Step 4: Etching the Brass
I mixed 1/2" cup of Root Kill with 16oz of water to make the etching solution. I only needed 16 oz with the plastic tub I was using. You might need to make more depending on your container.
Root kill solution is not something you want to drink but getting it on your hands is not that big an issue, unlike the Ferric Chloride acid used in PCB etching. It's designed as a product to go down drains, so when you are done dump it in the sink and run water after it.
Take your brass strip of 2" tall and 10"+ long and bend it around in a circle with the can of spray primer. It's not going to be perfect, just close to a circlish kind of shape is OK.
You need some way of applying the positive wire from the power source into the brass dice piece. I stripped a little bit off the top of the brass piece end where there is no paint. Using a scrap piece of 3/4" wood, I used popsicle sticks and a spade crimp connector to make something that would provide power to the brass dice when it's in the etching solution.
Put the dice piece into the tub and fill with etching solution until it's higher than the longest word (in this case, "three") and lower than the scraped off part on the end. The brass strip circle will displace some but not that much. Put that in and check the level again - I would put in and take out a plastic spoonful of etching solution at a time to get the height correct.
From the power supply, the ground goes to the brass strip circle surrounding the brass dice piece. The positive connection went into an automobile lamp to control the current. Testing showed the lamp burned at 955mA or so, so that's what the power would be at. Putting the auto lamp in series with the etching tank, run a wire from the auto lamp to the brass dice piece. When power is applied, brass moves though the etching solution from the positive (brass dice piece) to the negative (brass strip circle). This digs out the exposed bits (the words of numbers) and leaves the parts covered in paint alone.
How deep and how quick the dice gets etched depends on the current and voltage being supplied, how close the brass strip circle is to the brass dice piece, how much copper sulfate is dissolved into the etching solution, if it's before or after the 2nd Tuesday of the month and who won the last World Series. In other words, everyone's situation will be different.
I let it run about a half hour, turned off the power and pulled it out. It was covered in brown gunk that washes off easily but the etching wasn't so deep. I let it run another 30 minutes and checked again. A little more etching but not deep enough. In the end I determined that in my setup, it needed to run 2 hours to get the etching level I wanted.
If you are running it with a current limiter, check it every 20 to 30 minutes. If you are running it full bore, you might want to check it every 10.
The brown gunk that collects on the parts being etched washes off easily in water. Keep a spare tub with water nearby you can dump it in when you pull it out of the etching tub.
When you get an etched depth you like, pull it out and wash it off. Now it's time to scrub off all the paint.