Here's how I etch my blades:
Firstly, these are some nasty chemicals so proceed with caution, good ventilation is always a must and keep your chemicals in tightly stoppered containers, well labelled and out of general reach. Ferric Chloride will lose effectiveness if exposed to light over time, I keep mine in a brown chemist bottle. Caustic soda I mix up as needed.
Last night I sprayed the blade with Positiv20. It's a photo-reactive spray-paint and dries dark green. Sorry about the photo - taken in a dark room with minimal light - photo-reactive remember
I then take one of my negatives and put a thin strip of tape along one edge:
I stick it in position, the tape helps hold it in place while I clamp it down with sharpened clothes pegs:
Once I'm happy with the placement I expose it to direct sunlight for 15-20 seconds. Make sure there are no shadows on the logo area and keep your hands still. 15-20 seconds is plenty, too much more and you'll "burn" the Positiv20.
After exposing it to sunlight the exposed paint turns dark blue and can be washed away with a weak caustic soda solution. I pour a couple drops onto the blade and after a couple seconds tha logo starts darkening and popping out of the paint. I then flush the blade in fast running water to remove the softened paint. Here's the result:
The logo should be sharp and shiny with no paint left inside of it. If you're unsure, re-apply caustic soda for a couple more seconds. I draw a"moat" around the logo with sharpie, it'll stop the acid running out of the area you want it in
I then put a couple drops of ferric chloride onto the area I want to etch. It's pretty viscous (as in the "thickness" of the liquid) so it forms a pretty stable droplet. You only need to cover the area to be etched but overlap the logo just a bit.
I count to 200 then flush the blade and check the etch. It'll etch better in warmer weather, I do a couple etches in winter. If necessary, re-etch NOW - once you remove the Positiv20 it'd be damn near impossible to get the logo back in the same position, so be sure before you move on.
Once you're happy the logo is nicely etched you can wipe the blade down with acetone to remove the Positiv20 - always a nerve-wracking time - I hate botched etches.
This one came out a beaut though - deep and dark - very chuffed:
