Knottaclu
Well-Known Member
Linseed and walnut oil are 'drying' oils and have similar characteristics.
Linseed oil 'dries' through polymerising and in its 'raw' (untreated) state, is a slow process. Consequently, it is important to wipe off as much as possible after applying a coat to shorten drying time (by reducing volume) and reduce the amount of atmospheric dust etc. that is entrained whilst wet.
True 'boiled' linseed oil is made by heating and/or oxygenating (normally bubbling air through it) raw oil to begin the polymerising process and therefore (often only slightly) shorten the drying time. The end result is thicker than raw oil, building a finish more quickly but potentially not penetrating as far. I'm not aware of a commercially source for this but you can make your own.
The 'boiled' linseed oil found in shops could be more helpfully described as 'modified'. Normally, it will include a solvent additive and metallic driers (various metals in various forms that act as oxidation catalysts) and careful quality control will give a quicker and more reliable drying time. It is thinner than heat/oxygen treated oil and so penetrates better. For these reasons, it is the best variant for most situations.
All variants of linseed oil have relatively poor resistance to surface water and particularly water vapour. They darken noticeably with exposure to UV (I was once brought a linseed finished stock to refinish which had a perfect '7' on one side from sunlight shining through a signpainted shop window) but are forgiving to apply and easy to refinish.
'Raw' Walnut oil dries more quickly (and more thoroughly) than raw linseed, and has a longer shelf life. It is available commercially in a heat treated form which builds finish quicker and dries a little faster, as well as lasting indefinitely. There is also a alkyd blend which is very rare. It has similar characteristics to linseed in respect of water and UV, and in application.
The other widely used 'drying' oil is tung oil. Some commercial preparations described as tung oil are actually either wiping varnishes (mixtures of small quantities of drying oil with varnish) or other oils. Raw tung oil dries faster and harder than either linseed or walnut, and a polymerised version (via heat treatment) is available which builds faster and dries a little quicker. Unlike linseed and walnut, tung oil does create a finish resistant to surface water (but not water vapour) but is more difficult to apply.
Knots
Linseed oil 'dries' through polymerising and in its 'raw' (untreated) state, is a slow process. Consequently, it is important to wipe off as much as possible after applying a coat to shorten drying time (by reducing volume) and reduce the amount of atmospheric dust etc. that is entrained whilst wet.
True 'boiled' linseed oil is made by heating and/or oxygenating (normally bubbling air through it) raw oil to begin the polymerising process and therefore (often only slightly) shorten the drying time. The end result is thicker than raw oil, building a finish more quickly but potentially not penetrating as far. I'm not aware of a commercially source for this but you can make your own.
The 'boiled' linseed oil found in shops could be more helpfully described as 'modified'. Normally, it will include a solvent additive and metallic driers (various metals in various forms that act as oxidation catalysts) and careful quality control will give a quicker and more reliable drying time. It is thinner than heat/oxygen treated oil and so penetrates better. For these reasons, it is the best variant for most situations.
All variants of linseed oil have relatively poor resistance to surface water and particularly water vapour. They darken noticeably with exposure to UV (I was once brought a linseed finished stock to refinish which had a perfect '7' on one side from sunlight shining through a signpainted shop window) but are forgiving to apply and easy to refinish.
'Raw' Walnut oil dries more quickly (and more thoroughly) than raw linseed, and has a longer shelf life. It is available commercially in a heat treated form which builds finish quicker and dries a little faster, as well as lasting indefinitely. There is also a alkyd blend which is very rare. It has similar characteristics to linseed in respect of water and UV, and in application.
The other widely used 'drying' oil is tung oil. Some commercial preparations described as tung oil are actually either wiping varnishes (mixtures of small quantities of drying oil with varnish) or other oils. Raw tung oil dries faster and harder than either linseed or walnut, and a polymerised version (via heat treatment) is available which builds faster and dries a little quicker. Unlike linseed and walnut, tung oil does create a finish resistant to surface water (but not water vapour) but is more difficult to apply.
Knots