Etching metal is one of my favorite metalsmithing techniques- it's a great way to create a surface pattern or image in metal.
If you want to give etching a try, I would recommend starting with copper. Copper is easy to work with and inexpensive, and copper etching solution is relatively safe to work with and also inexpensive.
The basic principle of etching any metal is to apply a substance to the surface of the metal which will resist the bite of the etching solution. This substance is called resist. Once the resist is applied, all you have to do is submerge the piece in the etching solution and wait for it to etch.
Here are the materials you will need:
-18 or 20 gauge copper
-Scotch brite or steel wool
-Resist- possible options include paint markers, nail polish, asphaltum varnish, press and peel film... For this tutorial I will show you the one I like to use- It's called stop-out varnish and it's basically a red tinted shellac. I got it from Dick Blick. Commenter Wolfgang pointed out that acrylic paint also works as a resist. (Thanks Wolfgang!)
-Something to apply your resist with. I will show you how to apply resist with a nib pen but you can also use brushes.
-Solvent- my stop-out varnish resist dissolves in rubbing alcohol. For other resists you will need acetone or mineral spirits.
-Etching Solution- Ferric Chloride (also called PC board solution) you can get it from electronic supply companies, or from printmaking supply companies. I got mine from Dick Blick
-A plastic tub
Before we get started, I would like to take a minute to talk about safety issues. Ferric chloride etching solution is really quite safe to use. It is actually not an acid, but a salt. It only etches copper and brass. It can irritate your skin though, so wear rubber gloves. Also, ferric chloride is very staining. It will not come out of floors, clothes, etc and will take days to come off your skin so be careful!
Now here's the step by step:
1. Prepare your metal.
Resist sticks better on clean metal with a slightly rough surface, so give your copper a good rubbing with scotch brite or steel wool.
2. Protect the back of the metal.
I like to be extra careful so I start by painting a thin layer of resist over the back of the copper, then when it dries I cover it with masking tape. Use an old brush to spread the resist, and clean it with rubbing alcohol when you are done.
3. Apply the design.
I use a metal nib pen to draw the resist onto the copper. I just fill a little cup with the resist, dip my pen in and draw it on. It's a little thicker than ink, so it takes a little getting used to. As you are drawing the design, the resist will start to dry and gum up the pen. I keep a little cup of rubbing alcohol handy, and when the resist starts to dry on the pen, I dip it in the alcohol and wipe it clean on an old rag.
I've used a sharpie to mark out the borders of my designs. Sharpie is sort of a weak resist itself, so it may leave a faint mark on your etched metal. I'm cutting the pieces out where the sharpie lines are anyway so I'm not worried about it.
This resist dries really fast, so just let it dry for 15 minutes or so and it is ready to go in the etching bath.
4. Etch the metal.
Pour your etching solution into the plastic tub. I like to use a big plastic container with a lid, because I can just put on the lid to store the solution.
When using ferric chloride, the copper needs to be suspended design side down in the etching bath. To do this, I just put a long strip of tape across the back of the piece, then place it in the etching bath just below the surface, with the ends of the tape attached to either side of the tub.
Depending on how deep an etch you want and how fresh your solution is, etching can take half an hour to three or four hours. Just be sure to check the piece every so often. Just pick up one end of the tape and lift the piece out of the bath. It helps to give the surface of the copper a little rinse with water once in a while too.
5. Remove the resist.
Once you have a deep enough etch on your copper, remove it from the etching bath, take it to the sink and rinse it off. Take a cotton ball and saturate it with rubbing alcohol and rub off the resist. Once the resist is off, it's a good idea to scrub the copper with some soap and scotch brite. Sometimes the residue of the etching solution will continue to etch the metal even after you remove it from the etching bath. To prevent this, you can scrub the metal with ammonia to neutralize the etching solution. (Thank again, Wolfgang) If you have a torch, I would recommend annealing and pickling the copper just to make sure it's completely clean.
You now have an etched piece of copper that is ready to be cut, formed, and finished in any way you like.