This is spawned from a rather silly thread on a Woodworking forum on the Internet. Someone asked if linseed oil could be used on metal, particularly woodworking tools to prevent rust. The response was that linseed oil left a gummy film on the tools and they recommended all sorts of petroleum distillates to use instead.
Obviously some of the people responding have never learned to wipe off the excess before it dries. This will indeed form a gummy film and cause problems. The recommendations to use mineral oil [a laxative] or paraffin oil in one form or another to protect metals. If you are going to use petrochemicals on metal use something cheap like 30 weight motor oil, it will protect the metal with a non drying oil. People even recommend mineral oil for wooden food utensils, because it never dries it comes out in the food and is particularly harmful to wood which is a natural product and the synthetics are not. Then there is that laxative thing.
Linseed oil has been used as a metal finish and rust protector for centuries. Yes that is hundreds and hundreds of years. Linseed oil is used to quench hot wrought iron to give it a nice black finish. Linseed oil is also used to finish the iron by heating it up and dunking it in linseed oil. Linseed oil is a long bond double molecule, and while it sounds big it is actually very small and will penetrate into anything from iron and steel to woods and other porous materials and even smooth modern plastic laminates.
When done properly linseed oil will offer fine protection from rust to any ferrous metal. The key word is properly, that means wiping off all excess. That means there is no extra oil left on the surface, and this is where people end up with a gummy finish, they don’t get all of the oil. A thick coat of oil will dry from the outside in by forming a skin on the surface, preventing the oil underneath from drying, hence a sticky mess. A very thin coat will dry quickly and not have that problem.
Living in the dry arid West, rust is not that much a problem unless using green or partially dried wood, in which case the wood and the shavings will cause rust if left in contact with unprotected metal surfaces. Using wooden hand planes the only rust occurs on the irons so having some protection on the irons does help reduce the problem as does removing shavings completely before storing. Also sawing damp wood can cause problems especially with the swarf left in the teeth of the saws. My saws are all made from old, usually pitted blades that have been cleaned of surface rust, using a variety of methods. The blades are then heated up and treated with linseed oil, the excess wiped off and allowed to cure. The sharpening removes any oil from the teeth, so they can be vulnerable to rust.
The tools don’t gum up because they don’t have a thick film on the surface. The old iron and steel are protected from rust, except on their sharpened edges. Linseed oil was also used on firearms, on both the wood and metal parts for the very reason that if properly applied it offers protection to the wood as well as protecting the metal from rust. It is also the traditional finish, again when properly applied, to much of the iron hardware used on furniture and other wooden objects during the nineteenth century.
For those of you whom are of the same opinion, I apologize for being redundant, for everyone else, I believe that you are all entitled to my opinion.
Stephen
I wasn’t aware of the use of linseed oil in metalworking – so I find this useful and inspiring. Thanks for posting. I’m off to do some experimenting.
Tim
Comment by Tim Lawson — July 23, 2010 @ 8:10 pm
Very interesting Stephen. I assume you’re talking about raw linseed oil? I’ve read lots of info about this in the past few months, and found the info somewhat confusing as some writers used the term “linseed oil” and “boiled linseed oil” interchangeably.
Comment by Jameel Abraham — July 23, 2010 @ 8:15 pm
Tim,
Their history goes back a long time. Also thinning with a bit of spirits of turpentine will raise the viscosity, help in drying as well as adding its own properties.
Jameel,
I am one of those writers that use the term linseed oil when speaking of boiled linseed oil. It works for both and while I couldn’t get raw linseed oil in quantities I did use expensive Flax Seed Oil from health food stores in its stead. Boiled linseed oil, is a crap shoot in that the nature of the driers, usually metallic driers are dangerous and there are warnings on the cans. Some makers I do believe make boiled linseed oil that is actually kettle boiled [heated up to at least 225 degrees (F)]. There are many ways to boil the oil without adding nasty chemicals.
I will be covering this all in my next book on traditional 19th century furniture finishes.
Stephen
Comment by Stephen Shepherd — July 23, 2010 @ 8:32 pm
And so I learned something today. Thanks.
Comment by Luke Townsley — July 23, 2010 @ 8:35 pm
I’m not sure that I can believe this, Stephen. After all, George Wilson disagrees with the suitability of linseed oil for this purpose. :@)
Comment by wilbur — July 23, 2010 @ 8:37 pm
Hi Stephen
This is pretty interesting. You allude to the use of mineral oil on kitchen utensils and I take it that, you don’t recommend the use of laxatives as finishes! What finish should you use on utensils?
Thanks,
Comment by Praki — July 24, 2010 @ 8:16 am
Stephen,
You are spot on about using linseed oil to protect metal. Linseed oil has been the traditional protectant for fire axes and implements since the earliest days. It is still the best option I have found for long lasting protection that is not slippery. We use several all metal tools in the fire service that need rust protection, but still allow someone to grip the tool. Boiled linseed oil fits the bill perfectly. Another traditional use was for fire axe handles. Combining crushed walnut shells with the oil around the bottom of the handle to increase grip and protect the wood.
Sincerely,
Mike
Comment by Mike — July 25, 2010 @ 5:45 am
Luke,
It is always a good day when one learns something, glad to help.
wilbur,
You blew my cover and exposed my source.
Praki,
I use walnut oil, readily available in the salad oil section in most grocery stores or health food stores. It is a drying oil, unlike [laxative] mineral oil which never dries. People say that it can get rancid but I have never noted that, I have some small tool handles that are also finished with walnut oil.
Mike,
Welcome and thanks for the tip of adding crushed walnut shells to improve grip.
Stephen
Comment by Stephen Shepherd — July 25, 2010 @ 7:43 am
Raw linseed oil half and half with real turpentine is perfect for metal, wood and probably everything. The turps helps it flow into nooks and crannies and it evaporates leaving a thinner film of oil. The oil doesn’t “dry” BTW it oxidises – hence the oxidised skin on oil applied too thickly – the oil underneath will stay liquid for a very long time.
“Boiled” linseed oil has hardeners added to speed up the process, traditionally lead, but it’s still oxidation, not drying.
Comment by jacob — July 31, 2010 @ 1:29 pm
Jacob,
Linseed oil is called a ‘drying oil’, like poppyseed oil, walnut oil and hemp seed oil, and the term is used to distinguish it from ‘non-drying oils’ such as olive oil, etc. It becomes hard by polymerizing and oxidizing.
Stephen
Comment by Stephen Shepherd — August 1, 2010 @ 9:27 am
I have used linseed oil finishes for years. Never considered it for metal. I have tried every commercial treatment to prevent rust on my muskets but have found bacon fat to work the best, so far. Will definately test Linseed oil next time.
Comment by John Dwyer — August 5, 2010 @ 10:12 am
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