Hello Owen,

No doubt dirty conditions in days long past contribute to the colour of
antiques, but the propensity of Linseed oil to darken is well known in
chemistry circles. I know of a few chemists who have spent years trying to
find a way to chemically reverse this problem with Linseed oil. No one has
ever been able to reverse the colour change without damaging the wood, which
is obviously undesirable. Should you find a way, you would no doubt be a
very rich man.

Raw Linseed oil is the raw oil that has been packaged without any additives.
Boiled Linseed Oils are similar, except the boiled version has been altered
through the addition of chemical drying accelerators (solvents and
siccatives/driers) and may also include up to 15% Stand Oil, so the colour
change would be similar, if not more apparent in the boiled version.

Driers are oil soluble metal salts of organic acids. When these driers are
dissolved in aliphatic or aromatic hydrocarbons, they are know as
siccatives. When driers are added to drying oils, they are known as "Boiled
Oils" Siccatives can also cause colour changes, depending on the specific
types used.

--
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Steven D. Russell
Eurowood Werks Woodturning Studio
The Woodlands, Texas

Machinery, Tool and Product Testing for the Woodworking and Woodturning
Industries

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On 8/18/04 9:48 PM, in article
, "Owen Lowe"
wrote:

In article ,
"Steven D. Russell" wrote:

One thing to consider when whipping up a batch of your own oil is that
Linseed Oil and Pure Gum Spirits of Turpentine will alter (darken) the
colour of your wood over time. Linseed oil has a habit of turning very dark
to almost black over long periods of time... Go to any antique store and you
will see this on old pieces finished with Linseed oil. Currently, there is
no way to chemically reverse the colour degradation caused by Linseed oil.

Are you sure this same result would occur with modern boil't linseed oil?

I've heard the argument that the antiques that appear dark may be due to
the much dirtier heating systems of old - oil, coal and wood soot
becoming embedded in the finish. (I do know that raw linseed oil used
outdoors will often host mildew which will turn it very dark- but that's
a different situation.)