Allrighty then.
- in PCB making and fine pattern-transfer etching (I've done lots of that), they use UV-sensitive resist.
You brush or spray it onto the clean surface (be it a pcb or a blade), let it dry (hairdryer/oven helps).
Pattern (positive works the best) is printed onto transparency.
To make sure blacks are black, I double print on a common laser printer. Making sure passes align, is a b1tch, takes a couple of tries.
You lay tranparency atop of metal, secure it so it doesn't move (scotch tape)
and blast it with UV light, using $4 workshop light fixture from Lows and $9 keep-your-pet-reptile-warm UV lightbulb from a pet-supply store. 20 mins seems to work the best, lamp being 20" or so from the surface
Exposed resist is polymerized (hardened) by UV light. Whatever is protected by the print, stays soft. Now, the thing is bathed in solvent (caustic soda is used sometimes) and it washes away soft resist. Timing is critical, as it will start eating into hardened resist as well, if you let it sit in solvent for too long.
More drying with hair dryer. Now, you have to mask the other side of the blade and whatever other areas that you want to protect (tang etc). common shellac spray/can works fine. Do a few layers. Use a fine 10 cent brush to do fine masking out.
Into ferric chloride it goes, 30 min or so. You need to watch the etch carefully and get the knife out in time. Etchant will always find some microscopic holes and will etch there too if one is not careful. Resist
will lift too, if left in etchant for too long.
Asphaltum is probably the best resist, being very dense and easy to see
(it is pitch black). You buy asphaltum powder (printing supply stores carry it,
it is dirt cheap, _VERY_ fine powder, be careful with it, don't want a pound of it go airborn and settle throughout one's house) and mix it with some beeswax and strearine. I don' t remember the proportions. Do it over a stove
of some sort, outside. Don't let the wax smoke, as it will ignite past that point and wax smoke is bad for you. Pour the mix into some form. I made sticks out of mine - milled some 3/4 x 3 x 3/4 channels in a piece of wood, lined it with kitchen foil and you're done.
To apply, you can heat up the blade where it melts the sticks. Or, melt some resist (dont let it smoke) and apply with a brush.
You can scratch designs into asphaltum resist - that's how some of Boye's
knifes were etched. Need to be fairly artistic for that. Boye used Aqua Regia, a real strong and real nasty mix of nitric and sulphuric acids . Ferric chloride is 1000 times safer, won't burn you skin (it _will color it yellow). Still if you store it in a shop, close the lid tight, as wapors are highly corrosive.
FeCl is best when bought as dry powder. Quite a few places carry it like that. There's no hazmat charges when shipped as powder. Mix it it distilled water, outside, slowly (the water will get hot). Wear a better breathing mask, as the powder is real fine and eating an apple is a much better way to get some Fe into your body. Of course, it needs to be mixed/stored in a plastic container, not metal.
