The Saline-Sulphate solution: The non- toxic nature of the saline-sulphate etch does away with fume cupboards or specialist ventilation, combined with the cheapness of materials and the diversity of available resists make the medium ideal, not only for established printers, but for schools, colleges and even the home studio.
Being an advocate of everything natural, I use this solution of copper sulphate crystals, table salt and water that will etch zinc and mild steel plates perfectly. I can buy the crystals locally, and luckily they are cheap and safe to transport as it comes in powder form. The process is simple, just mix the dry ingredients with warm water in the etching tray and the bath is ready for use.
The Saline-sulphate etch is a transparent blue-green hue when fresh, and the only gas it produces is hydrogen. On the down side, I have heard disparaging remarks because it becomes dark green and fairly opaque when used and gets pretty messy, but I consider this is a small price to pay for safer etching.
There are also a ranges of oil based/water soluble inks that can be cleaned off with vegetable oil or soap and water.