Yellowing polyethylene bags containing Pacific Silvercloth

Jakki Godfrey <jakki.godfrey<-a t->brooklynmuseum< . >org> writes

>We have recently had multiple-instances of yellowing of polyethylene
>bags containing silver objects wrapped in Pacific Silvercloth.  The
>objects had been first wrapped in acid-free tissue and then in the
>Silvercloth prior to placing them in the poly bags.  Each instance
>occurred after the objects were packed in this way and crated for
>shipment for outward loan.  No tarnish or other issues were seen on
>the silver objects. Has anyone experienced this before?

At some point in the distant past, I read a report concerning the
localized yellowing of T-shirts stored plastic bags.  After a great
deal of research, the author discovered that the plasticizers used
in the manufacturing of the polyethylene bag had migrated to the
white T shirts during storage.  Small holes in the bag had allowed
in pollutants, which, in turn, had reacted with, and split the
molecules of the plasticizer (BHT?) that had migrated to the
T-shirts.  The split molecules were yellow, thus explaining the
discoloring.

Perhaps your problem is similar--most plastic products include
additives (such as plasticizers) needed for efficient production.  I
suspect that there will be no effect on the materials inside the
bags, especially as you have wisely protected them with two more
layers.

Of course, for me this is another example of unexpected and
surprising behavior in a microclimate.  I should add this example to
the on line course I am teaching in the month of September 2014 on
Museum Microclimates for The Northern States Conservation Center.
For more information please go directly to:

    <URL:http://www.collectioncare.org>

As I remember, the yellowing of the T-shirts was corrected by
exposing the garments to bright sunlight, which restored the
plasticizer molecules to their original form.  Not recommended for
museum objects!

Jerry Shiner
Keepsafe Microclimate Systems
416-703-4696
Skype: jerry.shiner


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                  Conservation DistList Instance 28:9
                 Distributed: Saturday, August 2, 2014
                        Message Id: cdl-28-9-001
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