Etching 15n20

Bühlmann

Bühlmann

North Lake Forge
Joined
Jan 6, 2022
Messages
475
What’s the best way to darken 15n20? I know it’s meant to stay bright with its Ni content in pattern welded applications, but if used as a mono-steel blade is it possible for the flats be effectively darkened to contrast the bevels? I tried some cold blue and it came out pretty blotchy & irregular. Is this just the nature of the material, or is there a better way?
 
I'm glad Hoss confirmed it. I haven't worked with 15n20, but I used ferric to blacken 3V when cold blue wouldn't even touch it.
 
This is what my 15n20 looks like after 12 hrs in undiluted ferric chloride:

9A0D0116-01E5-4DE0-B66D-805823BE91D2.jpeg

Nice matte silver finish, but not dark. Going to see if some coffee will darken it up.
 
Eric, citric acid may do something because its ability to complex metal ions sometimes produces unexpected results, but unlikely. I am afraid you are going to have to go to a strong acid (ferric chloride is an acidic salt of hydrochloric acid, and nowhere near as "strong"). Thus, I would recommend you try muriatic acid, aka "brick cleaner" or "commercial grade hydrochloric acid." Mandatory disclaimer: WEAR PROPER SAFETY EQUIPMENT. Also, don't keep it in the shop or house. Hydrochloric acid gas gets through every cap I've encountered. It will slowly rust all the tools in your shop.
 
Thanks Mike. I tried some muriatic acid briefly last night, but only for a short period, say 10 min or so, and it looked no different than the ferric chloride. I can try it again though, maybe overnight? I think I'll try some lime or lemon juice first. Much nicer to work with!

I have the coupon soaking in instant coffee sludge right now, warmed to "too hot to touch, but not boiling" on the stove top. It's darkening a bit. Here it is after about 2 hrs:

IMG_0507.jpg
 
Eric, does it mention the concentration of the acid in your bottle? Sorry, I thought the commercial stuff would etch this nickel steel. I know that concentrated lab reagent will etch both L6 and 15n20, but where to get the full strength stuff? Nitric acid will likely etch it, also, as that's what's used to passivate stainless steel, but that's even less likely to find readily.

I've never tried coffee "etching" but have read that it is little more than a surface dye. Does it scrub off easily?
 
fitzo said:
Eric, does it mention the concentration of the acid in your bottle? Sorry, I thought the commercial stuff would etch this nickel steel. I know that concentrated lab reagent will etch both L6 and 15n20, but where to get the full strength stuff? Nitric acid will likely etch it, also, as that's what's used to passivate stainless steel, but that's even less likely to find readily.

I've never tried coffee "etching" but have read that it is little more than a surface dye. Does it scrub off easily?
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SDS from MG Chemicals says 38-42%.

The coffee etch doesn't appear to be too durable.

There's a "nitric acid substitute" by JSP on Amazon. Maybe I'll order some of that and give it a try.
 
That stuff says "2TSP per 90ml of hydrochloric acid". That makes aqua regia (HNO3 nitric acid + HCl hydrochloric acid), which dissolves gold. Mix that with some of your muriatic acid and it should ought to do something. Good luck. Be careful about fumes and spills. Nasty stuff.
 
Bühlmann said:
This is what my 15n20 looks like after 12 hrs in undiluted ferric chloride:

View attachment 1951410

Nice matte silver finish, but not dark. Going to see if some coffee will darken it up.
Click to expand...
You need to dilute your ferric, undiluted it won’t etch well or give a dark finish. It works better diluted with either water or vinegar. I use a 50/50 mix of ferric and vinegar, I’ve seen people using mixes similar to that or up to 1 part ferric to 10-12 parts water.
 
Thanks Joshua, I'll do that when I get back home. I just tried a sample coupon to see if it would work with a little bit from the bottle I purchased. Seems counter-intuitive that it would be less reactive in a higher concentration, but I'm not doubting you. Maybe it creates more reactive ions when added with water? Been a looooooong time since I took a chemistry class!

I know I'm trying to darken a nickel-containing steel that is meant to resist acids, but I'm learning and trying to see what I can and can't do with what I have available. I appreciate everyone's input.
 
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