An Insect Treatment
This article originally appeared in Exchange,
a newsletter published by the Wisconsin Historical
Society. (Volume 29, Number
3, Summer 1987) It is the 29th in
a series of articles titled Conservation
Corner.
The series features information about
maintaining an adequate environment for the
storage and exhibition of historical collections,
employing proper collection care techniques,
and recording and cataloging historical collections.
It was written by Tom McKay, retired local
history coordinator for the Wisconsin Historical
Society.
At one time or another, almost every local
historical society has found items in its collection
that have been infested with insects. To silverfish,
beetles, moths and many other varieties of
insects, a museum, archives or library offers
a veritable smorgasbord of cloth, leather,
wood, paper and glue. Treating insect-infested
items through fumigation has required the use
of chemicals hazardous to people and, sometimes,
to artifacts as well. As a further complication,
chemical treatments that eradicate adult insects
do not kill the larvae and pupae in all cases.
Because of these concerns, fumigation often
dictates the use, and expense, of professional
exterminators. By using a recently developed
technique of freezing insect infected artifacts,
local historical societies now can avoid the
problem associated with fumigation for many
items.
The insects that attack historical collections
cannot withstand temperatures of 0 degrees
Fahrenheit and below. An ordinary household
freezer can reach these temperature extremes.
By observing appropriate precautions, historical
societies can use freezing temperatures to
eliminate insect infestations, including their
larvae and pupae. The important precautions
are treating only items that can be safely
subjected to freezing temperatures and carefully
preparing those items to be placed in a freezer.
Colder temperatures cause most materials to
contract. The flexible fibers of cloth, leather,
paper, fur and hides allow these materials
to contract under freezing conditions without
structural damage. Most items made of these
organic materials can be placed in a freezer
to eliminate insects. However, cautions still
exist. Some items made of these materials have
decoration painted or glued on the surface.
Paint and glue are different substances that
will contract at different rates than the organic
surfaces to which they adhere. Colder temperatures
make both paint and glue more brittle. Freezing,
which contracts and embrittles paint or glue,
could cause fragile painted decoration to flake
off or weak glue spots to give way. Examine
any decorated item carefully before deciding
whether to treat insect infestations through
freezing. Unlike other substances, water expands
as it freezes. Moisture in items that have
sustained water damage frequently helps attract
insects. If insect infested materials are damp
from water damage, allow them to dry out before
treating them in a freezer.
While insects will infest wood, artifacts
made of wood or that include wood have the
greatest limitation on the use of the freezing
technique. Wood appears as a component of many
composite objects that also have parts made
of metal, glass, paper, leather, or several
different varieties of wood. Each of the materials
in a composite object will contract due to
cold at a different rate. These different rates
of contraction can cause structural damage
to an artifact, and the freezing technique
should not be used on composite objects. Wooden
objects may also have flaking paint layers,
weak glue joints or loose veneer. Stress from
freezing temperatures could cause further damage.
Only simple wooden objects in good condition
such as canoe paddles, potato mashers or rafting
pins should be treated for insects by freezing.
Artifacts that can be treated for insect infestation by freezing require careful preparation before placement in the freezer to prevent damage from water condensation or the formation of frost. Begin by loosely wrapping the object in two layers of acid-free tissue paper. Place the wrapped object in a plastic bag and force as much air out of the bag as possible without damaging the object inside. Forcing out the air reduces the total volume of water vapor that will be trapped inside and decreases the possibility of condensation within the bag. As an extra precaution, do not bag and freeze artifacts on hot, humid days. The amount of water vapor in the air on such days increases the possibility of moisture condensation within the bag. After forcing out the air, close the bag tightly with a knot or a twist tie. The danger of condensation within the bag will be very low. Should any film of moisture form on the inside surface of the plastic, the layers of acid-free tissue will catch and absorb it.
Once the artifact has been properly bagged, place it immediately into a freezer. Set the freezer to its lowest setting. The artifact should stay in the freezer for 48 hours. At the end of that period, move the bagged object to a refrigerator. Remember to support the artifact from below and handle it with extra care. Everything becomes more brittle at extremely low temperatures. After 24 hours in the refrigerator, remove the bagged artifact and allow it to come to room temperature. The artifact must remain in the tightly closed bag until it regains room temperature. Moisture will form on the outside of the bag, but it will not affect the artifact if the bag remains closed. By limiting the use of this technique to appropriate artifacts and following the bagging and freezing instructions exactly, this simple procedure can eliminate insects, larvae, and pupae from valuable historical materials. |
