Chemical staining

Staining of the wood is sometimes called chemical stain. Ferric sulphate gives the wooden surface a brownish gray to gray after short-term exposure outdoors. The surface is similar to old aged wood and is therefore used to patina of new wood, for example during restorations.

Ferric sulphate can be bought in powder form and mixed with water in suitable proportions. With weaker or more concentrated vitriol solution (also copper sulfate mixed with iron vitriol is present) can quickly find a tone that fairly well in line with aged wood, with the grey color by weathering.

We usually recommend 1/2 kg ferric sulphate to about 10 litres of lukewarm water in the treatment of new wood. It is advised to make trial in advance of treatment, preferably a few months before, because the result can vary depending on the nature of the wood, how long it has been stored and so on. The best results are achieved on the new (raw) lumber. Already after a few hours the surface becomes dark, and after a few months to get a brown-gray to silver-gray color (sometimes grey-green).

Ferric sulphate - old recipe

1/2 kg iron vitriol, 30 g of copper sulfate, 1/2 bag of silver stain in 7-10 gallons of warm water. Feel free to add a little soap or liquid detergent, to get better stains. Iron vitriol gives gray colored, copper sulfate gives brown color and silver beet provides some luster.

10 gallons of water gives weak solution. Sometimes 7 liters suffice. The solution is stressed out with brush or sprayed with a hand sprayer of insect spray. Consumption of the resulting solution is less than a half liter/m2 rough wood.

Treatment with iron vitriol solution gives a coloring of the wood, but no significant protection against biological attack and no moisture protection. In some cases - at particularly vulnerable locations of driving rain — should an iron vitriol treated surface post-processed with pigmented oil. Iron vitriol treatment is often a better and cheaper alternative to gray wood stains. It provides a durable, gray surface, which often is considered to become more beautiful with age.

If you want a darker surface, one can add a pinch of nigrosine in solution. If you want a gray-violet colour surface can first be treated with 10 grams of tannic acid dissolved in 1 litre of water (enough to 6 m2). After drying for 6 hours, the surface can then be treated with iron vitriol solution. This makes the surface dark blue (ink) and eventually blue-grey. A ferric sulphate treated wood exposed outdoors for more than a month is an inappropriate basis for topcoat.

In particular the furniture industry also occurs to some extent with solutions of dyes that can stain the wood more or less deeply. Stained wood surfaces thus become less visually sensitive to scratches and scuffs.

European Wood (in China)
C412, Beijing Lufthansa Center
50 Liangmaqiao Road, Chaoyang District
Beijing, P.R. China 100125
T +86 10 6462 2066, F +86 10 6462 2067
Sino-European Wood Center
Room 202, Engineering Department,
Taoliyuan Hou, Xuhui Campus of Jiaotong University,
No.655 Panyu Road, Xu Hui District, Shanghai