Hi Laura,
CHM uses U-Line food grade polyethylene
bags. They are excellent in quality and come in a huge variety of sizes at a
fraction of the cost the ‘archival’ suppliers provide. U-Line will answer
any questions you have about their manufacturing methods or sub-contracted
materials. Bonus: they’ll send samples too. You are wise to ask
questions! From personal experience I always keep in mind that there is no “international
standard” for the term ‘archival’ and any vendor can apply it
any way they see fit.
-Karen
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Karen Kroslowitz, Registrar
v: 650-810-1022
f: 650-810-1055
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From: Marc A Williams
[mailto:[log in to unmask]]
Sent: Monday, May 11, 2009 9:33 AM
Subject: Re: polyethylene
bags--sources and different types
Laura,
First, let me say I am a pragmatist, not an
idealist, at least with respect to conservation. The answer to your
question is it depends, both on the product, as well as what you are using the
bags for. Polyethylene itself is stable and considered appropriate for
conservation use. However, not all polyethylene is made the same way.
Some have additives and is mostly polyethylene, but it is still called
polyethylene. Some have excess ethylene monomer or catalyst that are left
over from the conversion to polyethylene. How much of this exists, who
knows. I personally doubt that the archival suppliers have any better
handle on this than anyone else.
So, my general rule (of course subject to
inaccuracy) is that if something is food grade - it is suitable for food that
ends up in our bodies, it is OK for museum collections. This is not
perfect, as evidenced by the recent controversy over water and drink
bottles that are made of polystyrene and polycarbonate, and may be OK for short
term use, but can be dangerous if re-used over and over. I have always
felt it was OK to use food-grade polyethylene bags for collections,
particularly for those institutions who want to get the most bang for the
buck. I'm sure others may disagree, but we certainly can't be testing
every bag we use for a bad batch or other inappropriate manufacturing
techniques. At some point, we have to put our faith in something, and I
think that companies that produce a product that could make people sick
and result in huge lawsuits have an incentive to be pretty careful in their
quality control, at least compared to companies that make archival products
which have very little risk of resulting in lawsuits.
These same considerations also apply to
"ethafoam," which is itself made from polyethylene. If the
commercial variety of ethafoam is OK compared to the "archival"
variety, then the commercial bags should also be OK also. As for the
U-Line bags, the description of "100% virgin, high clarity polyethylene
film" would suggest that further investigation is needed.
Polyethylene generally has a cloudy appearance. In order to produce more
clarity, commonly additives are mixed in. If this is the case, they may
leach out over time, such as the concern with Bisphenol A. If the bags
are 100% polyethylene with no additives, they should be fine. The
phrase "100% virgin, high clarity polyethylene film" can be
interpreted to read that the polyethylene that is present is 100% virgin, but
not necessarily that 100% of everything that is present is polyethylene.
Good luck sleuthing!
Marc
American Conservation Consortium, Ltd.
www.conservator.com
860-386-6058
Marc A. Williams, President
MS in Art Conservation,
Former Chief Wooden Object Conservator, Smithsonian
Institution
Fellow, American Institute for Conservation (AIC)