Exhibition Case Materials

[T. Ashley McGrew]

Manufactured wood products.

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Separating reality from "what everyone knows" can be tough, and in our desire to help our colleagues we can fairly easily end up spreading mis-information.
I am pointing the finger right at my own chest right now.
OK, not actually, because it makes it too difficult to type that way.

Anyway, I remember talking to one of my favorite bosses of all time - Bruce Metro - when I first started working for him more than a few moons ago and telling him that I had recently been made aware of how medex and medite were recently failing Oddy tests.

Now I said this like it was a relevation or something.
Why? Because like everyone else I knew I had been told that this stuff was just the thing for building exhibition cases (which on a certain level is fine of course - with a vapor barrier).
Well his response was a moment of silence and a patient look which then proceeded on to a discussion of why that might be the case.
He pointed out the obvious. For some reason up until then I had just bought the story that I was told.
It has happened before and probably will again.
The story with Medex and Medite II or.... whatever is that may be promoted as "formaldehyde free" really just means that the level used is somewhat less toxic in terms of habitation than living in a 1970s doublewide trailer.

In reality though for the same reasons that exterior grade plywoods are considered superior to interior plywoods for use in the museum environment (the use of Phenolic-formaldehyde glues instead of Urea-formaldehyde glues) Medex and Medite II are indeed somewhat superior to particle board or standard MDF (medium density fiberboard). That is saying something I suppose, but not all that much.
What is true about manufactured wood products that they all share is one thing - they are made of wood -- and wood is intrinsically acidic.

Seal anything up in a closed environment with wood and you are creating a bad situation.
Oh for porcelain maybe it is less of a big deal - for metals or paper - it is kind of a big deal.

The image above shows three metal coupons on a glass fiber backing (makes it easier to photograph) from an Oddy test. From left to right we have copper, silver and lead coupons respectively.
For a material to pass an oddy test the image on the right should look approximately the same as the control image on the left.
The good (and some would say bad) thing about Oddy testing is that you get to (have to) use your own eyes and your own judgement to come up with a result.
The blob on the right where the lead reacted to the acids released by the Medite paints a pretty clear picture in my opinion.
The good thing about Oddy testing is just this - you can see results with your own eyes.
The ultimate conclusion to the discussion is use materials both in exhibition case and in storage that pass Oddy tests or utilize a real functional vapor barrier like marvelseal to eliminate the risks to objects posed by the process of off gassing.

[T. Ashley McGrew]

Just thought I would add something from the listserve

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Yes the consensus still seems to be that the camger product is the sealant the provides the best barrier of any liquid.

That said. it still doesn't eliminate the build up of pollutants in a sealed case over time - it just slows it down.

A judgement call needs to be made about the sensitivity of the objects placed within the a case. Certainly for sensitive objects it is not going to be adequate protection on its own.

A mechanical film barrier is still required to create a real barrier between wood products and sensitive materials.



I know no one wants to hear that - because it is a real pain - but that is just how it stands. When someone makes a coating that will function as a real barrier I am sure that the word will spread like wildfire as this is a real ongoing concern.

In this case I would not ask anyone to believe me - instead here is a quote from Pamela Hatchfield author of the book Pollutants in the Museum Environment.

There are no sealants we know of that will really do a good job over the long term in preventing wood acids and other pollutants from coming out of the wood into the case. It is much preferable to minimize the presence of wood products and sealants/adhesives with volatile components within the case altogether, and sealing wood with a physical barrier such as an aluminum laminate like Marvelseal. We are using a lot of glass, steel, and aluminum inside cases. You can use Dibond or Alucobond – these are aluminum laminated with polyethylene for deck surfaces, and a wood substitute like Renshape for interior construction of the display area, and seal the interior of the base with an aluminum laminate.

Pamela Hatchfield
Robert P. and Carol T. Henderson Head of Objects Conservation
Museum of Fine Arts, Boston


In the message Pamela also mentions a product called Renshape which is essentially the same thing as the one that Robin mentions . It seems like for both products the thinnest it comes in is 1" which is kind of a drag but it is still worth checking out.



Robin did you have any actual prices on your material? That is one thing that I haven't heard yet in the discussion.



Another material that is less expensive and tools like wood it Sintra or Komatex. It is a PVC foam board which freaks some people out because PVC products normally don't - of course neither do most Polyurethane products like Renshape!

In the case of Sintra it has consistently passed Oddy testing at a number of museums including (but not limited to) the Getty Museum and at least one Smithsonian Museum. In fact I have yet to hear of it failing anywhere!

That is kind of interesting only because I have seen polyethylene plastics (a "safe" plastic) fail testing on several occasions.

Anyway that seems to be the scoop on the topic at this point from what I can tell.



Ashley





Dear Exhibition Prep folks,
Can anyone tell me the current preferred sealer for wood if used inside exhibition cases?
We do use Marvel Seal to cover all surfaces that are not visible, or covered in fabric. (Then we have the shiny surface showing through fabric problem).
But for painted risers and interior case decks, are we still in favor of Camger coatings to seal the MDO ply?
Thoughts?

[Keith Bull]

How does the acidity of wheatboard (made of wheat straw) compare with mdf? One manufacturer, Kirei, claims low formaldehyde content and working characteristics similar to mdf. If wheatboard is closer to pH neutral than mdf is, are there reasons -- besides cost, maybe -- not to use it for case interiors?

[T. Ashley McGrew]

I don't know about the Ph of this material and haven't had the opportunity to use it. If it has the right mechanical properties (workability, structural stability, not too heavy etc..) then it could be fine to use for structural components of the case, but unless the material itself has passed Oddy tests at least a couple of times, if it is to be put in proximate to art that is at all sensitive in an enclosed environment it will still need to be separated with a real barrier (Marvelseal, metal, polyester etc...) or ventilated to prevent build up of pollutants over time.
That said, from what I've heard on some of the listserves not all museums maintain this standard of protection at this point. Certainly you can make a case (bad pun) for exceptions to this approach for some materials - lithics or ceramics maybe?
In my experience it is kind of problematic to approach case design piecemeal though. Even in temporary exhibitions it is by no means unheard of for a bit of curatorial waffling to result in objects being swapped out in cases without the opportunity to "re-hab" them. Better to establish basic standards and be consistent it seems to me.

[T. Ashley McGrew]

Metal/Wood Combination made in-house.

Just thought I would post a link to a really nice blog entry done by John Zehren at the Field Museum.
http://fieldmuseum.org/explore/conservation-case-building
I have a couple of questions about some of the details and one of the materials I had trouble locating on line ( Camger Sancure product 118-1) but further on in the article it mentions Camger 1-175 which I have seen referred to from other sources (apparently formerly known as 1-146) commonly as a sealant, but in this article used as a adhesive as well. All told an excellent piece of work I would say. Hope to speak with him sometime soon. One question would be to find out if he has tried the commercially available ply/aluminum combo called NuAlum (http://www.nudo.com/Sign-Panels/Designed-Performance/NuAlum.aspx)
I had heard of a couple of museums that were ordering some but I never got a report on how well it worked out.

T. Ashley

[John Zehren]

Its nice to meet everyone. Ashley is right, about the Camger number. I entered it wrong in the beginning of the article. It is actually 1-175. Here at Field, we have been working hard to get rid of wood inside cases, and in reality, there isn't any way I've come across to de-acidify wood products. I had high hopes for an oven baking process I came across in Quebec, but it failed Oddy. The processes I've outlined in my Article make it possible to build cases cost effectively, with simple tooling. Furthermore, the same laminate on board can be used for making interior case furniture. The trick is to make a sealed shape, this time with the laminate outwards. It is problematic though, in terms of securing these shapes without penetrating the aluminum laminate. The real issue is the seams. We have not established how vulnerable the joints are over long periods of time (3 to 10 years). We don't know if Camger becomes brittle and vulnerable, or loses integrity in terms of porosity, and at what rate over time. Camger should not ultimately be trusted till confirmed, however, we have used the product to lake around our joints. This varies from a sealing application, in that it greatly reduces the area from which the product is exposed to the interior, and most likely is a much greater thickness or concentration, through which the acid must travel. We have high hopes it will increase the long term effectiveness. I would put forth we start viewing the product differently, and try to couple its use with engineering physical mechanical advantages in our building, like I've discussed it the paper. In the mean time, I agree with Pamela's assessment we are better served looking to metals, DiBond or acrylic to build interior furniture. Unfortunately these materials require higher skill levels, better equipment and ultimately a higher price tag.

[T. Ashley McGrew]

Just thought that to be fair handed I should include an image that doesn't create the appearance that Medite is the only "wolf in sheeps clothing" when it comes to this category of products. Here is an image of Oddy test coupons that resulted from testing of Medex which is the material that was always recommended early in my career as being "safe" for enclosure with artifacts.You can see that the silver and copper coupons are relatively intact but predicably the lead coupons has been seriously degraded. I hate to say it but it just isn't always easy to do the right thing.
1288

[Exhibitek]

Just thought that to be fair handed I should include an image that doesn't create the appearance that Medite is the only "wolf in sheeps clothing" when it comes to this category of products. Here is an image of Oddy test coupons that resulted from testing of Medex which is the material that was always recommended early in my career as being "safe" for enclosure with artifacts.You can see that the silver and copper coupons are relatively intact but predicably the lead coupons has been seriously degraded. I hate to say it but it just isn't always easy to do the right thing.
http://www.paccin.org/attachment.php?attachmentid=1288&stc=1Just wondering where we are currently on this subject of 'safe' substrates for case construction; anything new in the last 3 years?

[T. Ashley McGrew]

The most recent discussion I had was at AIC in Montreal earlier this month. A material mentioned that I had purchased samples of but never really figured out how to use is HDPE board from King plastics. It is basically the material that is used for plastic cutting boards. It is on my list to check out in the near future. Sintra (the real thing not generic substitutions) seems to keep passing Oddy tests along with Komacel (same thing but comes in 3/4" thicknesses). Renshape is still a viable option too as I understand. In other words nothing revolutionary that I have heard of.

[Robbain]

If I could revive this thread, I know the case manufacturers, (like CaseWerks) are using Forex for in-case furniture, but I've had difficulty finding a US supplier- all of their web-presence seems to be overseas. It's my understanding that Forex can be used in display cases without MarvelSeal, and I've got a lot of new cases to outfit in the coming year, so ANYTHING approved by conservation that would allow me to skip wrapping everything twice (MarvelSeal + linen) would really cut down on labor. Does anyone here use Forex and get it in the US?

[T. Ashley McGrew]

Based on what I can tell, Forex is a version of several products available here in the States. The most well known brand - that is also used as a generic term for this type of material - is called Sintra. That generic term can be a real problem in that not all rigid PVC foam boards pass Oddy tests making them unsuitable for use in display cases.
Interestingly the fact that a PVC product seems to consistently pass testing is just maddening to many people including a bunch of conservators I have encountered. Despite this skepticism Sintra has been in use (passing repeated Oddy testing) for at least 15 years now at the Getty Museum and is used by any number of other major museums as well.
Although it does not fit into the world-view of some folks where simple solutions are supposed to make our lives easier - an approach that goes something like "PVC bad - PE (Polyethylene) Good" I always try to remind people that perhaps the most consistently tested and recommended plastic for use with collections - Polyethylene - frequently fails Oddy testing. The gold standard of foams for the last 30 years - Ethafoam brand PE foam - has widely failed oddy tests during two periods that I am aware of and many, many other PE products - foam, film and sheet fail testing everyday.
By the way controversy erupted in 2014 an part of 2015 in the form of a widespread rumor that Sintra was failing Oddy testing. I could never confirm the source of the rumor but it was revealed at the Lunder Center conference "Conservation and Exhibition Planning: Materials Testing for Design, Display, and Packing" November 19-20 2015 that some if not all of the failed tests were the result of distributors substituting similar looking products made by different manufacturers. Anyway Sintra can be purchased by the same kind of sources that you find mentioned on the Forex website - usually sign making suppliers and such. It cuts and screws much like light weight wood product only without grain. It takes paint well. It’s main drawback is that it is less rigid than ply or MDF and my require extra bracing to avoid sagging when used for decking. Good luck!

[Robbain]

Thats great! It's funny, I didn't even consider Sintra I suppose because I only ever see it in the 1/8" - 1/4" range, and I'm looking for deck construction thicknesses, but I see now that it's available in 19mm. Now I'll just have to go through our conservation dept. for approval...

[essay]

A mechanical film barrier is still required to create a real barrier between wood products and sensitive materials.