Full Chisel Blog

July 23, 2010

Linseed oil on Metal

Filed under: Finishing,Hardware,Historical Material,Of Interest,Techniques — Stephen Shepherd @ 7:44 pm

 

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

37 Comments »

  1. 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

  2. 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

  3. 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

  4. And so I learned something today. Thanks.

    Comment by Luke Townsley — July 23, 2010 @ 8:35 pm

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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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    Pingback by Corrosion - Woodwork Forums — August 9, 2010 @ 7:28 am

  13. Does anyone know if a linseed oil will work on a cast iron fountain? It had some kind of oil rubbed on it when new, but after a season, that is gone. I would like to condition it before I cover it for winter and wanted to use an oil that made it black again and to make it last longer.

    My main concern is to avoid using an oil that will spoil the water next year and/or harm the birds that bathe in and drink from the top basin.

    Comment by Michael — September 20, 2010 @ 12:05 am

  14. Michael,

    Linseed oil will work just fine on cast iron. Clean the surface and apply the oil, wait 10 minutes and wipe off the excess. It helps if the iron piece is warm, do it on a warm day if possible. The birds will be just fine.

    Stephen

    Comment by Stephen Shepherd — September 20, 2010 @ 7:20 am

  15. I am a painting contractor looking for input on some hot rolled metal (steel)that was designed for some staircases. We need to clean it up a bit and apply a protectant. Urethanes are not an option. This is a green building. Should I clean with laq. thinner or something else. Would lindseed oil give the metal a cleaner look? Thanks

    Comment by Dave — January 4, 2011 @ 6:41 pm

  16. Dave,

    Welcome. I would wash the metal down with a good soap [not detergent] to remove manufacturing oil and grease,and rinse it well. After it has dried then wipe it down alcohol, ethanol is the ‘greenest’. Then apply a coat of boiled linseed oil, wait 10 minutes and wipe off the excess. Be sure to remove all of the extra oil so it doesn’t become sticky. Should be dry in 24 hours. Dispose of oily rags properly.

    Stephen

    Comment by Stephen Shepherd — January 4, 2011 @ 7:15 pm

  17. I used boiled linseed oil with a little bees wax ( nickle size ball disolved in naphtha for a quart) to coat 80 year old wrought iron. The iron is outside in Florida and with no paint and looks great. I avoid heavy a oats so it does not build up. I apply 2x per year.

    Comment by David — January 18, 2011 @ 9:55 pm

  18. Boiled linseed oil of the shelf is toxic. It has not been boiled, it is a chemical cocktail to make it think it’s been boiled ( and you for that matter).. Boil your own if you must. I have used Raw Linseed Oil for over 30 years as a Blacksmith. To protect iron and indeed conserve/preserve it just liberally paint Linseed on with a brush. Do this outside on a warm day, or if in Winter warm oil a little to thin it. Do not clean iron first, particularly heavy corrosion areas which have become a crusty lump. Cleaning will only break the crust that is now holding it all together and expose the bare iron to oxygen and moisture accelerating the corrosion. Let the oil drain off and leave what is left just wiping drips from lower edges. The oil penetrates and then oxidises from the surface down giving a flexible waterproof coating that will help hold the ironwork together, protect it from the elements of corrosion until a restoration can be programmed or just put it in a holding pattern with a fresh application on a dry warm sunny day once a year. Linseed oil is cheap and safe and can be coloured if so chosen and will give you the best paint finish ever. The Royal Armoury (UK) has done tests that says Linseed Oil corrodes Iron. I would argue that most of the ancient Ironwork we have in museums today was treated with Linseed at manufacture and during use and therefore is at least partly responsible for the reduced corrosion that has preserved the artifact until found centuries later. I will continue to use Linseed Oil to treat my Ironwork in the hope that one day in the distant future, someone will dig up a piece made by me and prove the point perhaps. Linseed warmed on Iron goes through several colour changes including a deep mahogany red through to shiny Black. Apply thinly for this purpose or the Oil will skin wrinkle with the accelerated curing. I use the oily rags to light my forge. Have fun. Pete.

    Comment by Pete Smith — September 11, 2011 @ 7:32 am

  19. I am restoring a vintage WWII rifle and I am using boiled linseed oil on the stock. It has some parkerized banding that is pressed on, so I left it in place. When I oiled the wood, I couldn’t help but oil the metal as well. It looks great! I am considering oiling the rest of the exposed metal (I don’t think I will use it on the internal parts). Has anyone used linseed oil on metal with a finish on it. Like bluing, anodizing, parkerizing, plating, etc.?
    Thanks,
    Peter

    Comment by Peter Dale — November 26, 2011 @ 12:47 am

  20. America’s test kitchen did some interesting tests on cast iron to season (cure). Food grade linseed oil cured at ~ 300 deg for 5 hours proved to be a thin and tough coating. Shed oil and water like Teflon avoiding the brain issues. Have used on old metal ATC tanks to seal after cleaning rusty inside with diesel and epoxy fish tank gravel. Thin boiled linseed oil with heat works like a charm on top of the wood stove in the barn to heat and dry. Much better than epoxy or other inside tank finishers, 2 years on and no rust inside tank. Light coating on wooden handles and metal blades is perfect to winterize. Seems to recondition the wood and seal the metal.not sure about it causing rust maybe when its older and breaking down?

    Comment by robb willes — December 4, 2011 @ 3:11 pm

  21. Linseed oil is wonderful for axes and knives Is a wet condition . Light coats do wonders .., of course also protects wood. Always happy with this most basic application .

    Comment by Ray Mears — February 15, 2012 @ 12:34 pm

  22. i asume linseed oil is toxic and not for human consumption is there anything i can use in its place .i am making spoons & forks out of sheet metal and think the metalic taste is a good sign some sort of treatment is needed

    Comment by auggie — April 10, 2012 @ 7:55 pm

  23. auggie,

    You might try walnut oil, a drying oil that is also a salad oil.

    Stephen

    Comment by Stephen Shepherd — April 11, 2012 @ 10:21 am

  24. “For those of you WHO are of the same opinion…” Right on oil, dodgy on grammar. ;)

    Comment by Sara Corter — February 18, 2013 @ 9:59 am

  25. I need to seal a sheet of steel that will be placed behind a wood stove to protect the wall for fire safety. If I coated the sheet with linseed oil for rust protection will the surface become flammable? Will the constant heat melt off the linseed oil?

    Comment by Vanessa — February 24, 2013 @ 3:32 am

  26. Sara,
    I never get that right, I should learn the rules, where is my copie of ‘Elements of Style’?

    Vanessa,
    Once the linseed oil is dry the thin film is too thin to ignite.

    Stephen

    Comment by Stephen Shepherd — February 25, 2013 @ 9:32 am

  27. auggie,
    who said flax seed oil is harmful for consumption? i have been eating raw oil for years. i am fine. a lot of people eat it. its very good for health.

    Comment by mak — March 8, 2013 @ 11:33 am

  28. Hi Stephen,

    Your blog seems to be the most likely source I’ve encountered for an authoritative response to a question I’ve been trying to research (without much luck)on the internet: What is the shelf life of pure linseed oil? I have a half full can of Sherwin-Williams “pure raw linseed oil”. In smaller print below it is “aged – filtered” and “Always Pure – Always Dependable”. This is a can I inherited from my dad who used to do some woodworking. It’s probably a 1950s vintage! Any chance it’s still any good? It is still liquid, about the consistency of a lightweight household or vegetable oil (which I guess it actually is). Think Sherwin-Williams will stand by their claim of “Always Dependable”? Sorry don’t have the original receipt.

    Comment by David S. — June 16, 2013 @ 3:12 pm

  29. David S.

    If it is still liquid it is good. Even if it is thickened it has become stand oil which will dry quicker when applied. Linseed oil of any type should always be thinned with turpentine [no other solvent] for use and should never be used straight. Just thin it out with a bit of turps and it is good to go. I talk about this in Shellac, Linseed Oil & Paint – Traditional 19th Century Woodwork Finishes, my recent book, available from the Full Chisel Store, there is a link in the upper right.
    Stephen

    Comment by Stephen Shepherd — June 16, 2013 @ 3:33 pm

  30. Hi Stephen,

    First of all, thanks for the excellent info about linseed oil!

    I’m in the process of restoring an old Kerosene lantern. WT Kirkman (WT Kirkman Lanterns, Inc.) recommends using a 50/50 mix of Kerosene and boiled linseed oil for finishing a restored “bare metal” lantern. In your opinion does this sound like a reasonable mixture? Also, any ideas on Ballistol?

    Comment by Bill Weismuller — June 26, 2013 @ 7:16 pm

  31. Bill,
    I would suggest turpentine rather than kerosene because I do more traditional woodwork so I use the traditional ingredient. Should work just fine on bare metal. Don’t know what Ballistol is.

    Stephen

    Comment by Stephen Shepherd — June 27, 2013 @ 7:18 am

  32. Hello again Stephen,

    My lantern(s) turned out really really nice, I’m very impressed!! I used 3 to 4 coats of 50/50 BLO and turpentine and baked each coat for a couple of hours at about 200 degrees. The heat darkened the finish beautifully.

    I’m working on a lamp now that is going to be partially painted, can I apply BLO over the paint? I’d like to give it a coat of oil before painting but I imagine the paint wouldn’t adhere very well over it.

    Thanks for your help.

    Bill W.

    Comment by Bill — November 13, 2013 @ 2:10 pm

  33. Bill,
    Glad you lanterns worked out. You can put blo/turps over painted finishes and you can paint over blo/turps after it has dried completely.
    I go over how this all works in Shellac, Linseed Oil, & Paint – Traditional Nineteenth Century Woodwork Finishes, available from the Full Chisel Store or on Amazon or from Tools for Working Wood or from Lee Valley.
    Stephen

    Comment by Stephen Shepherd — November 13, 2013 @ 2:33 pm

  34. I am in the process of experimenting with bluing metal for a project on firearms restoration.

    I finished a few test pieces, and first i tried coating the blued metal with regular gunoil, butbthat left the surface with fingerprints every time you handled it. I the tried linseed oil, and put on the thinnest coat i could, let sit for 10-15 minutes and buffed it off and left it to dry on a radiator over night.

    Surface is dry to the touch, feels a bit slippery, and most important, does not take fingerprints.

    So i can confirm that it works on steel.

    I have not tried thinning it with turpentine, but will try that next time. Mineral og vegetable turpentine, what should i use? Vegetable sure smells the nicest.

    Claus

    Comment by Claus Christensen — April 7, 2014 @ 6:00 am

  35. Claus,
    I am glad you got good results. I have never heard of mineral turpentine you should use vegetable turpentine from trees. Always thin linseed oil with turps, never use it straight.

    Stephen

    Comment by Stephen Shepherd — April 7, 2014 @ 8:06 am

  36. Hi stephen,

    I used oil paint with Linseed stand oil for repaint my old jewelry. Came out beautiful but wondering is it safe for the skin? Any advise will be greatly appreciated.

    Asha

    Comment by Asha — May 14, 2014 @ 11:10 am

  37. Asha,
    Linseed oil if perfectly safe.
    Stephen

    Comment by Stephen Shepherd — May 17, 2014 @ 8:57 am

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