removing scale from forged knife?

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Railrider1920

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Hey Folks,
I have a knife I have been forging on. I want to do some file work on it now. I was told to get the scale off of it first. To do this, I was told to soak it in muratic acid for about 20 minutes. Looking at some search results here, someone suggested vinegar over night. So which would you use?

If you would use the muratic acid, what is a good ratio acid to water to mix up a batch? The instructions suggest very little acid to the water. Then just add a little more acid to the water until the concrete starts to bubble. (cleaning concrete)

If I use the acid, can I wrap a piece of copper wire to the blade to lower and raise it into and out of the acid? If not copper, stainless steel wire ok? I'll have it in a PVC tube with caps.
Thanks
 
Have always used it undiluted. Don't store it in your shop, the tube will not keep it from escaping and rusting everything. I'd use stainless wire.

I've never soaked a knife in anything to remove scale, I've always just ground it off.
 
Just use vinegar... it works overnight and is harmless. Don't mess around with dangerous acids until you truly need to.
 
Call me impatient or what ever you like. I have never soaked in anything over night befor filling. The trick is to get the scale off and the hardened metal just under it. I use a some emery clothe 50mm wide rolls or what ever I have on hand. Once you have the scale off the file will not be damaged. If you make a batch by all means do a soak or even if you have the patience that I don't. But you don't have to if you don't want.

I had a mate who used a tub of old cut lemons and water to etch clean old rusty metal.

STAY HAPPY
REG
 
Don't use copper wire or copper based alloys. Use plain steel wire or some kind of string. Copper will go into solution, contaminate the acid and plate your blade with copper. I'd steer clear of muriatic acid. It fumes a lot and eats at the steel. You can boil it in vinegar, which is quicker, but do it outside because of fumes. It will also eat at the steel. A jewelers pickling compound will also work and doesn't tend to fume and eat at the steel as much.

I usually just use a Dremel with a little grind stone bit.
 
Thanks guys. I would rather grind on it, but don't have any type of grinder yet so I'm stuck with files. I'll get out my bottle of vinegar and see what it'll do. Putting it into the acid with some copper wire sounds interesting. I may have to try that one day. I'm glad you mentioned that Tai.
Thanks guys
 
birdog4 said:
sodium bisulfate.... the stuuf ya put in the toilet to remove rust
Click to expand...
:thumbup:

Just go to your local hardware/dept store and get the Ph balancer used in pools and hot tubs, sodium bisulfate. You can get it cheap, I get a big jug of crystal powder for around $9, it is much safer, doesn't fume like pure acids, and will peal even borax scale off in a few hours. You can even leave your blades in the solution over night if you like. This is the chemical that industry uses to pickle steel and handle these issues. Don Fogg was onto this some time ago and most likely due to this we had it at the New England School of Metalworking for my intro class last week, it allowed the students to grind perfectly clean blades and save enormously on belts.
 
birdod4 and Kevin, thanks for the additional info. Maybe I'll try that next time. I soaked it in vinegar yesterday and it worked great. Just a few small spots where it didn't come off. Now I just have to get out the files and maybe the belt sander.

Edited to add: Is the left over vinegar now useless or will it work on the the next forged item?
 
Railrider,

The vinegar will work for a whole lot of blades, don't throw it out! It also works fastest warm, but avoid boiling as it get's the bad fumes. Best of luck.
 
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