I've been getting some mixed results with the acid etching on aluminum. After experimenting for a while, I think I've got a system down. I had photoshop open and I was trying to think of a new design for another enclosure. I was going through some pictures on my hard drive and ended up stylizing a picture of Riki-Oh. For this (and any two tone stuff) I tend to go grayscale, adjust brightness/contrast, use the stamp filter, then do a manual cleanup of any stuff that looks out of place.
I'll try my best to outline the process:
After printing the mirrored image onto a section of PnP blue, I ironed it on. Highest heat, no steam. Strangely enough, when I try ironing on the aluminum, if I don't apply firm pressure right away the PnP "crinkles". I don't know if it's how the aluminum handles heat or what. It actually didn't transfer all that well, but it was nothing a sharpie couldn't fix.
As you can see, you don't really want to use that much of the etchant, just enough to cover the surface. There is no good reason to etch the back and you want to be able to control the process (it IS a chemical reaction).
When the plate is dropped in, the solution should begin to bubble. It reacts a lot different than a copper board. You need to keep a close watch on it since it is an exothermic reaction. Last time I did this (scrambler), I used a diluted solution and didn't keep it in there very long. This time I let it sit for a while with the solution straight from the bottle to try to get a deeper etch. If you leave it alone too long, it will become hot enough to produce vapors, mine did. When I saw it I grabbed it and ran it under cold water to stop the acid. After I rinsed it I dropped it in again and repeated the process about 5 times. I think it became hot enough to remove some of the marker, which is a bummer, but now I know.
Here is the pedal after removing most of the ink resist with some steel wool. Now this is where I left off last time, I liked the look, but I wanted a better contrast on the design. Once it's cleaned up, the design only really shows in the right lighting.
I just took some black acrylic paint that had been sitting in our living room for a while. It seemed to be too thick so I thinned it a bit with some water. I just hit the front with a light coat of the paint in hopes that the resist parts are raised enough that I could remove it without affecting the etched portion. I think a few coats of spraypaint would work well here.
I couldn't find the bit of sandpaper that was floating around my desk so I just used a rough piece of scrap wood to sand the top. I was surprised at how well the etched parts held up, I tried scratching them with my fingernail and it was fine.
I liked the matte finish but I thought it could use a couple of layers of clear coat to protect it. It seemed to really bring out the image, and looks a lot better in person.
I think that if I'm patient enough to get the transfer done well, then touch it up with a few layers of marker, I can make a really sharp looking pedal.
Now that I have a system, I'm looking forward to the next one!