Brut de forge finishing discussion

T

Tokoloshe

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Mar 13, 2022
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8
Hello everyone,

I'm currently finishing up my first brut de forge knife and have some questions about the best practices for finishing the unsanded, forged area. I've noticed that techniques vary significantly among knife makers, and I'd like to understand the benefits and drawbacks of different methods.

For instance, Japanese chef knives often feature a kuro-uchi finish, but even within this category, there are variations. Some makers leave the blackened forge scale intact, while others may clean it up a bit.

In the U.S., I've seen a wide range of approaches. Some makers leave the forge scale and even spine untouched, while others use a wire wheel or sandblasting to remove it. Additionally, I've come across instances where makers apply a cold bluing process to darken the forged area.

I'd love to hear your experiences and preferences. What are the advantages and disadvantages of these different finishing methods? Any insights or tips would be greatly appreciated!

Thanks,

T.
 
Several techniques will work:
After the forging and normal cycling, but before HT -
1) Forge it, clean it up, leave the scale as-is.
2) Forge it, clean it up, soak overnight in pickle (PH-down solution), neutralize, scrub well, FC etch.
3) Forge it, clean up, short soak in pickle, neutralize, wire brush on a bench grinder or with an angle grinder.
4) Do #3 then buff with black rouge.
5) Do #2 and scrub with 200 grit SC powder slurry, etch with FC.

Any combo of the above will usually work.

I don't like it left "unfinished". I like the area rough forged buy cleaned up and somewhat smoothed
 
I prefer wire brushing forge scale heavily or removing the heavy scale with an overnight soak in PH down then wire brushing. For kitchen knives specifically rust can be a big concern so the smoother the forged finish the better. A lot of Kurouchi finishes are painted on coatings versus the actual forge scale.
 
Stacy and Josh,

Thank you for your prompt and thorough responses.

Excuse my ignorance but what is "pickle (PH-down solution)?"

Thanks in advance.

T
 
"Pickle" is a term used to describe an acid solution. In metals it is a solution to remove scale. The steel you receive from the supplier was pickled to make it look good.

When working on steel the surface gets covered with ion oxide and other oxides. The pickle dissolves/softens this, and it can be scrubbed away.

The most common pickle used for knifemakers and jewelers is Sodium Bi-sulfate, NaHSO4, commonly available at the hardware store, pool supply, or online as "Ph-Down". You mix one or two cups in a gallon of water, Stroe it in a glass or plastic container when not in use.
 
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I've just been wire brushing them. I also like the organic texture created by leaving the spine untouched
I think it's going to depend a lot on exactly how clean a forging you can do. You can do all this after you've ground the bevels, they'll just need a quick polish to brighten them up (or not, if you want a forced patina)

Stacy E. Apelt - Bladesmith said:
The most common pickle used for knifemakers and jewelers is Sodium Bi-sulfate, H2SO4,
Click to expand...
Isn't sodium Bi-sulfate is NaHSO4, and H2SO4 just sulfuric acid?
 
Thanks, fast typing error ... brain going slower than the fingers. You are of course correct. I edited it.

You get NaHSO4 by reacting NaOH (lye) with H2SO4 (battery acid). It is called an acid salt and is different from neutral salts like NaCl. (NaOH + HCl = NaCl + H2O)
It is a Bi-sulfate because it retains the original sulfate compound in the new compound. Technically, it is both sulfuric acid and sodium sulfate
 
Not all things called pH Down are based on sodium sulfate. At least two MSDSs I googled were based on phosphoric acid. Google "ph Down MSDS" to understand. Won't really matter in this case, but good to know what you're dealing with. Surprising how multiple, different products bear the same name.
 
Thank you all for the clarification. I truly appreciate it.

Could you please elaborate on the benefits or disadvantages of the various techniques or are they simply stylistic choices?

After the forging and normal cycling, but before HT -
1) Forge it, clean it up, leave the scale as-is.
2) Forge it, clean it up, soak overnight in pickle (PH-down solution), neutralize, scrub well, FC etch.
3) Forge it, clean up, short soak in pickle, neutralize, wire brush on a bench grinder or with an angle grinder.
4) Do #3 then buff with black rouge.
5) Do #2 and scrub with 200 grit SC powder slurry, etch with FC.

Thank you in advance,

T
 
Tokoloshe said:
Thank you all for the clarification. I truly appreciate it.

Could you please elaborate on the benefits or disadvantages of the various techniques or are they simply stylistic choices?

After the forging and normal cycling, but before HT -
1) Forge it, clean it up, leave the scale as-is.
2) Forge it, clean it up, soak overnight in pickle (PH-down solution), neutralize, scrub well, FC etch.
3) Forge it, clean up, short soak in pickle, neutralize, wire brush on a bench grinder or with an angle grinder.
4) Do #3 then buff with black rouge.
5) Do #2 and scrub with 200 grit SC powder slurry, etch with FC.

Thank you in advance,

T
Click to expand...
All of those will provide an "acceptable" finish and the aesthetics combined with the intended purpose of your piece, should drive your decision. :thumbsup:
 
Yeah, it's an aesthetic choice. What approach you like will depend on why you are doing it and what you're interested in
 
As the others pointed out, the use of the knife and your personal aesthetics will determine what you need to do.

1) Forge it, clean it up, leave the scale as-is.
Advantage - This is very primitive look, takes no extra steps, and used for a rustic look. Disadvantage - It is an unfinished surface that may rust and isn't food safe.

2) Forge it, clean it up, soak overnight in pickle (PH-down solution), neutralize, scrub well, FC etch.
This is a cleaner version of #1. It will have a dark surface.

3) Forge it, clean up, short soak in pickle, neutralize, wire brush on a bench grinder or with an angle grinder.
Advantage - This gives the most rustic look and is food safe. Disadvantage - It is still prone to rust.
It is the most popular method of getting a forged finish that looks clean. You can also etch in FC after the brushing to get a darker surface.

4) Do #3 then buff with black rouge.
Advantage - This is a shinier version of #3.

5) Do #2 and scrub with 200 grit SC powder slurry, etch with FC.
Advantage - This is matte version of #3

I do #2,3,4 mostly.

most often.
As to Fitzo's comment about phosphoric acid used as Ph Down - Phosphoric acid is used as a Ph reducer in hydroponics because it is a source of phosphorus, which helps plants grow. Most swimming pools are Ph balanced with Sodium Bisulfate.
It is used as a steel pickle in industry. It not only removes the scale but leaves a black oxide coating. It is why it is in many "Rust Removers" used on wrought Iron rails and outdoor furniture.
I don't think it comes as a powder. Phosphoric acid is used to give a "blacksmith finish" to things in industry. The black oxide is somewhat rust preventative. Knives and guns are often "parkerized", which is a process using phosphoric acid.
It costs a lot more than Sodium Bisulfate. It is also a bit more dangerous to use.
 
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Stacy et al.,

Thanks for the responses. I truly appreciate your help understanding a new topic to me.

Cheers,

T
 
Since i got curious and checked; the solid form of phosphoric acid melts at quite a low temperature, especially when it's absorbed water. So i guess it wouldn't be practical to transport as a dry powder.

As Stacy pointed out elsewhere you can also use trisodium phosphate as the neturalising solution if you want the formation of the iron phosphate which is tougher than the iron oxide
 
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