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. ...

Although I don't have a definite explanation for the yellowing of
polyethylene bags after contact with Silvercloth, I wish to comment
on Jerry's suggestion for the cause.  Polyethylene does not contain
plasticizers to soften it.  However, PE bags and food wrap grades
contain antioxidants to minimize degradation during processing at
levels of several hundred ppm.  Until around the 1990s, the most
common antioxidant was butylated hydroxytoluene (BHT) but it is no
longer used.  Cotton clothing that had been given an alkaline
finish, packed in polyethylene bags and stored in the dark developed
yellow stains because nitrogen oxide in the air reacted with BHT
especially around openings, perforations and holes in the bag.  More
about this phenomenon can be read in International Fabricare
Institute Bulletin Technical No. 569 available on

    <URL:http://70.88.161.72/ifi/BULLETIN/TOI/Toi569.pdf>

Yvonne Shashoua
Senior Researcher
Conservation and Science
The National Museum of Denmark


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                  Conservation DistList Instance 28:10
                  Distributed: Sunday, August 10, 2014
                       Message Id: cdl-28-10-001
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