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Subject: Mold


From: Per Cullhed <Per.Cullhed>
Date: Wednesday, June 3, 1998
Mark Vine and Zu-Chun Liao raise the question of a suitable
fungicide for mold in a recent posting on the DistList. If possible,
the objects affected by mold should be moved to conditions that will
not support a continuing mold growth. It is the humidity in the
substrate (in this case the art objects) that is the most important
factor influencing mold growth and the one that also is readily
controllable both for individual treatment and mass-treatment.
Remove the humidity and the mold attack will stop. This general
recommendation can be difficult to realize in climates where the RH
is on a constant high level or in libraries or archives with a
complicated stacks or ventilation systems. William A. Chamberlains
article "Fungus in the Library" in Library and Archival Security Vol
4(4) 1982 describes very well how difficult it can be to combat mold
even in an environment where the RH was considered "safe" The
crucial point is that overall RH measurements will not tell the
whole truth as long as humidity levels in an individual book is too
high, but if this humidity level (of the substrate) is kept to safe
levels mold cannot grow.

After stabilising the humidity of the object it is possible to clean
off spores and remains of hyphae bearing in mind the risks some
species of mold can pose to the health of the conservator. An
analysis of the types of mold is worthwhile considering the health
risks such as Mycosis and allergies. For example the Aspergillus
Fumigatus, grows in temperatures between 37-42 deg. C, (body
temperature), and may cause disease. After the cleaning, which may
involve picking off hyphae with tweezers for works of art on paper
to vacuum-cleaning for example books, the object is returned to the
collection if the RH is considered safe. This treatment should be
sufficient and mold will not reappear if the humidity levels are
kept low.

As to the question of using fungicides to kill the spores and
inhibit mold growth this should not be necessary in a case where
humidity levels can be controlled. Killing mold with poisonous
compounds like ethylene oxide, orthophenylphenol or thymol is like
starting a war that cannot be won in a normal surrounding as new
spores always will be supplied to the objects by air and dust. As
much as 5000-100,000 new spores per square meter will fall down each
hour in our surroundings.

However, there is an important exception to the rule of not using
fungicides, and that is when mold has to be fought because the
objects to be protected for some reason cannot be stabilised to safe
humidity levels before mold will start to grow. In very humid parts
of the world this may be the normal case and fungicides have to be
considered, as well as after a disaster that is too big too handle
swiftly. After the disaster in The Academy of Sciences In St.
Petersburg, the books had to be treated with formalin to inhibit
mold growth.

In treating paper objects there is a fungicide that is seldom
mentioned in the literature, but may have some interesting
properties--Boron. Boron based products are well known inhibitors
for fungal as well as insect attack on wood. The Dry Rot Fungus
(Serpula Lacrymans), a very effective wood destroyer, can be stopped
by treating the wood with Boron based products. One type is inserted
in holes drilled for the purpose, and it protects the wood by Boric
Acid which diffuses into the wood.

In "Report from a conference on Non-Toxic Fumigation  Alternative
Control Techniques for Preserving Cultural/Historic Properties and
Collections" (see the CoOL Mold page
<URL:>) there is mention
of William Robinson's suggestions about the use of Polyborates for
wood protection as well as mold control but no details are given on
the mold inhibiting properties. However, the latter has been tested
for cellulose, in a study from Gothenburg University in Sweden,
where the purpose was to study the effectiveness of Boric salts as a
mold inhibitor for cellulose insulation. This study shows that the
insulation impregnated with Boric salts also inhibits mold growth.
Cellulose insulation has been in use since the 1940's in the USA,
and Boric salts have been added as flame retardants, but they also
protect the cellulose from mold, a fact that should be interesting
for paper conservators. Among the interesting properties of for
example boric acid is its low toxicity.

If we go back to the original question of a suitable fungicide, I
cannot recommend Boron compounds as a generally suitable fungicide.
More testing for efficiency, methods for application, effective
concentrations and compatibility for different materials would be
necessary, but I think it may be worthwhile to consider and further
investigate Boron based products in other contexts than as
protectors for wood. It would be interesting to hear from other
conservators of their experience of Boric compounds as a fungicide.

Per Cullhed
Head of Conservation
Uppsala University Library

                  Conservation DistList Instance 12:1
                 Distributed: Wednesday, June 10, 1998
                        Message Id: cdl-12-1-002
Received on Wednesday, 3 June, 1998

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