Wooden facades without coatings have become popular in Norway, especially for large buildings like multi-story houses (Hundhausen, 2013). To obtain a quick and even greying, a one-off treatment with iron (II) sulfate is often applied. Iron (II) sulfate, also called iron vitriol, has been used as colorant for centuries in many applications, e.g., to manufacture iron gall ink (e.g. Krekel, 1999, Klöckl, 2015) and not least to stain wood (e.g. Canevari et al., 2016, Edlund et al., 1997). The latter is commonly ascribed to a reaction with phenolic wood extractives, particularly hydrolyzable tannins (Sandermann and Lüthgens, 1953). The Fe2+-ion reacts with gallic acid to ferrous gallate, which subsequently oxidizes to a dark ferric pyrogallate complex (Krekel, 1999). This does however not sufficiently explain vitriol’s pronounced staining effect on wood species containing only marginal amounts of phenolic extractives. Moreover, little is known about the influence of the wooden substrate and light conditions on the color development of vitriol-treated facades. Against this background, we investigated the influence of wood extractives, light and 9 different wooden substrates treated with vitriol on the staining effect.
Keywords: iron sulfate, wood staining, wood extractives
Authors
Ulrich Hundhausen
Treteknisk (Norw. Inst. of Wood Technology), Oslo, Norway
Maik Slabohm
Florian Gschweidl
Ronald Schwarzenbrunner
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