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Removing Patina (dark color) after heating steel


Nathan Stanford

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I recently forged a knife from a wrench.  I want to have a shiny finish but I can't figure out how to remove the dark color on the handle section.  Not sure what is called but I just know it's the color you get after heating the metal in a forge.  I can't sand it and buffing has not worked.  Looking for some advice.

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A picture might help us a bit here. 

You say you forged a knife from a wrench. You don't say whether you hardened (quenched) the blade after forging or tempered it after that.  If you did not then the steel won't be as hard as preferred for a good blade.  The reason I bring that up is all those things can add/change the surface color on the steel, and there's no point in trying to get shiny until you're done with all those things.

If the color is what I think you are referring to, it's oxidation of the steel on the outer layer, and the colors correspond to the temperature the steel reached.  It's normally a very thin layer that is worn off fairly easily.  Why can't you sand it?  Sanding with successively higher grits until you reach 2000 to 3000 grit paper followed by a buffer gives close to a mirror finish.  It doesn't get much shinier than that.

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I have not gone ahead and heat treated it (quench or temper).  I should say I don't want to sand it bc I want to preserve the wrench look in the handle. Not really going for mirror just not such a huge contrast in color between the blade and handle.  This is the third knife I have made.  I'm a noob having a good time trying to absorb all I can.  Here is a picture of my work in progress.  Thanks in advance for any assistance. 

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Have you tried a wire wheel on a grinder?

If that doesn't work, then maybe try soaking in vinegar for a day.  If it's scale from forging that you are dealing with then that will dissolve/loosen the scale and help you get down to the bright metal. If you do that just make sure that you rinse it well, then neutralize it with a baking soda solution, then rinse again and dry.  Vinegar will make it rust quickly in the open air otherwise. A wire wheel should help get any remaining spots at that point.  You have a lot of edges to catch on a wheel though, so please make sure you don't let it turn into a projectile weapon.

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A 24 hour soak in regular household vinegar might eat that scale off. Scrub it with steel wool to clean the gunk off after then spray with Windex to neutralize. Then you can wire wheel/buff from there to get a little more shine. These are a before and after of a tomahawk I'm working on after just the vinegar bath and steel wool scrub.

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I'd do it before.   If you quench in oil you'll still end up with a black-ish layer on the steel that you'll need to clean off, but it tends to be not quite as stubborn as forging scale.  Tempering properly will also change the color of the steel.  For blades we're usually looking at a straw or slightly darker color.  This can usually be stripped off with something like steel wool though.  Another note though, a vinegar bath will turn shiny steel into a bit of a dull grey color.  It's not that hard to shine it up again, but you won't keep a shiny finish in a vinegar bath unless you protect it with something impervious to vinegar.  Black electricians tape might work, but I haven't tried it personally.

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Note you do NOT need to heat the handle to glowing and quench in oil; just the blade.  Drawing temper on the whole item is OK though.  (no need to bake on an oil finish that you then have to remove from the handle)

Have you thought to get a basic how to make knives book like Steve, our curmudgeonly Moderator has written: "introduction to Knifemaking" 

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I only heated the handle to straighten the little bend that is at the end of all box end wrenches.  It most definitely won't get quenched.  I have not gotten any books on how to make knives.  I'm sure many people on this forum will not like to hear that most all of the info i have gotten has been off of the net (youtube videos, forums, pinterest).  I dont have a lot of money so this is my best resource.  I will look into this book as I am starting to get a bit serious about this little hobby (hence joining a forging site).  I recently went from a plaster of paris/sand mix refractory in a coffee can forge to a bit larger can with ceramic insulation thank goodness for Christmas bc that insulation is not cheap. Lol

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Actually stuff like kaowool is cheap compared to wasted fuel costs. I often boggle at people basically telling us that they couldn't afford $20 of kaowool but were OK with spending an extra US$100 in fuel by not using it.  It can also be sourced free or cheap if you are lucky and willing to work at finding it.  Places that work on large commercial boilers may have scraps that would do for a forge for instance.

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There is a section  on this site called forges. There are some pretty knowledgable people that have gave a lot of time explaining  the how and why  of forges and burners. There is also a knife making classes section again  lots of contributions by knowledgable people . Pull up a chair get your favorite  beverage  and read . A lot of your questions  will be answered. 

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Welcome aboard Nathan, glad to have you. If you'll put your general location in the header you might be surprised how many of the Iforge gang live within visiting distance. 

Did you strip the chrome plating off the wrench before making a blade out of it? Chrome plating is toxic if heated in a forge so don't do it. The black patina formed by getting chrome hot is hard to get off. 

You're close enough to a public library to check out books yes? There are a lot of high end blacksmithing books in the library and if your branch doesn't have a copy ask them to ILL a copy for you. There are a number of excellent publications about blacksmithing and heck most shop skills available for free download online. The "Cosira series" is one that comes to mind. 

I'd like to recommend you wipe some oil on what you've made and put it up for now and start picking up the blacksmith's craft. Once you've earned proficiency at the anvil learning to forge blades is MUCH easier and you'll waste a whole lot less time making expensive and labor intensive mistakes.

Most importantly though, STOP messing around forging chromed wrenches!

Frosty The Lucky.

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Just added my location to my profile.  It was not chrome plated.  Not messing around with that. Lol.  I have been trying some other stuff with my forge than just the knives.  Made some split crosses, stuff from nails, necklace for my wife with forks, and just recently made my own tongs.  I was thinking about this the other day and was looking online for ideas to step back and find some small projects where I can focus on moving the steel in different ways.  I have found a kind of zen working with metal.  I'm not out to make swords, just things that others cannot.  I'm really glad that I joined this site bc everyone seems so knowledgeable and ready to assist others. 

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You know about chrome, good. Yes, blacksmithing is very zen like on so many levels it's hard to describe. I often meditate in 2,000f steel, it's gooooood. 

This project shows pretty good hammer control and understanding of how steel moves under the hammer. I'd say you have a natural knack for the craft and a good eye. How about pics of some of your other pieces? We LOVE pics you know. :)

I see you guys didn't lag crossing this thread into punnishment.

Frosty The Lucky.

 

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Well like I said I'm a noob but here is a picture of the first knife I made.  The steel is from a really old ladder (the straps that prevent over extension)  it is ground not forged hidden tang (walnut).  I learned that hidden tangs are a bit tricky for a beginner. The welded guard is just decor covering my failed attempt at fitting a guard correctly. Lol the sheath was done for me by my wife's grandpa.  Will post a few more on my next break.

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Here's my second knife.  I use scrap got my projects bc I am just learning.  Story on this one is that I forged it out of the steel backing on a brake pad.  I had just changed brakes on a friend's car, knocked the pad material off of it.  Then said wth and the it into my forge.  Seems fairly successful.  Holds an edge. Handle is walnut sandwiched between pine.  First attempt at pinning as well.

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Here are some random projects too.  Couple of split crosses, a cat I welded for my wife, my own tongs, another picture of my brake knife in the making.

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  • 4 years later...
On 1/9/2017 at 3:55 PM, Nathan Stanford said:

I recently forged a knife from a wrench.  I want to have a shiny finish but I can't figure out how to remove the dark color on the handle section.  Not sure what is called but I just know it's the color you get after heating the metal in a forge.  I can't sand it and buffing has not worked.  Looking for some advice.

I personally use a wire wheel on my angle grinder. (This probably doesn't help much as it is 4 years later but I figured I'd throw it out there)

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