I was putting some boiled linseed oil on a new jig when I slopped a little
on my table saw. I also slopped some on my pants, but it'll probably wash
out. Anyway, a thought occured to me. I wonder how this would work to
protect cast iron from rusting? I normally use paste wax, but maybe
linseed oil would last longer. Any thoughts?
Spray'n'wash stain stick* works greatly for removing oils from cloth. But ya hafta
lay it in a bit thickly. Not the liquid spray type and not any kind of "shout it out".
On the machine, consider camelia oil.
On Tue, 9 Nov 2004 13:53:29 -0700, "Charles Spitzer"
If it's boiled linseed, then it will indeed polymerize. However not
all of it does so, and there will still be oxidation going on. Most
commercial BLO's are also somewhat acidic anyway (which is why some
peopel re-boil them with limestone chips to neutralised them).
Plain vegetable oils oxidise on exposure to the air and will cause
acid corrosion problems on steels. There are a few that don't
(camellia oil is pretty resistant to this), depending on the fats in
On Wed, 10 Nov 2004 16:21:33 GMT, email@example.com (Lawrence
"Polymerisation" isn't really a description the process, so much as
the end result. There are several ways for an oil or resin to do
this, but it's reasonable to describe them all as a polymerisation --
it's not just the simple long-chain polymers like the reaction of
ethylene to polyethylene.
In linseed oils, the amount of the oil that polymerises varies
depending on the coating thickness and elapsed time. Raw linseed oil
takes a week to air-dry, but not more than about 30% of it will have
dried and little more does so in the future - several years later it
still might not have reached the state that a boiled oil does. Boiled
oils dry in around "a day". The rate of drying varies with
temperature. Rate also varies with humidity, but this depends on the
type of metallic drier used. Lead-dried oils dry faster in high
humidity, manganese dried oils dry slower, or stop altogether at
around 80% RH. A modern linseed oil finish may be simply unusable in
an English winter.
The amount of oil that is polymerised in a "dried" oil varies with
time, but mainly with coating thickness. As is well-known, an
over-thick coating "doesn't dry". In fact it does, it dries as quickly
as a thin coating, but the point at which it stops polymerising is
less. The surface layer might polymerise, but beneath this is a layer
of oil that stopped at around 50% - now unworkable and unremovable,
but still mechanically weak. If the process merely _slowed_, it would
be a lot easier to repair such finishes, we could just wait for them.
As it is, even patience won't help us much.
A worst case for oil coating might be the making of oilcloth, where a
fairly deep penetration of oil needs to be dried. This is one reason
for sizing the cloth before oiling it - if you oil raw cloth it's too
difficult to avoid oiling an over-deep layer that then refuses to dry
in its lower depths. In a good oilcloth, 80% of the oil has dried
after a few weeks and a "finished" cloth, 10% might dry over the next
summer, and 10% never dries, remaining as a plasticiser ("never" means
the useful lifetime of the cloth - after a century or two it does dry,
and the now-brittle cloth will crack). Modern linseed with cobalt
driers tend to dry more thoroughly than this, leading to a brittle
Iron compounds work as a drier for linseed, in that they cause it to
dry more quickly than a raw oil. However they also _prevent_ full
polymerisation of the oil. Even boiling your oil in an iron pot is
enough to cause trouble with this and may lead to an oilcloth with a
permanently sticky finish. Iron pigments have traditionally been
added cold to finished oils, before coating the oilcloth. As well as a
pigment, this may also have an effect in preserving the plasticiser
content long-term. Being added cold, they have no effect on the oil as
it dries immmediately in the couple of days after coating.
If you can find a copy, a useful text here is Leighou's "Chemistry of
Engineering Materials" and the chapter on organic protective coatings.
It's old enough (1942) that linseed oil is still a major economic
material for paint and varnish making.
So is vulcanised rubber a polymer ? Some sources claim that it's
only polymerisation if you're making a long chain molecule from
repeated units. Randomly cross-linking a long natural-origin protein
(I don't hold this view myself)
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