Blackening a blade with AC electrolysis?

[Gaznazdiak]

I have just finished the surprisingly simple job of building my own AC/DC etcher/marker machine (gotta love that ewe-choob).

The ease with which this and some saturated saline can put a deep black, permanent mark on steel leads me to the question, can this AC/Saline method be used, on a larger scale, to blacken an entire blade?

My thought was, if it works on small scale to blacken an etched logo, would submerging the whole blade in the saline work with my 12V 1A AC power source?

Anyone tried this?

I have searched here and the web to no avail.

[Chris Williams]

First, the following applies to DC only! You can easily kill yourself mixing AC and a conductive fluid. On that note, DC isn't harmless and I do not know what design you are using; make sure you cannot be part of the circuit. 

If you want to immerse the workpiece in the solution, place the workpiece (attached as a cathode) in a shallow container with electrolyte and instead of holding a q-tip (or whatever your design uses) with the anode, you would use a nail or similar to "paint" your workpiece. How much etching you get has to do with the current density at a given point and the dwell time. Even though I said "paint," you shouldn't actually touch the workpiece, but rather keep the tip of the anode a fixed distance from the workpiece as you move it. You can make up for slightly uneven anode distance with the time you linger in each place. 

If you just immerse an anode and cathode (workpiece), the etch won't be even (due to the varying current density of different distances and geometric features), but a flat plate placed parallel to the blade may be a close-enough approximation of your knife blade to serve as a "conformal" anode. You can use nail polish or similar to protect the very edge, as it will have a relatively large current density and etch faster than other places. Agitation of the electrolyte will help to get a more even etch. 

You could also just use a larger swab and etch the entire surface with the swab and without immersing the workpiece. You will likely need to refresh the electrolyte on the swab a few/several times while etching. 

[Frosty]

Search "Electro Polishing" for the same technique used to polish rather than tarnish.

Frosty The Lucky.

[Gaznazdiak]

 

Chris

The mains 240V 10A AC is "stepped down" to 12V 1A AC by a store bought transformer before it enters the machine, then a 3 position switch sends it to my marking leads from one side and via a bridge rectifier to my etching leads from the other.

I deliberately built it with the lowest current that will still do the job, for safety reasons, what I'm wondering is whether 1A is too low for immersion to work.

I have tried using a bigger pad on the anode, but that leaves an inconsistent finish, hence the question.

It's looking like I need to build another rig, something stand-alone that I can set the blade into so that the process is "hands off".

Thanks for the tip about protecting the edge, density was something I hadn't considered.

Frosty

I will do that today.

I've done more reading and watching than actual knife making since I decided try to make a go of it last year.

No point wasting time and materials buggering about in ignorance, plus, once you stop learning, it's time for the dirt nap.

Thanks guys.

[Chris Williams]

It's been a while since I did any of this, and I don't remember the Amps I was using. I was also using oxalic acid to etch stainless, so it wouldn't be directly comparable to your setup. All I can say is try it and see. As long as you are getting some etching, then using immersion with a low current would work; you'll just have to determine an appropriate time. You will probably need to rotate the knife 180 degrees halfway through to get an even etch on both sides. If you don't have a large volume of electrolyte, or if you don't agitate it during the etching, then you may not get an even etch rate over time, which would complicate trying to time the process for consistency. 

[Gaznazdiak]

I've had as much fun building the tools I need as I have experimenting with the forge and my new 2x82" grinder.

I built myself a little blade and edge scriber this week as well, out of some scrap square tube, brass rod, a broken drill bit and, believe it or not, a T shaped piece of bronze that was apparently part of a WW2 torpedo, works like a charm.

It's too wet and windy here to shoot at the moment (my other hobby is murdering ferals at long range) so all the tinkering helps keep the dreaded boredom at bay.

[Gaznazdiak]

Well, in my search for a simple way to blacken a blade I discovered something even better.

How to achieve the same effect as ferric chloride with simple white vinegar.

Xxxx  I love ewe-choob.

https://youtu.be/DRtEPDzCa2A