[Nhcoll-l] Mildew on plastic-covered herbarium specimens

[Hawks, Catharine]

Hi Deb

When and where were the specimens collected? If is very easy to mistake metallic mercury or other dark mercury reaction salts (from prior treatment with mercuric chloride) on sheets for mold/mildew - both can have a grayish-black appearance. Enclosure in a plastic sleeve might trap the vapor and cause it to redeposit on the paper.

Cathy

_______________________________
Catharine Hawks
Conservator
Collections Program-Conservation
MRC 170 Rm M85-J
w 202.633.0835 or 4041  c 703 200 4370 or .202 701 8458  hawksc at si.edu<mailto:hawksc at si.edu>

SMITHSONIAN INSTITUTION
NATIONAL MUSEUM OF NATURAL HISTORY
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From: nhcoll-l-bounces at mailman.yale.edu [mailto:nhcoll-l-bounces at mailman.yale.edu] On Behalf Of Lewis, Deborah A [EEOBS]
Sent: Friday, July 14, 2017 1:34 PM
To: nhcoll-l at mailman.yale.edu; herbaria at nacse.org
Subject: [Nhcoll-l] Mildew on plastic-covered herbarium specimens

Hello, all,
I've just made a disheartening discovery in our herbarium... Some of our specimens of "fluffy"-headed grasses were covered with plastic sheeting (open on at least two sides so that the sheet could be removed for study) during processing for accessioning. I'm not sure of the nature of the plastic, but the mounting paper of some of these specimens shows signs of mildew - aargh! Obviously, this plastic needs to be removed as a first step! But I have some questions beyond that:
1) What more should be done to stop the growth of the mildew (if that is even possible)?
2) Obviously it occurred, at least in part, from trapped humidity. After the plastic is removed, can it spread to adjoining specimens if the RH is at acceptable levels? Could the nature of the plastic itself have contributed to this? I'll check the current RH in the room and in the herbarium cabinet where these were stored, and, although only a "snapshot in time," can send that information to anyone willing to offer some help.
Thanks in advance for any answers and suggestions!
Deb Lewis

Deborah Q. Lewis, Curator
Ada Hayden Herbarium (ISC/IA)
EEOB Department                                 Phone:  (1) 515-294-9499
Iowa State University                           FAX: (1) 515-294-1337
342 Bessey                                              Email: dlewis at iastate.edu<mailto:dlewis at iastate.edu>
2200 Osborn Drive
Ames, IA  50011-4009  (USA)

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