The options for treating wood are many and depend on the final use of the wooden object. It is worth reflecting on what happens to wood if it is not treated. In the outdoors, natural weathering of untreated wood will lead to a change of colour, usually to a silvery grey, and the slow erosion of the surface through wind and dust abrasion and frost/thaw. The constant change in moisture content during the seasons will cause checking and splits that will enlarge over time. Eventually wood rotting fungus will lead to the wood decaying awayIndoors my washing up brush is a good case study on the effects of constant drying and wetting on untreated wood. Over time the surface of the wood has darkened and greyed. The texture has become furry as the end fibres of the wood have lifted above the surface. Fibres will break off to be constantly replaced by newly lifting fibres.
Treatment of wood seeks to avoid these effects. Paints, lacquers or resins can form a hard physical barrier to air and moisture, but if the protection fails it can let in moisture behind the surface, leading to future trouble. Oil based treatments offer an alternative approach, soaking into the wood and protecting from the inside rather than just the surface. In order to be effective the oil treatment needs to set or harden. A mineral based oil may protect wood, but if it essentially stays liquid and can be washed out of the wood or remain a sticky surface attracting dust and dirt. Fortunately many natural vegetable oils, known as drying oils undergo a process of oxidation to harden. This allows the oil to soak into the wood and form a hard matrix. If the wooden object is being used as a kitchen utensil the oil can be washed out, especially by detergents, but of course the piece can be reoiled. An oil treatment can also help to strengthen spalted wood. No oil treatment will easily withstand the high temperatures of a dishwasher.
To treat a piece with oil may need successive treatments to get the best penetration. It is good fun to use your fingers to get the oil into the wood, helped by your body heat. After the second or third treatment any excess oil should be wiped off and then the piece left for 3 to 4 months to allow the oxidation process to take place.
Grapeseed Oil is now my finishing oil of choice, given that is presents no food allergy problems and leaves less colour in the wood than either walnut or linseed oil. It can be found in the specialist oils section of a supermarket.
Food grade walnut oil will oxidise over several months to provide a superb finish. However there may be a problem for people with nut allergies. It is usually available next to the olive oils in the supermarket
Raw linseed oil; The problem with raw linseed oil is the possibility of mistaking it with boiled linseed oil as this contains heavy metals to speed up curing, boiled linseed oil should never be used for kitchen implements. Indeed it’s best to source food grade linseed oil rather than the DIY store material. Food grade linseed oil may also be labelled as flaxseed oil and sold by agricultural and feed merchants as animal feed supplement or for humans in health food shops. Raw linseed oil tends to leave a more distinctive yellow colour than walnut oil.
CAUTION If rags containing drying oils are left in the air they can spontaneously combust. as the oil oxidises and generates heat. Please dispose of such rags carefully.
This spoon has been carved from willow, a very light coloured wood. The linseed oil finish has given it a distinctive yellow hue
A spoon carved by Wille Sundqvist being treated with ‘Linolja’, Swedish for linseed oil