6 Wood Discoloration

128 6 Wood Discoloration
window construction, water is taken up, distributes in the wood and cannot
evaporate through the coat layer. Fungi start growing and their mycelia, spore
masses or perithecia (Fig. 6.3E) cause the paint layer to flake off with further
moisture increase (Sell 1968). Hyphae of A. pullulans were able to grow
through alkyd paints (Sharpe and Dickinson 1992). Colonization of painted
wood by blue-stain fungi was treated by Bardage (1997). Tertiary blue-stain
fungi do not originate from infected stems or lumber, but are new infections.
Colonized wood shows excessive uptake of solutions, so that spot-shaped
color differences develop after painting, similarly like at the excessive uptake
caused by bacteria. The isolate A. pullulans P 268 is test fungus in the standard
EN 152.
Air-borne blue stain means the spread of blue-stain fungi by wind or rain,
insect blue stain is due to fungi, which are associated with bark beetles (Solheim
1992).
There are different results in view of blue staining of wood that derives from
forest dieback sites. Practical observations and fungal isolations (Schmidt
1985) showed that wood from polluted forest sites was more stained than
that from healthy forests. Laboratory experiments however did not show these
differences (Liese 1986; Saur et al. 1986). Klepzig et al. (1996) found different
interactions of ecologically similar saprogenic fungi with healthy and
abiotically stressed trees. Regarding the storage of spruce, pine and beech
stems (v. Aufseß 1986; Göttsche-Kühn and Frühwald 1986; Schmidt et al. 1986;
Schmidt and Wahl 1987; Nimmann and Knigge 1989) the wood from diseased
trees first tended to faster discolorations due to fungal attack. However, after
longer storage no relation was found between the state of health of the
tree and the damage extent during storage. On the contrary, the stems of
healthytreeswereevenmorestronglydiscolored,sincetheirlongerlasting
drying period provided for the fungi a longer time favorable growth
conditions. Stored planks from damaged pine trees were also slightly less
stained than wood from healthy trees (Schumacher and Schulz 1992). Altogether,
there are no results justifying the occasionally used term “damage
wood”.
Incubation of fresh Scots pine sapwood samples with blue-stain fungi increased
wood absorptiveness and the wood may show a greater ability to
impregnation with water-based preservatives (Fojutowski 2005).
Stained wood is used due its color effects by Swedish woodworkers and
was also used to produce attractive violins (Seifert 1999). Corresponding attempts
to stain timber artificially did however not yield regular discoloration
of the samples (Fig. 6.3A). It is possible to remove the stain from the wood
using oxidizing agents such as sodium chlorite or hydrogen peroxide (Seifert
1999).
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