The whole publication in PDF - Culture in Development

0�C within 4 hours and –20�C within 8 hours. The most commonly reported successful treatments have been carried
out at –29�C for a period of 72 hours. It is unknown whether lower temperatures for a shorter time would be equally
effective; there are reports that –20�C for 48 hours has also been used with success. Collections should be slowly
thawed (brought up to 0�C over 8 hours) and brought up to room temperature. The entire process should then be
repeated to insure effectiveness. Objects should remain bagged (some institutions leave them bagged for 6-8 months)
until monitoring in the space indicates that the insect problem has been solved. Detailed documentation of each
phase of treatment should be maintained. Like chemical treatments, freezing provides no residual benefits. If
collections are not returned to a well-maintained storage area, re infestation will almost certainly occur.
Insect pests in museums may be eradicated by freezing as an alternative to the use of fumigants and pesticides.
To avoid damage from the freezing process, specimens (herbarium sp ecimens, dried skins, taxidermy specimens,
mounted insects, skeletons, etc.) must be sealed in polyethylene bags at room temperature, cooled steadily to –20
�C, and held at this temperature for at least 48 hours. The bag must not be opened until the contents have thawed
to room temperature (at least 24 hours). Repeated freeze-thaw cycles are recommended to assure insect eradication.
Freezing to control insect pests in museum specimens will be most effective when it is used as a component of an
integrated pest management program. (Florian, 1990)
7.4.2.2 Heating
Heat can effectively exterminate insects; it has been used widely used in food processing and in the production of
medicine. A temperature of 140 �F for at least one hour will kill most insects. Heat should not be used to eliminate
insects from paper collections, however, because heat of this magnitude greatly accelerates oxidation and paper
ageing. At these temperatures paper will become brittle.
7.4.2.2.1 Thermo Lignum-system
The Thermo Lignum® process eradicates insect pests with warm air and without any chemicals. It is swift and
sympathetic to health and environme nt. Objects of any kind are treated under optimum conditions by means of a
complex, electronically controlled chamber system. Object moisture readings are taken and provide the starting
parameter for the process. B ased on this data all other relevant process factors are calculated and programmed. A
thermal processor unit controls the complete procedure whilst the key parameters in the chamber: temperature,
relative humidity, and object core temperature are logged and displayed by computer.
There is no doubt the system works in killing insects, and may be efficacious in killing some moulds. The
conservator’s fear is the application of high temperatures. The perceived worries are the effect of high temperatures
(above 50�C) causing the following problems: softening of waxes, synthetic adhesives, surface coatings, etc. Other
problems are materials with low glass transition temperatures; direct expansion of brittle materials such as glass;
shrinkage of animal skins in leather-bound books (Child, 1994).
7.4.2.3 Modified Atmospheres With Low-oxygen Or Inert Gases
Modified atmospheres have been used widely in the agricultural and food industries to control insect infestation.
The term refers to several processes: decreased oxygen, increased carbon dioxide, and the use of inert gases,
primarily nitrogen. Cultural institutions over the past 10 years, have undertaken various experiments with modified
atmospheres with generally successful results. Modified atmospheres show great promise, but additional research
is needed to determine optimum exposure times and methods for particular types of insects. There appears to be no
obvious damage to collections, but little research has been done on long-term effects. There is potential danger to
staff from exposure to high levels of carbon dioxide, if that is used, but there are no residual effects on collections.
Modified atmospheres can be applied 1) in a traditional fumigation chamber or a portable fumigation bubble or 2)
in low -permeability plastic bags. With a chamber or a bubble, materials are prepared for treatment (quarantined,
documented, and loaded into the treatment chamber), air is evacuated from the chamber, and carbon dioxide
(generally about 60% concentration) or nitrogen (to achieve an atmosphere of less than 1% oxygen) is introduced.
Once the desired atmospheric concentration is reached, conditions are maintained at a specific temperature and
relative humidity for the required amount of time. Once treatment is finished, the vacuum is released, the carbon
dioxide or nitrogen is removed, the chamber is aerated, and materials are removed to a quarantine area so that the
effectiveness of treatment can be assessed. The process for treating materials in low-permeability plastic bags is
similar, except that materials are sealed in bags with an oxygen scavenger that will reduce the oxygen level in the
enclosure to less than what is needed for insect respiration. In some cases, the bags are purged with nitrogen before
sealing. In the tests cond ucted thus far, a variety of exposure times, temperatures, and relative humidities have been
used. Since requirements for achieving an acceptable kill rate seem to vary according to the type of insect being
exterminated and the type of process being used, there are not yet any generally accepted guidelines for the
application of modified atmospheres. Always contact a preservation professiona l for advice before proceeding with
modified atmosphere treatment.
7.4.2.4 Gamma Radiation
Gamma radiation is used to sterilise cosmetics, food and agricultural products, medical supplies, and hospital and
lab equipment. It poses som e danger to personnel during treatment, but there is no residual radiation in the treated
material. Gamma radiation can be effective against insects, but the minimum lethal dose for various species is still
unknown and is affected by variables such as climate conditions and the nature of the infested material. Most
important, research has shown that gamma radiation may initiate oxidation and cause scission of cellulose
molecules; it has the potential to seriously damage paper-based materials. There is also a cumulative effect from
repeated exposures. As a result, gamma radiation is not recommended. In the Netherlands there is no other option
to treat archive in bulk.
7.4.2.5 Microwaves