Thursday, April 30, 2009


Now that the toner is on the copper, we can etch it.
This means that you have to have made the tank, and found a suitable power supply.

The power supply needs to be at least three volts, and absolutely has to be DC, or direct current. According to my friend, who is doing second year engineering at the ANU, you need three volts for the copper to start coming off the plate. Much more than three volts is overkill, but it does no harm. However, the higher the voltage, the more leeway you have (theoretically) with the size of the plates and the distance between them, as well as the concentration of the electrolyte solution. If you measure the voltage across the two plates while they are etching, it reads higher the further apart they are. This is because of Ohm's law, which states that Voltage=CurrentXResistance, or V=IR. If you move the plates close to each other, the resistance between them drops, causing the voltage to go up. The same goes if you put more copper sulphate into solution.

The procedure for etching is this: Figure out some way of suspending the plate as close to parallel as possible with the cathode. I drilled two holes, one near each of the top two corners. Then I put some fencing tie-wire through the holes and hung it from a bit of aluminium stock so that it would hang below the water line.

Connect the positive of the power supply to your piece, and the negative to the plate in the tank, and turn the juice on.

Every fifteen minutes or so, turn the power off and scrape the crap that forms on your piece off with a toothbrush. Return it to the tank and continue.

This particular piece only took about half an hour to etch, but that's because it's so small. The bigger it is, the longer it takes. This is because the current will spread out pretty evenly over the surface of the copper. Because there is only so much current, if you have a large plate, there will be fewer amps per square centimetre. I once etched a card box with a picture about 5X7 cm, which took about two hours.

Here's the badge that I etched, based on the picture in the second post. The lines were about 0.5mm deep, and very clean. The only problems with the etching quality are the parts where I failed to transfer the toner properly, i.e the wing tips, and three parts of the zeppelin. The other flaw is that there is some pitting on the wings, but I suspect that that is due to the large spaces of black. It might work better if that part of the picture were made up of lines.

If that is where you're going to leave it, then now is the time to ink it. This can be tricky if you don't have the right stuff, but it's not all that bad. If you're going to do something else, you shouldn't ink it yet.

Interesting fact: I touched the back of the plate before etching, and was left with an etched fingerprint on the back. The back does etch, but not deeply.

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