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Question asked 2018-01-02 23:10:06 ...
Most recent comment 2018-01-03 20:41:30
I wish to bleach my linseed oils by letting the sun hit them. I was curious to know if i could do this to an already polymerized oil like Stand Oil? If not, I take it a cold press linseed oil is the best to use for starting.
My goal is to have a viscous clear oil which if need be I can then make it more fluid with a clear cold press oil.
I know traditionally artist would wash their cold press oil and then thicken it and bleach it through exposure of the sun. Should I do this? Is my Stand Oil a lost cause then?
Answers and Comments
Factory-prepared stand oil is already highly refined, so I don't think "washing" would yield any improvement. I doubt any discernable "foot" would deposit as with unrefined oil.
I have washed and bleached oils many times in the distant past
but today I am not sure about the value of such a product. As to water washing,
it does remove impurities from cold pressed or unrefined oils but the product
is in no way superior to modern alkali refined oils. In fact, the resultant oil
is very acidic. This may be fine for some purposes, like grinding oil paint,
but there are alkali-refined oils available in a whole range of acidities. The
best of these are going to be superior to anything that can be refined at home.
This is covered more fully in this thread:
Sun bleaching is also less useful than it initially appears.
You can certainly sun bleach oils to absolute water whiteness. The problem is
that there is some color reversion over time. Take a sample of your bleached
oil and keep it in a cabinet for a while and you can see this yourself.
I can see no benefit to bleaching modern stand oil, which tends to
be quite pale and is one of the most durable of the oily paint additives. I am refering to linseed oil heat thickened in a vacuum as oposed to archaic uses of that term.
The one oil processing that does make some sense to me is
sun thickening. The product of this is both partially oxidized and partially
polymerized. It will behave very different from stand oil and will naturally
dry much faster than raw oil or stand oil all without the addition of catalytic
driers. This is not to say that it is superior to stand oil, just that it moves and dries very differently. Additionally, if the sun thickened oil is made with a quality oil (either alkali
refined or sun thickened as you wish) it is a more appropriate paint additive
than boiled oil or blown oil.
No, stand oil probably would contain no foot. Even with
other less pure oils, my experience with washing oils tells me that it is easy
to fool yourself into thinking that you are removing substantial impurities even
when this is not the case. Any actual foot can act as an emulsifier for the oil
and water phases.
Thicker oils readily emulsify in such conditions. I learned this the hard way
when I tried to sun thicken oil above water in a single washing and thickening
process. It worked fine for a while but if I shook the whole after the oil
began to thicken, it was very difficult to separate the two phases. Even
freezing was only partially successful and resulted in a large degree of loss.
This is another reason why it is unwise to try to wash thickened oils like
I feel that there is no benefit to home washing cold pressed
linseed oil to create a water white oil for making your own paint. The results
are unlikely to be superior to a high quality alkali refined oil intended for hand
grinding oil paint. This does not mean that you should not do it. Nor does it
mean that if you do so your work will suffer. All drying oils yellow to some
degree. Some take longer to get there but all will yellow. Purified oils do
seem to yellow less, at least initially. High quality alkali refined oils are
more pure than those refined at home.
My understanding and general sentiment is that you are
better off spending your time on the craft of painting rather than fussing with
purifying your own oils. Some would say that the same could be said of making
one’s own paint. This is partly true, as it is impossible to make a paint
by hand that is as well dispersed and as lean as that made on large-scale
roller mills. However, the ability to control which, if any, amendments are
added and to make a paint with just the right feel can be very useful for some
who really relish in the diverse rheological qualities of different pigments in
oil binder(s). It is also very
interesting to experiment with fresh oil paint free of thixotropic thickeners,
but this would be a waste of time for many painters who want a range of quality
paint that all handle and dry in a similar manner.
A good quality linseed oil for grinding, perhaps an oil of a
lesser acidic number for mediums, stand oil, and perhaps a partially oxidized oil
like homemade sun thickened oil for specific handling properties, should cover
more than enough bases and be perfectly reliable (as long as rational painting
practice is followed).
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