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Subject: Yellowing polyethylene bags containing Pacific Silvercloth

Yellowing polyethylene bags containing Pacific Silvercloth

From: M. Susan Barger <msusanbarger<-a>
Date: Sunday, August 10, 2014
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. ...

Silvercloth works because it is impregnated with fine particulate
silver.  Since you are not seeing tarnish on your objects, the
Silvercloth is working.  Indeed, the Silvercloth manufacturers claim
that the efficacy of the cloth is not diminished by time because
there is a sufficient quantity of available silver to tarnish in the
cloth, in lieu of your silver objects.  Fine particulate silver
(originally called Carey Lea silver and, now referred to as
nanoparticulate silver) has peculiar properties: It is a good
biocide.  It can be very mobile and can migrate from one place to
another under suitable conditions.  And, of interest here, Carey Lea
silver can appear in a variety of colors depending upon its particle
size.  However, the most common color is yellow.  Photographers know
it as the yellow filter layer used in color films.  Given, your
description, I suspect that you are seeing a slight silver migration
into your PE bags and that the yellow you see is from that silver.
Interesting--you could check this by analyzing the bag for the
presence of silver, although it would take very little silver to
produce a yellow color.

M. Susan Barger, PhD
3 Moya Lane
Santa Fe, NM 87508

                  Conservation DistList Instance 28:11
                  Distributed: Friday, August 15, 2014
                       Message Id: cdl-28-11-001
Received on Sunday, 10 August, 2014

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