Safe Materials for Museum Storage Cabinets

      Wood's acidity and release of volatile substances make it a risk to stored artifacts, including paper art work. Here's advice on "art-safe" materials for museum storage or display cabinetry. November 13, 2009

Question
I have a large millwork project for storage of sensitive paper documents. The spec is asking for no (or negligible) pH in the wood product. I was told they have used "aspen" before because of these qualities but I can find no documentation on such that supports such a statement. Do any of you know what wood, or if this wood is available to achieve this criteria? I understand it has low pH, but certainly I need more info. Also, what finish is suitable to remain pH free? I believe they used salts in the past but the company that supplied their existing millwork is gone.

Forum Responses
(Architectural Woodworking Forum)
From contributor J:
There's no such thing as 'pH free.' If you want a wood that's neutral then you want it to have a pH of 7. Lower than 7 and you're talking about acids; higher and you're talking about alkali/bases.



From contributor P:
If you are doing millwork which must really achieve museum-standard archival qualities, you cannot have any wood materials exposed to the interior surface of the cases (if cases are what you are building). I'm the supervisor of a museum woodshop, and we face these problems all the time. Wood of any kind off-gasses acid vapors and other volatiles which, over time build up within a closed case and can cause serious damage to the art objects. There is no finish available which will prevent this. Forget about using things such as Medite, which other fabricators have touted due to their being marketed as "formaldehyde free". Formaldehyde isn't the only problem.

The wood and glues in any wood product create an extremely art-hazardous environment. You have to use some type of vapor barrier on the inside surface of the case to prevent this. Some common materials which have proven effective are high and low pressure laminates, aluminum, and acrylic sheets. We often wrap the interior surface of our cases with a product called Marvel Seal, which is sort of an aluminized plastic sheet. Some people iron this down, but we have found that a much easier method is to use 3M transfer tape to hold it down. If this surface is visible, we cover it with Sintra board, which can be coated with an appropriate paint (we have all of ours tested for off-gassing, and allow it to cure for a month before installation of the art) or fabric, also held down with transfer tape.

Actually, one of the easiest materials to use is melamine board. The melamine surface is an effective vapor barrier, which is why HPL also works. If your client has more forgiving standards, here is a list of woods which are considered low in acidity: parana pine, spruce, poplar, elm, African mahogany, walnut, iroko, ramin, and obeche, in descending order of acidity.



From contributor C:
Unless you are marketing yourself as someone who specializes in cabinetry for museums, I'd recommend having the architect or other overseeing authority specify materials. As soon as you provide a product that will purportedly live up to their requirements based on your recommendation you are on the hook for the performance of the materials.


From Gene Wengert, forum technical advisor:
All wood has an acidic pH. A measurement technique is given in wood and cellulose science by A.J. Stamm (1964 publication, so check your library).



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