The following is a short description of how I made the acid etched placards for my Staggerwing.
My first plan was to use a laser engraver to remove some aluminum instead of acid. I quickly learned that my low power "engraver" is really just a "marker" as far as aluminum is concerned. Perhaps I didn't have enough power, patience, or knowledge. In any case, I tried a different approach.
I started with a piece of aluminum and sprayed on some Poly-Fiber Aerothane. I let this cure for several days to make sure it would stand up to acid.
I tried three different aluminum alloys. This was not a plan, it is just that I didn't think about the selection when I grabbed a scrap from my pile. The random piece was alclad 2024. The relation between time in the acid and thickness of metal removed was very nonlinear. It eroded very slow to start, then very fast. So the alclad was doing exactly what it was supposed to, protect the more corrosive 2024 from the outside world. Mark that off to relearning another well known fact. I also tried 3003. It erodes very slow. It is close to pure aluminum. I ended up using 6061 bare. I didn't try any other alloys.
The designs were created with PhotoShop. The laser engraver was used to remove the paint where the acid etching was to happen.
The acid mix that I used was two parts 3% hydrogen peroxide and one part 32% hydrochloric acid. A mix I found on the internet somewhere.
An ice bath was used to keep the acid from getting too hot. I tried to use the smallest quantity as possible. The problem with this approach is that the acid can heat up quickly and it loses strength fast. I used a hand held infrared thermometer. I know these are not very accurate, but they can show a trend. If it got up to 90 degrees F, I would pull it out and let the acid cool before continuing. Five to six minutes was the usual time. I tried to remove about 0.003 inches, some of these are not that much. If you have small font, they can get undermined quickly.
After the placards come out of the acid, they were washed, dried and a little MEK used to remove the polyurethane.
In the following photo the top four placards are done with the acid and had the polyurethane removed. The bottom two are ready for the etching.
The placards are then sprayed with flat black lacquer.
The black lacquer is then carefully block sanded off the high areas.
The placards are then trimmed and drilled as necessary.
Some aluminum was painted with Poly-Fiber Aerothane. Allowed to cure for a few days. Then the paint layed is removed in the areas to be etched with a laser engraver.
The part is the etch with the same acid mix given before.
After the etching, the remaining Areothane is removed with a small amount of MEK.
It is then painted. It is ok to paint outside the lines. The next sept is block sanding.
This logo was used on the vertical fin of the early B models. I have seen it on photos up to serial number 83.