Proceedings e report - Firenze University Press

WOOD SCIENCE FOR CONSERVATION OF CULTURAL HERITAGE
reached but not to be maintained. Smaller test series in the scope of a research project at the University
of Applied Sciences and Arts in Hildesheim achieved the result of a lethal temperature around 35 -
40°C [5]. The treatment with a pulsed microwave system could reduce the lethal temperature even
further down to 25 - 27°C. During both methods of treatment the microwave exposition time was not
longer than 20 mins.
So far the results gained through microwave treatments have shown the possibility to deal with a
method which offers a low lethal temperature, despite known difficulties and risks. According to this it
seemed to be reasonable to confirm these results in the scope of a Master thesis at the University of
Applied Sciences and Arts in Hildesheim [6], readapted to more practical demands with a changed
experimental set-up.
Aim of the experiments
The aim of the experiments was to find a cautious method of treatment with a low lethal temperature.
Low temperatures result in a homogeneous heat distribution, on the surface as in the cross-section,
alter the wood moisture less, cause low vapour pressure, reduce stress for the object and cause less
danger of damage. Furthermore special attention was paid to the following questions:
• How long must the object be treated and how high must the temperature be raised to kill the
mycelia?
• Do different kinds of radiations have different effects, like permanent treatment, interval
treatment or pulsed treatment?
• Are there differences in the lethal temperature depending on the activity of the fungus?
• Does the humidity of the wood have an influence?
2. Experiment
About 75 cultures were cultivated in advance, with mycelia of the dry rot fungus. When they had
grown 1250 small sterilised wooden coniferous blocks were put into the Petri dishes and on the
mycelia. For each type of radiation, test and activity three parallels were prepared. Every parallel
attempt consisted of four samples to assess the disinfection, two samples to check the vitality with
BacLight and growth, and two samples for microscopy and determination of the wood humidity
before and after treatment.
Fig. 1. Microwave system from the Swiss company Service-Partner with all components used in the
experiments: Energy supply unit (A), remote control (B), microwave radiator (C), clock timer (D), frame (E)
When the blocks were colonised and penetrated with mycelia, half of the samples were dried to a
wood humidity around 18% above salt solutions, to get living but inactive mycelia into a passive state.
The second half of the samples with active mycelia and a wood humidity around 80% was directly
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