Hello George,
Thanks for the kind words... :-) Are you referring to the
yellowing/darkening of the Linseed oil during the cure cycle?
The yellowing of linseed oil is generally thought to be caused when
conjugated unsaturated hydroperoxides are converted into conjugated
unsaturated ketones. These unsaturated ketones can produce long-chain
coloured polyenes. Additionally, if 1,4 diketones are formed during the
drying, enol tautomers can react with trace amounts of atmospheric
ammonia. This produces a substituted pyrrole, which can be converted into a
coloured product by oxidation, or by condensation in the presence of formic
acid.
Coloured metal siccatives also play a role in the discoloration and/or
yellowing of linseed oil. To alleviate the yellowing, saturated aliphatic
aldehydes may be added to the oil by some manufacturers. The composition of
manufactured BLO can vary from manufacturer to manufacturer. The area where
the plant grew also plays a part in the specific composition of the base
Linseed oil.
My UV inhibitor experiments are centred on the use of Transparent Titanium
Dioxide (TTD's) and Hindered Amine Light Stabilisers (HALS), in conjunction
with various finishes, including oils. Each of these brings a unique level
of protection to the finish, forestalling colour changes and the degradation
of the film finish. Since the composition of the base oil can have marked
differences, depending on the area in which it grew, I limited the in
initial experiments to one manufacturers brand to limit the variables. Using
the knowledge gained from that series of experiments, I expanded the test to
include commonly available oils.
My testing in this area has spanned several years and has provided a new
understanding of the effect of UV on surface films, as well as the ultimate
mechanisms of attack from UV on the surface film itself. There are ways to
limit, or forestall the degradation of the surface film. There are also
measures that can be implemented to reduce the attendant colour changes
caused by some film finishes. However, it must be understood that not all
colour changes are caused by UV. Other mechanisms can also play a role in
colour change, some of these we can exert control over through various
measures.
I hope to be able to publish the results of my experiments with UV
inhibitors later this year. It may be difficult getting a magazine to
publish it though, as to explain the overall problem and the control
measures necessary, requires a thorough discussion of the mechanisms of
attack, and the measures required to control it. Take care and all the best
to you and yours!
--
Better Woodturning and Finishing Through Chemistry...
Steven D. Russell
Eurowood Werks Woodturning Studio
The Woodlands, Texas
Machinery, Tool and Product Testing for the Woodworking and Woodturning
Industries
³Woodturning with Steven D. Russell² Volume #1 CD ROM * Available
Volume #2 CD ROM/DVD Video * Available Soon
On 8/21/04 5:34 AM, in article
, "George Saridakis"
wrote:
Hi Steven,
I use Tried and True polymerized linseed oil which is supposed to have no
solvents or driers. I use a UV light booth to accelerate the drying and
find that the color change is what I would expect if I left the wood in
direct sunlight for a period of time.
Any thoughts on whether or not your experiments with UV inhibitors might
prevent the "normal" change I am seeing?
ps - glad to have you back!
George
"Steven D. Russell" wrote in message
...
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.
--
Better Woodturning and Finishing Through Chemistry...
Steven D. Russell
Eurowood Werks Woodturning Studio
The Woodlands, Texas
Machinery, Tool and Product Testing for the Woodworking and Woodturning
Industries
³Woodturning with Steven D. Russell² Volume #1 CD ROM * Available
Volume #2 CD ROM/DVD Video * Available Soon
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.)