A disease.? Granted I beat up on that old Stanley chisel building fences, a deck and a shed and there was a neglected rust spot on it for awhile. But I cleaned it up along time ago. Now the metal at that spot has sort of eroded away a little and there's a black spot there. Doesn't look like rust.. I sanded on it today with some wet and dry sand paper some came off. What's with the black. Is this black rust?
When you polish/sharpen the chisel, it creates fine metal particles which appear black to normal vision. These may have collected in the etched spot.
It's iron oxide.
Contrary to popular belief, rust and iron oxide are in fact not the same thing. Rust is *hydrated* iron oxide (iron oxide plus water). When iron or steel gets wet and begins to rust, it's actually a two-step process: the water accelerates the formation of iron oxide -- which is black -- and then combines with the top layer it to form rust. When you remove the rust, there's still going to be a spot of black iron oxide beneath it.
Which eventually flakes off (disintegrates? evaporates?) and leaves the dreaded pitting. Little pits on the back of a chisel can be a royal pain to lap out.
I hope the chisel was one of the newer old Stanley chisels, because the older old Stanley chisels were beautiful tools and worth a fair amount.
R
Yes. Rust comes in orange and black (with lots of browns in-between) depending on the oxidation state of the iron (which sets the ratio between number of iron and oxygen atoms in a rust molecule) and also the hydration state. Heat it, electrolyse it, and you cna convert the reddish sorts to the blackish sorts.
If you go to Clearwell Caves, you can even buy pretty purple "ochre", which is really just purple rust (and not cheap either). It has been mined there as a pigment, since Roman times.
As to your chisel, then just ignore minor pits. Keep them clean, dry, and oiled with a non-staining oil. Ideally keep them polished too, but I certainly wouldn't lap good steel off the back of a decent old chisel, just to shift a trivial pit or two.
If the pits are back from the edge, I agree with you, if they're at the edge, I don't.
What oil do you use on your chisels?
R
Accually there are 2 forms of iron oxide one of which appears black and inhibits further oxidation and one that is orange and promotes further oxidation. Water is not necessary.
ron
snipped-for-privacy@milmac.com (Doug Miller) wrote in news:0JuOg.1222$ snipped-for-privacy@newssvr29.news.prodigy.net:
So does that rust converter stuff remove the hydrated iron oxide leaving only the non-hydrated stuff?
Puckdropper
"Jim Hall"
Once you have a rust spot, it will never re-fill. It will only get larger unless you prevent further rusting - exposure to moisture.
Here in SoCal, its not a huge problem but when I want to protect a tool that sees little use, I will spray it with a mixture of motor oil and kerosene (5 parts oil - 1 part kerosene). Then wipe the excess off and put it away. This may not help in high humidity areas but it works like a champ here. BTW, garden tools get shoved into a bucket of sand mixed with oil before storage in the shed.
Dave
Ummm... actually there are *four* forms of iron oxide.
From the Handbook of Chemistry and Physics: FeO -- black crystals Fe2O3 -- red-brown to black crystals Fe3O4 -- black crystals or red-black powder Fe2O3*xH2O -- red-brown amorphous powder -- that's rust.
Water *is* necessary for rust.
Don't know, sorry. Best to direct that question to the manufacturer.
Yes, I'd agree with that.
My usual bench chisels are Japanese though, so this problem doesn't arise. I could either lap a pit out of the back in a minute or two, or leave it alone if it's in the hollow.
For chisels I use Japanese "camellia" oil, which is actually fish oil with a scent added. Buy it from any quality toolstore, it's common these days. It's persistent, non-oxidising (measurably), non-gummy and lets you go straight into carving lime (basswood) without leaving marks. I also keep a bamboo/cotton waste oil pot full of the stuff on my bench.
For swords I use camellia oil, made from camellias. I get this from a Chinese herbalist, sold as a hair product.
oxidation. Water
So you're saying if i put a piece of metal in a closed container that was evacuated then filled with a high concentration of oxygen it would not rust?
Water can act as a catalyst for rust but so can many other chemicals. Above you seem to define rust as hydrated iron oxide. Generally when someone speaks of rust he is refering to any iron oxide.
That is correct. It would oxidize, but it would not rust.
I doubt that very much. Generally, when people speak of rust, in my experience, they're talking about the red stuff that forms on iron or steel that has gotten wet, never about the black oxidation that forms on iron or steel that has been exposed to air but kept dry.
So the black stuff is just another form of oxide, like rust (red stuff) from metal getting wet and you treat it similarly..? Scotch brite if off and put a sealer, topcoat, camelia oil or other protection on afterwards. Even though it may show up in the same spot weeks or months later, you can slow the deterioration by cleaning off the black and protecting the metal. Does that sound right.? Black rust, man, I never realized oxidation was anything other than red stuff.. Thanks for info..
There's one big difference: the black iron oxide is crystalline and hard. It doesn't flake off under light pressure the way rust does, and if it remains dry, does not contribute materially to deterioration of the metal.
Ever take a look at really old tools? They're nearly black -- but still solid. IMO black iron oxide is more a cosmetic defect than anything else, and doesn't really need to be removed -- as long as you keep it dry. Moisture is the enemy of iron, even water vapor. So.... polish it off if you like, or leave it alone, but definitely put some sort of sealer over it.
Not quite right. If it's black, it isn't rust. Oxidation turns iron black or dark reddish-brown, and is not in and of itself harmful if kept dry. Oxidation plus water makes rust.
Thanks, Doug. That was helpful..
Before the advent of modern chemical bluing, gun barrels were colored by a controlled rusting process leaving the barrel black.
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