I have a Cold Steel Kukri machete that I've used for a few years. It was for rough tasks, like cutting sod, that I wouldn't use nicer edged tools. It's not very obvious below but the original finish was getting worn off and the sheath fasteners had began to rust. It rolled around in my trunk for a few years, so I'm not shocked or disappointed.
The kukri is made out of 1055 Carbon Steel, so I'd decided to use it as a test subject for acid etching instead of applying a new finish. The first step was to remove the original finish with a belt sander (being careful to not overheat it and ruin the temper). Then I applied thick nail polish to the areas I did not want the acid to affect. To make it dorky, I decided to use Anglo-saxon ruins for my initials.
At the local hackerspace I experimented with scrap washers with different HCl concentrations. The washers were an imperfect test because often they had different surface treatments than raw carbon steel, but they were what I had. I began with some 10 mol / ~32% HCL in 15 minute periods. At higher concentrations the nail polish actually flakes off and ruins the pattern. Eventually I settled on a 10% solution, which is a 1 part water to 1 part Muriatic Acid. Note that I had to dig around the MSDS to figure out the concentration.
I used a glass vase to hold the solution and set it in a spare slop sink we had laying around (there's a lot of things laying around the shop). It sat for one hour at 10%. If you wanted deeper etching, my understanding is you would wipe off the surface layer and re-apply the etch to make it deeper. I only wanted a cosmetic etch, so I only used the single application.
After that I just rubbed off the nail polish with acetone to reveal the final pattern. I did use a buffing wheel and some Renaissance wax for the final finish. If you don't do a heavy etch, be careful to not over-buff it and remove some of the effect.
Honestly, it's not as nice as I had hoped. Had I spent more time on the pattern or had some other 1055/carbon steel samples I could probably have dialed it in more. That said, this is a $25 machete. Now it's now customized and I have experience in a new skill. Before applying the treatment to a DIY knife, I'll be doing some more forum research.