You can see it in action here:
Please, don't send any Bitcoins to the address on the wallet. If you must send them somewhere, how about here: 13AEtsPjyDm8SdhQFcwUMDJZYgR5hteZPS :)
Its possible to etch stainless without anything particularly exotic. (I used a bench-top power supply, but thats about it for even remotely out-of-the-ordinary.)
We will use the laser-printer toner-transefer method to make a mask, then apply it to our target steel, and then etch!
A Note About Safety
This etching process is safer than many others since there are no acids involved. However, there are still some things to consider.
First, the process will split the water into hydrogen and oxygen gases. Hydrogen is flammable and when mixed with oxygen, down right explosive. You don't want to let those gases accumulate. Use plenty of ventilation to prevent the gases from concentrating.
Second, stainless steel is made stainless by adding Chromium to the steel. After etching, there will be contamination in the water from the steel. The only part you have to worry about breathing and environmentally is the hexavalent chrome or (Cr VI). Avoid breathing the fumes from the etching and treat the waste water an an environmental hazard. (It is probable that the concentrations from this project will be too low to officially be considered a hazard, but rather than have it tested, lets just treat it as such.)
Feel free to reuse the solution as much as you can, but when it is time to dispose of the solution you should let it evaporate and then dispose of the remaining solids by tossing them in with some other stainless scrap. Find a local machine shop that works with stainless and toss it in with their stainless scrap.
Step 1: Preparation
You'll need a plate of stainless steel. About 3x6 inches.
You'll need a DC power supply of some sort. I used a fairly large bench-top version, but you can use just about anything. It just might take longer to etch. Anywhere from a 9 volt battery (maybe) to a wall-wort, to a hacked ATX.
Steal yourself a few pages from a magazine.
I've hacked together a script to create the wallet and the mask image. It was built and tested on my Mac, but it might work on Linux as well. https://github.com/brendanjerwin/cold_steel_storage
Take a look at the README for details on the script.
Sand and clean your steel well. Often there is a finish that must be removed. I used a sander, then a steel kitchen scrubber, then Bar Keeper's Friend. Then dry it off and set aside.
Step 2: Print and Apply Mask
We are going to print the mask with the best print quality on a page torn out of a magazine.
Magazine paper is pretty good for this since it is high-gloss (the gloss is clay, not plastic) and nice and thin, so the heat moves through easily _and_ it removes easily after the mask is transferred.
Open the mask PNG created with my script in Preview and print it. It will try and scale the image to fill the page, but don't let it. Also, be sure to choose the best print quality, and if you can, let the printer know it will be dealing with some flimsy paper.
Once you have a good print, trim the mask on the long sides, leaving tabs on the other edges.
Oh, while this is going on, you should go ahead and preheat an iron and lay it on the stainless sheet...
After the stainless is preheated, move the iron and carefully but confidently apply the mask.
The steel is hot, so as soon as the toner touches it, it will stick. Get it lined up pretty well on the first try or you'll have to scrap it, clean off the steel, and try again.
After the mask is placed, you have to fuse the toner to the steel. Move the iron around, being sure to apply moderate pressure across the whole mask.
If you don't heat an area, the toner wont transfer. If you heat an area too much, with too much pressure, the toner will smudge. (Thats what happened with the public address portion of my prototype.)
Once you got it transferred, turn off the iron and carefully transport the steel to the kitchen sink!
Step 3: Reveal the Mask!
Don't be afraid to let it sit for a while, the softer the paper the easier it is to remove.
Pick at and gently rub the paper until it is all removed.
Once you've gotten all the paper off, you can inspect the mask to see if it looks like it'll work.
Step 4: Test QR Codes
Take a picture of the codes on the mask and load it into a image manipulation application of some sort.
Invert the colors and point your phone at the screen to see if the QR is readable.
If they are not readable, double check that you've inverted the colors and if they still are not, clean the steel plate and start over...
Step 5: Etch!
Fill a bucket with enough water to got at least an inch or so above your piece, standing long ways.
Get a piece of scrap steel and attach it to the negative of your power supply.
Dump in a bunch of salt and stir!
Prepare the Piece
Attach a wire to the back of the piece and tape over any parts you don't want etched. Connect the wire to the positive terminal and submerge the piece on the opposite side from the negative terminal. Face the mask towards the scrap on the other side of the bucket.
Turn on the power and watch the bubbles form! NOTE: The bubbles are water being split into its constituent Oxygen and Hydrogen atoms. Both gases. And, when mixed, a rather potent explosive. You probably don't want to let the exhaust concentrate anywhere. I left the door to the backyard open.
How long should you leave it in there? Well, I wanted a deep, long-lasting etch so I watched two episodes of Futurama while it was etching. That seemed to work pretty well with my setup. Just keep an eye on it, turn off the power every once in a while and take a look at it.
Step 6: Done Etching? Clean and Enhance.
Once you are satisfied with the etch depth, you have to clean the mask off the steel.
I used Acetone some, but actually had better luck back in the kitchen with the scrubber. The etched steel isnt fragile, so you can go to town on it!
The contrast of the etching isn't great for scanning the codes. I was able to get it to scan with some careful control of the light, but who needs that?
In order to improve the contrast, I filled the etching with black wax.
I heated the piece on the stove a bit and then just rubbed a crayon on it.
I scrapped off the excess and polished it a bit with a paper towel.