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Old 09-20-2008, 11:44 AM   #1
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Linseed Oil


What is the difference between 'boiled' and 'raw' linseed oil? When to use which or the do's and don'ts of each. Lables never mention one from the other.

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Old 09-20-2008, 02:02 PM   #2
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Linseed Oil


Boiled Linseed Oil dries quicker. What are u planning to do with the lindseed oil ?

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Old 09-20-2008, 02:02 PM   #3
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Linseed Oil


"Boiled" is well, boiled. No pun intended, but the boiled has been heated to boiling to remove most of the moisture content. Raw linseed oil, with the natural moisture content, will take much longer, if at all, to dry.

At least that has been my understanding the past 40 years.
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Old 09-20-2008, 02:29 PM   #4
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Linseed Oil


I think raw lindseed oil will never really dry.
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Old 09-20-2008, 04:05 PM   #5
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Linseed Oil


It's one of those odd things that you probably wouldn't be using unless you knew how and why you were using it, and it's used for multiple and quite varied uses...most of them very Old School

Mixing it with cement for plumbing connections?
Sealing your wood gutters?

What you want and why....and any mixture recipes depends on what you are doing with it
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Old 09-21-2008, 08:43 AM   #6
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Linseed Oil


slickshift,
Who are you calling "Old?"
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Old 11-06-2008, 10:43 AM   #7
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Linseed Oil


If I was planning to put some linseed oil on an old wooden hammer handle would you recommend boiled or raw?

I'm guessing boiled based on what's been said above about drying, but like the original poster said, labels on bottles are pretty vague on recommended uses.

Boiled and raw are the same price where I am though, so I'm just looking for whatever's best for the wood (hickory).

Sam.
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Old 11-06-2008, 10:46 AM   #8
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Linseed Oil


I don't know if you really want to use either on a hammer, but ulness you want a slippery handle for the next 2 years, use boiled. Your thumb will thank you for that
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Old 11-06-2008, 11:17 AM   #9
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Linseed Oil


Thanks Matthewt1970.

Is there a specific wood-treatment/preserver you'd recommend on a hammer handle in place of linseed oil (boiled or raw)?

I'm pretty open to suggestions.

For what it's worth, this particular hammer doesn't get much use, it's more of a "family heirloom".

Sam
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Old 11-06-2008, 06:39 PM   #10
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Linseed Oil


Quote:
Originally Posted by bobat View Post
What is the difference between 'boiled' and 'raw' linseed oil? When to use which or the do's and don'ts of each. Lables never mention one from the other.
Welcome to DRYING OILS 101:

Linseed oil is oil that is produced by squashing flax seeds.

When linseed oil is exposed to air, it absorbs oxygen molecules from the air, and those O2 molecules form a PAIR of C-O-C crosslinks wherever there are two unsaturated sites in close proximity. It's those C-O-C crosslinks that form in a process called "auto oxidation" that is the basis of drying oils, alkyd paints and polyurethane "varnishes" all drying to form solids.

OK, but what's an "unsaturated site"?

Here's where I temporarily fly off on a tangent...

Crude oil, is totally saturated. It looks like polyethylene, or like this:

-HCH-HCH-HCH-HCH-HCH-HCH-HCH-HCH-HCH-HCH-HCH-HCH-HCH-HCH-

where every carbon atom in the chain is bonded to the carbon atom on each side of it and to two additional hydrogen atoms (above and below it, say). That is, in a saturated oil like crude oil, you have a string of carbon atoms, and each carbon atom has two hydrogen atoms bonded to it. So, each carbon atom forms 4 bonds; one with the carbon atom on either side of it, and one with each of the two hydrogen atoms bonded to it. Since carbon has a valence of 4, there are no more locations where any addition hydrogen atoms would fit.

Natural oils, like corn oil, soy bean oil, coconut oil, linseed oil, and olive oil will invariably contain "unsaturated sites" where a double bond forms between two carbon atoms, and so there is only ONE hydrogen atom bonded to each of those two carbon atoms. Like this:

-HCH-HC=CH-HCH-HCH-HC=CH-HCH-HCH-HCH-HCH-HCH-HC=CH-HCH-

There are three "unsaturated sites" in the above vegetable oil molecule. Can you find them? When food labels say "unsaturated fats" or "unsaturated oil", this is what they're referring to. It's those double bonds between carbon atoms that make an oil or fat "unsaturated" because it's not completely saturated with hydrogen atoms.

Most natural animal fats and vegetable oils (and animal oils like fish oil or whale oil) have very few of those unsaturated sites, and they are called "non-drying" oils. Some, like soy bean oil have enough unsaturated sites that if exposed to air for a few years, they become much more viscous. These are called "semi-drying" oils.

However, some naturally occuring oils have enough of those unsaturated sites that, when exposed to air, they dry to a SOLID. Linseed oil, Tung or (Chinawood) oil, Oiticia oil, castor oil, safflower oil, tall oil and some fish oils are "drying oils" because they will, over the course of one to several months gradually dry to a solid. But, it takes a long time (at least a month) for a drying oil to dry to a solid. But, if you could see into that drying oil after it has solidified, you would see that at each location where two unsaturated sites were in close proximity, the oil molecules were connected by a PAIR of C-O-C crosslinks, which used to be an oxygen molecules in the air.

Back to the chase:

They haven't actually "boiled" any linseed oil to make "boiled linseed oil" since the 1930's or 40's. When you do that, you heat oil that already has the O2 molecules absorbed into it. The result is "partial polymerization" of the oil, which is just a fancy way of saying that instead of individual drying oil molecules in the pot, you NOW have lots of "clumps" of drying oil molecules where the oil molecules within each clump are loosely crosslinked together. That is, there is some crosslinking within each clump holding the oil molecules in that clump together, but there is no crosslinking between different clumps. The result is that the oil is more viscous and "dries" much faster when exposed to air. The reason why is that many crosslinks were already formed at the higher temperature (in the boiling process) and for the boiled oil to now form a soft film, all that has to happen is that the clumps of drying oil molecules have to crosslink with each other. And, as more crosslinks form within that soft film, it gradually becomes harder and harder. This is what happened with true drying oil based paints years ago, back before WWII.

Nowadays, no one boils linseed oil because the "partially polymerized" oil doesn't penetrate as well into wood as raw linseed oil does. That's cuz individual oil molecules are much smaller than those "partially polymerized "clumps", so that they can migrate more easily and deeper into wood for better adhesion to the wood. The deeper the penetration, the better the adhesion of the drying oil based primer or paint to the wood. Also, the partially polymerized oil is more viscous than the raw oil, so you need more turpentine to thin it to a paintable consistancy, and the more turpentine you add, the longer the drying time.

Nowadays, "boiled" linseed oil is nothing more than raw linseed oil with certain metallic salts added to it that act as catalysts in that crosslinking reaction with oxygen molecules (O2) from the air. The metals involved are arsenic, cobalt, manganese and I don't think they use lead anymore.

http://bechchem.com/chemical_dryers.php

So, by using those metallic salts as a catalyst, the raw oil penetrates into wood deeper and more easily for better adhesion, requires the least amount of thinner, and still dries in only a couple of days just like real boiled linseed oil.

The problem is that adding arsenic or cobalt or lead makes the "boiled" linseed oil INEDIBLE. So, for people wanting to use a linseed oil as a finish on a wood bowl turned on a lathe, raw linseed oil is the only option. Similarily, if someone carves a pair of salad mixing spoons out of wood, you'd want to use a raw drying oil on them, like raw linseed oil, not something with arsenic, cobalt and maybe lead in it. (I don't know that manganese is dangerous to ingest.)

Another use of raw linseed oil is in glazing windows. Glazing putty is nothing more than a mixture of clay and raw linseed oil. People that do a lot of glazing will be pretty particular about how they like their glazing putty. Those people can "thin" their glazing putty with raw linseed oil to both soften it and make it more to their liking so that they can get a smooth bead of putty on the window with a putty knife more easily.

Also, in order to get the glazing putty to stick to the wood better, it's common to paint the wood frame with raw linseed oil, and then wipe off the excess oil before glazing. That way, crosslinks form between the oil in the wood and the oil in the putty, ensuring excellent adhesion between the two.

Finally, years ago people used raw linseed oil as a preservative for wood and ropes made of natural fibers. Nowadays, the chemical preservatives like copper and zinc naphthenate are very much more effective than linseed oil, and nylon and polypropylene make for much stronger ropes and need no preservative to keep them from rotting. But, some people will still ask for raw linseed oil for use as a preservative, so stores still sell it. It's a product that's best years are behind it, but the demand for which hasn't completely disappeared yet (think vaccuum tubes and slide rules).

So:
a) Yes, raw linseed oil will dry to a solid, but it'll take a month or more. This is why window glazing putty gradually dries to a solid.
b) boiled linseed oil isn't boiled anymore. Nowadays it's catalyzed with stuff you don't want to swallow.
c) raw linseed oil is still used for wood surfaces that will be used to prepare or serve food, and for glazing windows. And...
d) Water doesn't dissolve in oil (and vice versa), so the purpose of boiling linseed oil would not be to reduce it's moisture content. There is no moisture in the oil to begin with. Nothing, zip, zilch, nada. No water in the oil to begin with, and no reason for that to change with time. Also, water plays no role whatsoever in the mechanism whereby drying oils form solids, so reducing the moisture content of the drying oil (if that were possible) wouldn't affect it's drying time.

Last edited by Nestor_Kelebay; 11-07-2008 at 01:40 AM.
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Old 11-06-2008, 06:55 PM   #11
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Linseed Oil


Quote:
Originally Posted by Fitzsamuel View Post
Thanks Matthewt1970.

Is there a specific wood-treatment/preserver you'd recommend on a hammer handle in place of linseed oil (boiled or raw)?

I'm pretty open to suggestions.

For what it's worth, this particular hammer doesn't get much use, it's more of a "family heirloom".

Sam

Sam: The best coating on the hammer would be polyurethane. However, if this is a valued family heirloom, you'll want to use the coating that was most likely originally used when the hammer was made. That was probably real varnish. You probably won't find real varnish for sale at any hardware store. However, it's still used on musical instruments made from wood, so any place that sells or repairs musical instruments will know where you can buy some real varnish.

PS: Varnish is nothing more than boiled linseed oil with the dried resins of certain plants (called "copals") dissolved in it, and the whole mixture thinned with turpentine. Essentially, a true drying oil based paint has exactly the same recipe, but contains less copals, and contains copals of lower quality (which impart less hardness and more colour). Polyurethane, first patented by the Bayer Company (the Aspirin makers) in 1956, has replaced varnish as the clear coat of choice over wood.
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Old 11-07-2008, 11:20 AM   #12
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Linseed Oil


I don't know if I can really call it a "valued" family heirloom... it's more one that we won't throw out because we've had it for as long as anyone can remember, though if there's any heavy work to be done we'll use a newer hammer we have lying around.
Given how the handle on this one was in a fairly sorry state I thought I'd see if there's anything straightforward I can do to improve it.

Loved the explanation of the chemistry of it all - certainly the stuff about saturated and unsaturated hydrocarbons sounds like something I once studied in High School

Regards,
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Old 05-20-2011, 04:22 AM   #13
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Linseed Oil


Quote:
Originally Posted by Nestor_Kelebay View Post
Welcome to DRYING OILS 101:
Hi, I'm new to this forum and I have a question to Nestor Kelebay (or anybody else for this matter )

This thread is a bit old but I give it a shot anyway, hope you can help me out.

I've been boiling linseed oil sometimes for painting purposes. In 2004 I've read an old recipe where you boil linseed oil on water so the bubbles of the water burst through the oil, keeping the oil at 100 deg C. This simmers for 4 hours. Now, besides water250ml and oil 500ml, you add 20 gr of pumice powder and 10 gr of boneblack powder... here's my question:

What could be the purpose of the boneblack powder?

I know one of the purposes of the pumice powder is to avoid the oil from spattering all across the kitchen.

After the boiling process I transfer the concoction into a glass bowl and make it settle so a precipitation forms at the bottom. I separate the oil from the water and pour it into a silver flat dish, allowing it to bleach and thicken in the sun until it's like a slightly viscous honey.

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