I've been wanting to try etching of steel for a while and all the old threads on the subject on this forum didn't exactly help. I finally got around to start experimenting. I chose my AK as the target. This one have seen use but had most of its original finish in place thanks to Autosol (a metal polish/soap that removes oxidation like as by magic - a quick rubdown after use and the blade would be all shiny agian).
After a couple of initial and less than exiting attempts I landed on the following methodology.
Preparations
Application
The resulting finish from an etch like this will differ from blade to blade and depend on numerous factors. Generally the finish will have a smokish gray-brown tone in the softer areas, and a darker, more marked gray-brown color in the hardened area. Depending on light, the color and strength of it, the blade will sort of change in color before your eyes as you move it around. I could have got my etch more even in the non-hardened area, but I was experimenting and it shows.
A couple of shots of my test subject. Difficult to show the finish properly in a still image
The "sweet spot" is partially hidden by reflections a few places, but it is in fact very uniform and stretches almost the entire blade length, stopping only an inch or so from the cho.
Different angle and light. I don't know if i'd call it pretty but probably functional.
Thanks for reading! I am getting my hands on some ferric chloride and will definitely try to etch with it too. Vinegar is cheap though, and if you work patiently and consistently with it you'll get interesting patinas.
Mac
After a couple of initial and less than exiting attempts I landed on the following methodology.
Preparations
- Sanding the polished finish down with ~180 grit and later ~320 grit wet & dry. Carefull to always sand in the same direction to get "even" lines in the metall. You'll want to work out any old nicks and scratches and get a uniform surface. Went pretty easy with the 320grit. Roughening up the finish is essential as it allows the acid to bite deeper and get more hold.
- Degreasing the blade (most if not all dirt should be gone during the sanding, but your fingers are bound to leave some), preferably several times. It needs to be squeaky clean.
Application
- Pour a little white vinegar (I got some 7 %) in a cup. I don't dilute it with any more water and if I had more potent vinegar up to 10-15 % I'd use it straight too.
- Heat the blade under a hot tap.
- Apply the vinegar with a paint brush. Keep applying, if the blade is clean you'll see the vinegar form a uniform "wet" surface. Brush back and forth in the same direction you sanded the blade earlier on and try to keep the vinegar coating as even as you can, remember to work both sides of the blade! If you see spots, streaks or similar form, work the area with the brush to smooth it out. Add more vinegar with the brush regularly. If you've done things right and everything works you'll quickly see a fairly even satin-silver/brownish hue start to form with a distinct hardened area taking a different tone. You can keep doing this for 10-20 minutes.
- Use something to neutralize the acid, I just drip generous amounts of normal liquid dishwashing soap and rub it into the whole blade. Rinse off under the tap. Apply more dishwashing soap and use #0000 steel wool to scrub the blade down. This will remove loose oxidation and polish the blade. A little known fact is that many cleaning products (soaps, even toothpaste) are basically very mild polish/abrasives as they by nature have fine particles in them. Don't overdo the scrubbing, you'll want to etch at least three times and if you scrubb too hard and much you'll polish the blade
You'll want to keep the blade slightly rough for the next etching to bite properly. Over time with several etchings and rubbdowns the steel with get something similar to a brushed and then polished stainless steel surface, only obviously darker due to the etching. - Rub the blade in with mineral oil, Ballistol, whatever you like. Rub the oil off with a cloth or paper towel. Repeat. This sort of cleans the blade and removes a little bit more oxidation. You don't have to do this between each etching but you will have to at least put some oil on it when you're finished etching because it'll be very clean and oxidize (rust) easily. You'll note that the oil will "take" better on the blade than when it was new and polished.
The resulting finish from an etch like this will differ from blade to blade and depend on numerous factors. Generally the finish will have a smokish gray-brown tone in the softer areas, and a darker, more marked gray-brown color in the hardened area. Depending on light, the color and strength of it, the blade will sort of change in color before your eyes as you move it around. I could have got my etch more even in the non-hardened area, but I was experimenting and it shows.
A couple of shots of my test subject. Difficult to show the finish properly in a still image
The "sweet spot" is partially hidden by reflections a few places, but it is in fact very uniform and stretches almost the entire blade length, stopping only an inch or so from the cho.
Different angle and light. I don't know if i'd call it pretty but probably functional.
Thanks for reading! I am getting my hands on some ferric chloride and will definitely try to etch with it too. Vinegar is cheap though, and if you work patiently and consistently with it you'll get interesting patinas.
Mac
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I etch a lot of mine just because.
I've found something that's marketed here as a polishing cream, another that's supposed to being a polishing agent with wax mixed in it - a 2 in 1 type thing. 
