Dear MITRA moderators and community,
First of all, thank you so much for your time and expertise. I really appreciate this valuable resource that you are providing.
My question is about relative humidity, and its potential impact on artwork, particularly on oil paintings. I have read your very informative pdf about artwork storage and whatever else I could find here or elsewhere about the issue, but did not see specific information as to what specifically constitutes “wide swings” or fast changes in RH. Would this be something really quite drastic, such as leaping from 35% to 85% in 30 minutes, or does the phrase refer to more numerically subtle conditions, such as 55% to 65% within 24 hours?
Since late May or early June, I’ve been experiencing humidity issues in my rented studio space that I definitely did not have last summer. I have a combined thermometer/hygrometer there as well as in my home studio. At the start of this, I was experiencing high humidity levels in the rented space of 70-75%, and even discovered some brown drips down one of my interior walls!
My landlord has been very responsive, and after fixing an air duct leak that had caused the brown condensation drips, he purchased a small dehumidifier for me to use. I know to avoid “wide swings” or fast changes in humidity, so hopefully I stepped it down slowly enough at first. While I was initially pleased that the dehumidifier unit has manual settings and three fan speeds to facilitate a slow change, unfortunately it just can’t maintain a steady humidity — I am usually still getting 10 or more percentage point swing each day. The daily temperature has remainded constant — 70-72F.
The supportive landlord is now making several changes and improvements to the property, including sealing my two exterior brick walls from the outside, as well as underneath my concrete floor from the basement, which will all hopefully contribute to a more managed interior climate. In the meantime, is a daily swing of 10% considered a “wide, fast spread”? My target is to get it down to 50% RH, but after a spike, I am setting it for 60 then 55 in an attempt to walk it slowly back down again.
I wonder if bringing the oil paintings back to my admittedly overcrowded home studio would be a better temporary storage solution until the landlord gets this under better control. I do have client and curator studio visits in the rental space, so moving the oils isn’t the ideal solution for other reasons, but the longevity of my work is of greater importance to me. The paintings that are hung on the two exterior brick walls (unavoidable since it’s not a cavernous space) have blueboard backings. The only deformations I have found are on some studies done on small, flat panels that have no cradling. (I have already spoken with the Ampersand representative on how to handle that issue.) I have both oils on stretched linen and oils on cradled Gessobord panel in the space, both finished and framed, as well as in progress. I also have works on paper (framed and unframed) and framed photography in the space.
I appreciate any further specifics you can provide on what exactly a “wide, fast” humidity spread would be in 70-72F, and whether it would be better to safely pack up the paintings and bring them home for now.
Thanks again!
PS — I should clarify that the minor deformations to the small, flat panels are some bowing issues that, thankfully, can be remedied.
Thanks so much for your quick reply, Brian! Much appreciated. Your answer regarding the 10% RH spread really put my mind at ease. As you say, we can only do our best.
I do have a few follow-up questions:
1. What would you define as a “fast” RH change?
2. Since my landlord is planning to seal the brick, would that mitigate your concerns about hanging paintings on those two exterior walls? Otherwise, my ideas include rotating the work around, or hanging framed work in other media on those walls — though it really looks quite nice the way it is currently installed. :o)
3. Since historically, it has taken me a bit longer to execute an oil than it might a faster painter, when you say “older oil paintings” here, I am wondering how you would categorize 2007? Those are the oldest oils I currently have hanging on those exterior walls.
4. I do have a couple of paintings that were exposed to subpar climate conditions elsewhere, so the stretcher bars for these linen canvases got just a little twisted. If you lay them upside down on a flat surface (while protecting the painting side), they easily come back into square. Is it a reasonable approach to carefully put triangular braces of masonite (or another material) on the backs in the corners to hold the paintings square once more?
5. During periods of low humidity in the winter, what is the best way to safely raise the RH of a studio space?
Thank you again so much for your time and information! I really appreciate it.
At Winterthur, our goal is to control rh swings to no more than 10% in 24 hours. This is pretty standard practice these days, although some museums still aim for 5% in 24 hours. In the summer we maintain our environment between 40 and 65% and in the winter 30 – 55%. Again this range is a bit broader than some are currently accepting, 35 – 55 or 40 – 60 is pretty standard.
Hanging anything on an exterior wall can be problematic but in my house, I do it all the time. We also do it at Winterthur. One thing to watch for is significant differences in interior and exterior temperature and rh. The result can be condensation on the back of a frame. If you can find a way to mount the piece of the exterior wall with a spacer between it and the wall (allowing some airflow) you may mitigate this risk.
To be honest, most museums now aim for a range of about 10% so you should be fine. I worry more about putting the paintings on exterior walls but understand that this cannot be avoided in your case. We aim for best practices knowing that we may not always achieve them to the letter. While it is not an excuse and should not be relied on to avoid damage, new oil paintings are generally much more flexible than older oil paintings and should be able to withstand a bit more movement than can those that are older and more brittle.
I do not have exact numbers for you but I have asked a conservator who specializes in preventive conservation to comment.
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