Black. Black as my heart.

September 5, 2006 9:26 AM

Oh god no, please help me if you know /anything/ about steel. I have ruined my sword.

I have a sword, custom built (not terribly expensive, chinese forged steel, but I love it), for iaido, and, having forgotten to clean it last time I used it, I noticed a little bit of rust on the blade. I went to a shop and asked for a product that removed rust. I got HG (Hagesan) rust remover. I was told it would not damage the steel. I cleaned the sword with it and left the product on for about 10 minutes (the flask said "leave on for anywhere between 10 minutes and a few days), then rinsed as it said on the flask and now the blade has turned blackish/rainbowy. The flask says the product contains phosphoric acid. How do I fix this?

posted by Skyanth to grab bag (11 answers total)

I would ask over at Blade Forums.
posted by callmejay at 9:32 AM on September 5, 2006

callmejay,
Well played. That is a great link for the question.
posted by JohnnyGunn at 9:36 AM on September 5, 2006

Triple 0 steel wool and elbow grease.
posted by hortense at 9:37 AM on September 5, 2006

Thanks, posted the question over there as well (and in doing so I think broke the record of fastest registration for a forum ever), but I would still like to hear from people here.
posted by Skyanth at 9:38 AM on September 5, 2006

Sounds like a bit of oxidation. I would try some brasso, buffing with the 000 steel wool as mentioned above.
posted by deadmessenger at 9:49 AM on September 5, 2006

What was the finish like before you put the blackening agent on? If it was not a mirror-finish, I'd use Scotch-Brite pads, which work better than steel wool. if it was mirror-finished, I'd use the finest grade of Scotch-Brite, then a metal polishing compound.
posted by Kirth Gerson at 9:54 AM on September 5, 2006

I wouldn't use anything terribly abrasive. Bartender's Friend or Cameo Cleaner, both for stainless steel, do remove discolorations from stainless without a lot of scrubbing. Also Maas polish (just a little dab on a soft cloth) will polish out things. Get it in the tube.
posted by LeisureGuy at 11:15 AM on September 5, 2006

Phosphoric acid does more than 'discolor' steel. Cleaners are not going to restore the original finish. Also, the sword is apparently steel, not stainless.
posted by Kirth Gerson at 1:50 PM on September 5, 2006

You could get a blueing agent from a gunsmith ($6-12) and use it to take the blade the rest of the way - to completely black.

It might be taken as RealUltimatePower taste though?
posted by -harlequin- at 2:05 PM on September 5, 2006

Phosphoric acid is the main ingredient in "naval jelly" and a lot of "rust converters", and as such it is sometimes advertised to "turn rust into a durable black finish". The wikipedia link above says it can be scrubbed off. I might try zud or just buffing it out on a buffing wheel with polishing compound.
posted by 445supermag at 2:08 PM on September 5, 2006

As 445supermag says, Phosphoric acid is the primary tool of choice for car restorers to get rid of rust (used in products like POR-15 or Rust Mort). It converts the cancerous iron oxide into inert zinc phosphate, but in the process turns the affected areas (i.e., any part that used to be rust) into grey or black.

The problem is, once the metal is gone, it's gone. There's nothing you can do to get it back. So, whether the "gone" metal is rust or inert black phosphate, it's still just a placeholder for good metal gone bye-bye. The other thing is, your sword is not "protected" now. This is a common mistake people make when buying into the marketing hype for some of these products—they think that "now that I've applied this stuff, the metal is invincible to all future rust." It's still most certainly vulnerable. If you regularly leave steel in adverse environmental conditions, pretty-much the only thing you can do is coat it in a thin sheath of oil.

As to what you can do about it—basically, you can grind down the blade until you hit good metal, and polish it back up by hand. That's about it.
posted by Civil_Disobedient at 7:02 PM on September 5, 2006