Creating Old School Dark Finishes for Natural Eco-timber

Iron sulphate or vitriol

Iron sulphate has been used for generations as a surface treatment to create the impression of a weathered wooden façade that has turned grey.

Iron sulphate reacts with tannins in wood and causes a chemical colouring on the surface of the timber.

Iron sulphate is generally mixed with water and is a colourless liquid that is painted or sprayed onto the sawn face of new wood or wood previously treated with iron sulphate.

Over time, treatment with an iron sulphate solution turns the timbers surface an attractive and lasting brown-grey to silver-grey colour, depending on the species of timber used. This process should be done before being installed, as this gives better penetration on the tongues and grooves.

One of the benefits of iron sulphate is that it “self-healing”, generally cracks and damage to wood will be naturally resealed by the stain. Iron sulphate is low toxicity and generally does not contain volatile organic compounds (VOC’s).

Ebonisation

Another method to darken wood naturally is ebonisation, which usually involves a chemical reaction between iron oxide and the natural tannins in wood.

This creates a dark black colour in the fibre of the timber, rather than sitting on top of the wood like a stain - resulting in a solid finish where the grain of the wood is not visible through the colour.

Which timbers work well?

Abodo’s Tundra and Vulcan are excellent substrates for iron surface-based treatments.

The strong tannins in Tundra react quickly with the iron forming a dark brown black colour quickly. The reaction with Vulcan is more sedate, with a long lasting deep chocolate brown.

Contact the Abodo team to discuss finish options.