Johnny has a bit of an unorthodox methodology. We've spoke about it, and it works for him.
What's cool is that everyone has so many different though processes and it all looks different.
Here's how I do it (if you really want to know, you can watch my hour plus tutorial).
I grab the following sand paper and a electric sander. I ONLY hand sand with the last bit. Fuck that shit. I use 250, 600, 800 and 1500 grit paper in that order. The 250 takes the top off so that you can get down to the less shitty aluminum (which in some cases is not true. Sometimes you buy boxes and they already look sanded and you can ignored this step). I dry sand with 250 and the rest I wet sand with. I load my hand sander with each. Put a little water on the enclosure and sand to my preference. You want to try and keep it even though or else the trasfer will look like shit. For the 1500 grit (sometimes I'll skip this if I'm out), I hand sand under water in the sink. It gives it a nice shine. If I'm feeling extremely meticulous, I'll even try to give it a semi polished look.
Cleaning the enclosures. This is the single most important step IMO. If it's not clean enough that fucking transfer will not go on right. So I do it in steps. First I rinse it off. Then I use acetone to clean off any grit. Next I use baby dish washing soap. It's the stuff they make for baby bottles. I've found it's extremely effective with pulling grit. Then I use alcohol or acetone again until the paper towel I'm using has no dirt left on it.
Preparing the box afterwards. If you don't want to paint the sides and leave them bare, you can use painters tape or duct tape. Just so it seals them and makes sure the acid can't hit the surface. Spraying them is the easiest, but in my experience you'll want an automotive paint for this. It stays better, looks better and can take the heat of the acid better.
For the transfer. Fuck all the papers. I hate them all right now. The Dollar Tree made the best and they stopped producing it. It all sucks now IMO and I hate it. In a pinch though, one of these fellas might be able to suggest something. Anyway, you need to use a inkjet paper with a laser printer. There's a chemical reaction that occurs when you print that makes the ink sit more on the surface. This also you to transfer it from A to B.
Using an iron. Make sure to get one where you can turn the steam OFF. You do not want steam on. The setting I've found that works best is the one for linens. It's going to take some trial and error to figure out what works for you. I'll leave you to watch some videos to see how exactly to do this, but it's simple. NOTE. I usually heat the enclosure prior to the transfer. I've found this helps with the entire process. 30 seconds is usually more than sufficient. For taking the transfer off, I let them cool first, but some papers work better if you pull them hot. This might be a trial and error thing as well. You most likely will have to fill in some negative space that the iron didn't get onto the enclosure. I'd recommend an enamel paint pen over anything else. You can get precise that way.
The etchant. Acid Magic works great. I shouldn't have told everyone about it either.
Now everyone uses it!!! LOL!!! It's cheap and you can etch a box in under a minute. You have to be careful though. If it gets super heated, it will exploded. I had some get too hot the other day and forgot eye wear and that shit literally hit me on the white of my eye. Had it been any other form of acid, I'd have a hole in my fucking head. So be careful. It's 90% less toxic that muratic acid, but you would be well advised to still wear a respirator (it can knock you out).
After etching, place the enclosure in water for 2 minutes. This will fully neutralize the acid. I usually run it under a sink but a bucket will do the same.
Removing the transfer. Use acetone. It will create a crisp and awesome look. Wear gloves though. Believe it or not that shit is toxic as fuck. Also, I'd advise the respirator. Don't get lazy like me and ignore most of this shit.
Painting....I don't really do it that much, but when I do, I like to get abstract with it a bit. I use translucent paints that are used for model cars. It works well and stays. Or I sometimes use paint pens. I don't fill in the entire areas though because I like my etches kind of gritty looking. Even with blemishes.
Clear coating is a MUST. If you want your etch to look good for years, don't skip the clear coat. It will ensure the enclosure does not corrode over the year and stay looking fresh. If you use enamel paints, just we wary that some of the crummy kinds actually tend to coat better. I don't know why. You're technically not supposed to clear coat enamel. Zero fucks given. Light coat it several times. If you go to heavy, it can melt the paint. It sucks. You can also you a clear coat epoxy. I did this for some enclosures for Industrialetric and it looks bomb! It literally coats the etch in armor and looks crazy good! It's an absolute bitch to work with and is expensive, but it's well worth it.
Above all, take your time with this stuff. Learn your method before you try to cut corners. Once you get really good at it, you'll figure out ways to do things faster.