Storing photographic materials

Maria Karen Sigurdardottir <mks [at] rvk__is> writes

>Can somebody give me a information about which material is better
>polyethylene or polypropylene as a storage pages for photographic
>materials?

Both low-density polyethylene and (cast) polypropylene have a
potential problem with slip-agent coming out at a faster rate than
intended. Both of these plastics use <1% of things like stearamide
and oleamide to prevent the plastic film from sticking in the
fabrication machines (which would be a disaster.) If too much has
been slip-agent has been added it will tend to come out as a cloudy
white bloom. The two waxes as inert with regard to photographs, but
it still means that you're getting a waxy coating.

Biaxially-oriented polypropylene doesn't require slip-agents, but is
very expensive since it must be handled like polyester (using
something like ultrasonic welding.) Henry Wilhelm has been pushing
high-density polyethylene (hdpe) since it apparently also doesn't
use slip agents. However, hdpe is translucent rather than
transparent. (Produce bags at the grocery store are ldpe while
larger grocery bags (as in "paper or plastic?" are hdpe.)

Please note that ANSI and ISO no longer accept cellulose acetate as
an acceptable plastic for sleeves. (We do need to reword the ISO
document though since it currently implies that CA is okay.) It
makes no sense to put photographs into sleeves that will eventually
shrink, embrittle, and release acetic acid.

Every material has its pros and cons though. Polyester, which most
people consider to be "the" plastic to use has several disadvantages
as well (for example.) It has a high static coefficient this makes
it unsuitable for anything with a flaking or friable medium or
binder. (I've even seen it lift a whole gelatin dry plate emulsion
off during a workshop.) It also has a fairly sharp edge making it
more prone to causing abrasion than other plastics. Thirdly, it is
one of the smoothest plastics making it more of a risk for causing
ferrotyping in high humidity environments. You'll have to decide
which plastic is most suitable for your needs based on properties.
Good luck,

Douglas Nishimura
Research Scientist
Image Permanence Institute

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                  Conservation DistList Instance 13:30
               Distributed: Wednesday, November 17, 1999
                       Message Id: cdl-13-30-001
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