmental envelope like a frame with glazing and a backing board will slow down the change in temperature and relative humidity experience by a painting. However, with canvas paintings that live in a humid environment, we suggest that the backing board be vented to allow air flow and to avoid creating a micro environment which may trap moisture and contribute to mold growth. Whether to vent or not vent a backing board may be less of an issue than with canvas paintings due to the panel support, but I am not positive. At the other extreme, museums that lend Old Master tempera paintings routinely have them sealed into a airtight frame/glazing package, sometimes with special materials that regulate relative humidity. This is mostly done to maintain a “safe and stable” environment during travel to minimize expansion and contraction of the panel due to changes in the environment which could cause possible damage. This is, of course, the extreme and an unlikely scenario for a practicing artist. We have sent an email to Dr. Stoner, again, to get her opinion as she is very experienced with framed contemporary egg tempera paintings. Depending on her answer, I may be able to reach out to preventive conservation, framing and exhibition experts for further clarification.
