What, exactly, is patina?

[Edward Miller]

I have a mix of tools--some new, some old. I feel like every time I turn around, my shiny new Lie-Nielsen #7 has a spot of rust on it somewhere, despite my best efforts. Contrast this with my roughly 100-year-old Stanley #5 that never rusts. And that's pretty typical in my shop. New tools need to be vigilantly protected from rust, while old tools are fine as is. Why? What, exactly, is this magical patina that prevents rust, and how could I promote its development on my newer tools?

Anybody know?

[george wilson]

Guns are blued or RUST BLUED to protect them against rusting. Of course,these finishes do not prevent rust,but they slow it down a bit from starting.

Your old Stanleys,which I imagine are dark looking as opposed to shiny and bright,have a natural occurrence of this "rust bluing",and probably over the years have also absorbed a certain amount of oil,from their irons being sharpened on oil stones(Which used to be the ONLY commonly used type stone in the USA),as well as oil from hands. Cast iron is porous and can absorb some oil. We used to "season" cast iron frying pans by heating them up when full of oil. As they cooled off,some oil was further sucked in.

So,this is likely why your old tools don't rust as readily. Try keeping your new plane oiled. Wipe it off before use. It will get oil into the cast iron,too. But perhaps not as readily as old cast iron. The new planes are made of malleable iron,which is cast iron with the excess carbon baked out of it at high temperatures for hours. It might not be as porous as regular cast iron. I'd have to research it.

[bridger berdel]

In short, patina is the visible effect of age. As iron ages the corners wear a little, the faces get scrapes and dings, the polish of manufacturing fades and the surface shows signs of chemical interactions with it's environment. Much of that is iron oxide, the same rust you find so unsightly when it's a spot in the middle of a polished surface. Some is the effects of iron interacting with other chemical compounds. Small amounts of sulphur will turn iron jet black if the conditions are right. George is right on about the effects of oil on iron.

I really like the look of aged patinated iron rubbed smooth by time and put to work with a coat of paste wax. I have a very nice #3, type 10 or so that some well meaning soul did a complete restoration of. All the iron surfaces were polished, the lever cap was nickle plated and the japanning was stripped and either re-japanned or painted. I prefer the more naturally aged planes. I have a woodriver #1 plane, all shiny and new. Every time I pull it out I think about ways to make it look old....

[Patrick Chase]

Unlike Bronze Iron doesn't develop patina in the sense of a chemically passive oxide that occurs without any sort of coating or conversion process.

George outlines one strong possibility: Iron has multiple oxides, of which rust (Fe2O3) is the most problematic one. Magnetite (Fe3O4) is more stable, so if you can convert the surface layer to Magnetite then you can delay (not indefinitely) the onset of rusting. Bluing is a family of electrochemical conversion processes to do just that. The problem here is that Magnetite doesn't "just happen" on its own the way a Bronze patina does, and it should be pretty obviously dark if it's there. It should be the color of a black oxide drill bit ("black oxide" is nothing more than Magnetite).

One other possibility is the difference in Iron composition and grain structure. The old Stanleys are conventional cast gray iron, while the L-N is ductile iron. Totally shooting from the hip here, but the latter may be more rust prone. Now that I think about it I'm pretty sure I've encountered more rust on my ductile iron Veritas planes than on older ones, though it's been a nonissue since I got serious about prevention (short summary: CRC 3-36, liberal use of VCI squares and sometimes capsules, VCI paper for long-term storage, thorough drying/oiling after water exposure).

[george wilson]

I mentioned that there could be a difference in porosity between the malleable iron LV and LN planes,and plain old cast iron. So we agree on that,but you might Google about it and check it out,Edward. In any case,keep a light coat of oil on your new planes,and do wax them,too.

[Kees Heiden]

Okay, I don't really know the answer but I do have a theory

You see a similar corosion resistance in wrought iron. Wrought iron has various layers, some are more ferrous, other more carbonous. Those carbonous layers rust a lot less quickly. They kind of form a barrier for the oxygen to go deeper. At least that is how I understand the process.

Gray iron has about the same amount of carbon as nodulair or ductile iron. In gray iron the carbon forms layers around the ferrous crystals. In nodulair iron the carbon clusters in small balls and sits in between the various ferous crystals, like you can see very well in this picture:



This comes from this website: http://www.iron-foundry.com/grey-iro...ular-iron.html

As you can see, the carbon in gray cast iron tries to surround the ferrous crystals, so I could imagine that this makes the metal more corrosion resistant.

Of course, leave the old Stanley plane in a humid garden shed for a couple of years and it will have rusted nicely too.

[Patrick Chase]

I mentioned that there could be a difference in porosity between the malleable iron LV and LN planes,and plain old cast iron. So we agree on that,but you might Google about it and check it out,Edward. In any case,keep a light coat of oil on your new planes,and do wax them,too.

You're right, you did. I didn't acknowledge that because of less-than-thorough reading on my part. Sorry about that.

[mike holden]

Patina

: a thin usually green layer that forms naturally on the metals copper and bronze when they are exposed to the air for a long time
: a shiny or dark surface that forms naturally on something (such as wood or leather) that is used for a long time
: a thin layer

-Merriam Webster Dictionary

In other words, corrosion, dirt, wear, and age

Did You Know?

Italians began using "patina" in the 17th century to refer to the green film that is produced on the surface of copper. They borrowed the word from Latin, where it means "a shallow dish." (Presumably, the Italian meaning developed from the observation of such film forming on copper dishes.) By the mid-18th century, English speakers were also calling the green film "patina." And by the early 20th century, "patina" was being used in English for the gloss of polished metals, like silver, as well as wooden furniture - a meaning that led to its literary use for a surrounding aura, as demonstrated in this quote from Stella Gibbons' Cold Comfort Farm (1932): "The very atmosphere seemed covered with a rich patina of love."




It's like being "cool" if you got it, you got it. You cant go out and get it.
Mike

[Bill White]

Having fought the rust issue for many years, I came upon the Paul Sellers posting about the stupid simple "oil pot". Just a small can with a coiled rag impregnated with oil.
I use it after each use, and it keeps the planes/chisels lubed lightly. Does not seem to change any patina.
Plain old 3 in 1 oil.
What's not to like?
Bill

[Patrick Chase]

Okay, I don't really know the answer but I do have a theory

You see a similar corosion resistance in wrought iron. Wrought iron has various layers, some are more ferrous, other more carbonous. Those carbonous layers rust a lot less quickly. They kind of form a barrier for the oxygen to go deeper. At least that is how I understand the process.

Gray iron has about the same amount of carbon as nodulair or ductile iron. In gray iron the carbon forms layers around the ferrous crystals. In nodulair iron the carbon clusters in small balls and sits in between the various ferous crystals, like you can see very well in this picture:

This comes from this website: http://www.iron-foundry.com/grey-iro...ular-iron.html

As you can see, the carbon in gray cast iron tries to surround the ferrous crystals, so I could imagine that this makes the metal more corrosion resistant.

Of course, leave the old Stanley plane in a humid garden shed for a couple of years and it will have rusted nicely too.

That argument makes sense, though I don't know enough to know if it's actually right :-).

I would note that even if it is more rust-prone I think that ductile cast iron is a better material for metal planes. You can avoid rust on ductile iron easily enough, but there's no way to make grey iron stronger or less brittle.

[Kees Heiden]

I don't know if I am right either...

Maybe better wait for a real metallurgist to add her/his knowledge.

BTW, another disadvantage of ductile iron is, it scratches easier. Old gray cat iron is quite a bit harder. So, as long as you don't drop the plane on a stone floor, the oldies seem to be a little "better".

[Mike Brady]

I mentioned that there could be a difference in porosity between the malleable iron LV and LN planes,and plain old cast iron. So we agree on that,but you might Google about it and check it out,Edward. In any case,keep a light coat of oil on your new planes,and do wax them,too.

I'm no metallurgist, but I concur that my L-N iron body planes are slightly more rust prone than my old Stanleys. I'm not saying its a problem, but I am pretty religious about keeping the castings wiped off after use and sharpenings. I use that spray made by Boeing. Boeshield.

[Rich Riddle]

Patina is a nice word for rust as replica is a nice word for copy or fake.

[Patrick Chase]

I'm no metallurgist, but I concur that my L-N iron body planes are slightly more rust prone than my old Stanleys. I'm not saying its a problem, but I am pretty religious about keeping the castings wiped off after use and sharpenings. I use that spray made by Boeing. Boeshield.

I used to use that. I think there are better options.

If you store your tools in an enclosed space then corrosion inhibitors are an option, whether of the new sort (VCI) or Camphor.

CRC 3-36 works better than Boeshield for me. Boeshield relies on depositing a dry wax film on the metal surface, and that can be rubbed or scuffed off fairly easily. 3-36 and a couple of the others create nondrying films that are somewhat self-healing. They all use volatile aliphatic (non-aromatic, not-Benzene-like) hydrocarbons as vehicle/solvent. The respective MSDSs say they're all pretty safe (much more so than, say, Kerosene, which can have significant aromatic content), but some folks may be sensitive anyway so take that for what it's worth.

[Patrick Chase]

Patina is a nice word for rust as replica is a nice word for copy or fake.

Its meaning is much more specific than that. Patina is the stable thin film of visible oxidation that forms on Bronze etc. Rust (Fe2O3) is certainly visible oxidation, but it isn't a film, doesn't stay thin for long, and certainly isn't stable.