I needed an escutcheon for the keyhole, and I couldn't find one I liked so I decided to make one by etching a design on sheet brass.
The first picture is the setup for etching: protective equipment (gloves and eye protection); ferric chloride etchant; disposable plastic tray; a sponge; a bath of water to dunk the workpiece in when etching is finished; paper towels in case of any mess; bicarbonate of soda to neutralise the etchant before disposal; all on a trash bag to protect the work surface.
The design is printed on a laser printer, then transferred to the brass using a hot iron. The toner acts as a resist to block the etchant from affecting the covered areas. There are a number of variations on this toner transfer technique. I tried using transparency film, but I had much better results using glossy inkjet photo paper. After ironing the print onto the brass and rubbing it down firmly, you can soak the paper off and carefully rub it away in layers, eventually leaving just the toner stuck to the metal.
I did the etching using the "sponge method": you use only a small amount of etchant, and gently wipe it over the surface so that the metal is continually exposed to fresh etchant. It's much faster than simple immersion. I etched for 10 minutes. When the desired degree of etching is achieved, you rinse the piece in water to stop the reaction, and finally, clean off the resist with acetone.
The results are in the second photo. It took a few attempts to get the technique down, you can see a couple of the failures at the top and the successful ones below. After a bit of drilling, cutting, filing and sanding they end up as shown in picture 3. I made 2 just as insurance in case I messed it up.
The final step was to antique the brass using a combination of brine and fuming with ammonia, as described below, with the result shown in picture 4. I also treated the brass hinges to match.
By the way the design of the escutcheon is a clue to the contents of the case Quick method for darkening brass by ammonia fuming:
First prepare the brine: 2 tablespoons of salt in a cup of water.
And set up the fuming chamber. I used a tupperware-type box. Put some household ammonia in an open container inside the box.
Use soap or solvent to degrease the brass hardware. If it's lacquered, you need to remove that first.
Dip the brass in the salt water, then put it in the box (but not in the ammonia!) and seal it up.
It'll darken very quickly. After a few minutes, open the box, give it another bath in the brine, and return to the fuming chamber. After about 5 iterations of this process, it should be a solid, consistent black.
Then you can use wire wool to rub the patina back to get the desired degree of shininess.