So you have the design correctly transfered? Congratulations! You just have it after about a dozen tries, but that's ok since the following process is way more accurate:

ETCHING WITH SALT WATER

The first thing you need to do is to prepare a salty water solution in a PLASTIC container --never use a metalic container!-- You can use a soft drink bottle cut in half, a bucket, whatever. Toss say a bunch of table salt, like 1 spoonful per half a litre. I don't have an exact measure, for me anything worked. Then stir well until you don't see salt in the bottom of the container. Add more salt if you want but it shouldn't get into the bottom, which means you are wasting it. Then the nice trick:

With scotch tape, spray paint, electric tape, wax, crayon, permanent marker, etc, cover all the area you dont want to etch, and that includes the backside of the piece. ANY area with naked metal WILL be etched. Take your time, cover the thing well.

Now, put the metal rod into the water, vertically and attach the - negative of your power supply to it. Attach the + positive wire to the piece with the design. You can use alligators but don't let them in contact with the salt water because they WILL get etched too!

With all attached, turn on the power supply. You will see bubbles around the metal rod, if you don't then the power is not well connected. After seeing bubbles, go and get some coffee, beer, etc and wait for the piece to get etched. The water will turn green, then black, then brown and it will start to form a kind of toilet matter on top...looks very very nasty but it is not poop so it won't smell anything, it is just floating steel rust.

Occassionally stir the gloppy solution and also check the etching, just take the piece out and clean it slowly and gentlely with a cotton cob. If you want more depth then toss it again into the etching glop. If the solution gets too nasty, you can prepare more and keep etching.

I would say it can eat 1mm down in a flat 3" square piece in about 1h. But it depends I guess on the metal material.

Once you are satisfied with the etching, remove the piece from the etching glop, wash it with running water, toss the etching solution --I think not in the drain, I don't know if it will eat the drain metal pipes--, wash all the "equipment" and get into the finishing process you want for your piece, say polish with wool steel, galvanize it, paint it, etc.

And that's it. The most unbearable step is to transfer the design correctly for me it never works at first, unless it is a fat steel piece like a tsuba.

NOTES
* Flip your design before printing if you have letters or stuff that needs to be correctly orientated in the piece.
* The thinnest line width I have had good results, ie won't be lost in the etching process, is 0.75 point.
* For copper sand the piece with 200~300 grits...mirror finish in copper is not good and won't accept any transfer
* The salt water etching "glop" is not toxic to the skin, it won't do you anything but it will stain a lot
* The gas from salt water etching is toxic if it was massively expended, for what I do I can even do it indoors but my wife will kill me becasue the possible stains --it really looks bad ladies and gentlemen
* Never bake the paper when heating the piece, it will bake the toner
* When heating the piece you don't need to super heat it, if it is fat it will remind hot for a while
* Carefully heating thin pieces they will get too hot too fast, and in the case of copper sheet it will actually soften the copper!

And that's it. If you want more explanations let me know!