Proceedings e report - Firenze University Press

WOOD SCIENCE FOR CONSERVATION OF CULTURAL HERITAGE
Table 3: Colour of Norway spruce wood specimens after exposure to wood decay fungi
for the period between one and eight weeks.
Weeks of
G. trabeum A. vaillantii
exposure L *
a * b * L *
a * b *
0 89.0 2.4 10.4 89.0 2.4 10.4
1 68.6 5.2 13.2 74.9 5.7 13.2
2 64.7 6.1 13.2 68.2 6.6 13.2
4 58.0 6.6 13.7 64.3 7.1 13.2
8 48.2 6.6 12.8 67.8 6.6 13.2
3.2. Blue stain fungi
As expected, exposure of Scots pine wood specimens to blue stain fungi, resulted in considerable
colour changes. The first signs were visible after the second week of exposure. However, colour
changes of specimens exposed to S. pithyophila (ΔE = 18.7) for two weeks, were more prominent than
the ones exposed to A. pullulans (ΔE = 2.6). S. pithyophila remained more active all the time of
exposure. Within time of exposure, the specimens became darker, less reddish and yellowish and more
bluish and greenish (Tab. 4). Maximum colour change was observed after the sixth week at S.
pithyophila and after eight weeks at A. pullulans. The most important reason for observed changes is
melanin excreted by those two staining fungi [3].
Table 4: Colour changes of Scots pine sapwood exposed to blue stain fungi
Weeks of
Sclerophoma pithyophila Aureobasidium pullulans
exposure L* a* b* ΔE L* a* b* ΔE
0 85.1 3.8 13.7 0.0 85.1 3.8 13.7 0.0
2 66.7 3.1 10.7 18.7 82.6 3.8 14.6 2.6
4 63.8 2.6 9.0 21.8 79.7 2.8 12.8 5.6
6 57.5 2.5 7.5 28.3 71.9 3.1 11.3 13.4
8 58.4 2.5 7.7 27.4 70.1 3.0 10.1 15.4
Mass changes of wood specimens exposed to blue stain fungi were insignificant. In none of the cases
mass losses were observed. In contrary, all specimens gain some weight; firstly because specimens
were prior fungal exposure immersed to malt agar suspension, as proposed by EN 152-1 standard [5],
and secondly, as fungi contributes to the mass of the specimens with their biomass and excreted
compounds like melamine. However, changes of mass are relatively small and are always smaller than
1 % (Tab. 5). Those measurements are in line with data of Highley [1].
Table 5: Modulus of Elasticity, mass changes and carbon and nitrogen content in wood after exposure of Scots
pine sapwood to blue stain fungi
Sclerophoma pithyophila Aureobasidium pullulans
Weeks of exposure Δ m (%) Δ MoE (%) C (%) N (%) Δ m (%) Δ MoE (%) C (%) N (%)
0 0.8 1.2 47.63 0.0352 0.8 1.2 47.63 0.0352
2 0.6 2.8 46.33 0.0205 0.2 1.7 47.00 0.0160
4 0.3 3.6 46.55 0.0181 0.0 1.5 47.02 0.0163
6 0.2 2.5 46.48 0.0175 0.1 2.9 45.60 0.0164
8 0.8 2.7 46.27 0.0181 0.8 1.7 45.97 0.0162
Nitrogen content in uninfected pine sapwood was 0.0352%. Immediately after exposure, nitrogen
content dropped significantly to 0.0205% at S. pithyophila and to 0.0160% at A. pullulans and
remained almost constant within time of exposure (Tab. 5). This indicates that blue stain fungi rapidly
consumed nitrogen within the first two weeks of exposure. This nitrogen was translocated from wood
and utilized for fungal growth in wood as well as it in soundings. The remaining nitrogen in wood is
either in biologically unavailable form or it was used for chitin and protein synthesis and is present in
91