Plastics and condensation

Jerry Shiner <keepsafe [at] interlog__com> writes

>"Breathing" fabrics and "Condensing" plastics- opinions invited.
>A number of people have queried me lately about plastic "causing"
>condensation (apparently this was mentioned again on a recent Martha
>Stewart segment), so I am canvassing the opinions of professional
>conservators about fabrics "breathing", and plastic "causing"
>condensation.

Can we all agree never, ever again to use the term "breathe" until
it is proven beyond doubt that textile fibers have tiny lungs
(perhaps in the amorphous areas)? Instead, "ventilate" perhaps, or
"porous to air and moisture", both rather clumsy. Any other
suggestions?

The best analogy I have heard is the bread bag theory (as yet
unpublished) from paper scientists/conservators here in the
Netherlands.

You know how if you let bagged bread lie in the sun, condensation
will form on the inside of the bag even though the RH has not
changed. This is due to the sudden rise in temperature which forces
the fibers to release the held moisture. The moisture may then, more
or less, be reabsorbed when the heat is lowered. The theory is that
it is this heating moment which causes the most fiber damage (sudden
change in tension). The tentative conclusion is that it is better to
control RH by controlling temperature rather than trying to control
or remove moisture.

CCI are also propagating this idea I think, but I'm not sure: paper
given at 1987 ICOM meeting?

The article by Stephen Hackney, Framing for conservation at the Tate
Gallery, The Conservator, nr. 14, UKIC,1990: is very good. And if
you can read Dutch, de Restaurator, nr. 2, 1995 has several articles
on research into the browning process of passe-partout cardboard
which are very relevant for framed and stored textiles and cellulose
textiles. These articles largely support your understanding that the
more the fabric "breathes", the faster it ages and develops
discoloring. As usual, the outcome depends on the circumstances. I
have always imagined this stress in terms of the fibers frantically
doing those exhausting starjump exercises as the moisture comes and
goes.

As for plastic storage materials and framing (as I understand it),
if the textile and atmosphere is "dry" at the moment of containment,
then the risk of condensation on the surface of the plastic/glass
will be reduced. The inclusion of moisture absorbent materials
(flannel covered acid free card with framing; cellulose fabric or
acid free tissue in package) in the package should reduce the risk
further (so I was taught). But then these absorbent materials will
also release moisture in the case of heat, thus perhaps even
increasing the degree of condensation! Has anyone ever done research
into this? Have I been laboring under a myth?

In general, I think that it is choice between protection from
outside factors or inside factors. It is of great importance to
understand all the processes involved. Each situation will dictate
different priorities and therefore a different set of selection
criteria for the best storage or framing method and materials. One
has to be willing and able to approach each new situation as unique.
This is of course more difficult and time consuming than always
using the same approach.

Jenny Barnett
Andelos Textielrestauratie
Oude Looiersstraat 65-67
1016 VH Amsterdam
Netherlands
+31 20 427 18 27 (phone/fax)


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                  Conservation DistList Instance 14:26
                Distributed: Wednesday, November 8, 2000
                       Message Id: cdl-14-26-005
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