Monday, May 4, 2009

Metal Etching

While I may not have been posting much lately, I haven't been (completely) idle. I did slow down there for about a week or two, due to being ill, but I'm back on track now and I have a few new projects under way.

Ever since I found Jake Von Slatt's article on DIY galvanic metal etching, I have been fascinated with the results. But, much like using photo-emulsion for screen printing, I hesitated to try it because it looked difficult. Finally, I got up the courage to give it a try. This is very much an experiment in progress, so I don't have a lot to report just yet. At least nothing terribly exciting, but I will post updates as the experiment progresses.

It took me several days and several trips to multiple stores to find the copper sulfate. Neither Wal-Mart, not Lowes or Home Depot (at least not my local ones) carry the Root Kill mentioned in Von Slatt's article. Finally, I found another brand, called Root Gone at a new Menards that opened in Massillon recently. Shortly after, I read Von Slatt's follow up article which told me that I could have gotten away with using salt water instead. Live and learn. Well, now that I have the stuff, I plan to give it a go anyway.

I started off by experimenting with the photo copy transfer technique mentioned in his article, but I had very little success. Of course I wasn't following the instructions exactly, because I didn't have the proper equipment (i.e. a laser printer). I tried using a plain paper photo copy, because I had one lying around, but it didn't work very well. When I get around to going out to Kinkos, I will try it again using the photo paper that was prescribed in the article. A new blogger, Mr. Able, has promised to post a tutorial on his etching method (which appears to work spectacularly) over on the Brass Goggles Forum. Maybe I'll just wait for that. I decided to ditch the photo transfer resist idea (for now), and just do something simple, like using tape or contact paper as a mask. That would at least allow me to experiment with the etching process a little. I could perfect the masking process later.

I mixed up my copper sulfate solution and brought in my 10amp car battery charger. I didn't use a battery for a buffer (though I probably should), because I didn't have one handy, and because I didn't think it would be necessary as long as I was careful. For both the cathode and anode, I used a piece of 36 gauge copper art foil approx. 3 inches square. Following (somewhat) the Galv-On method described on the Greenart web page, I placed the piece to be etched on the bottom of a disposable Gladware-type sandwich container, then laid a piece of felt on top of it to prevent contact with the anode. On top of that, I placed the anode plate, and filled the container with the copper sulfate solution to just cover the plates.

I switched on the juice, and watched. The amp meter on the charger was reading a steady 10 amps, which I thought was good. The breakers didn't pop, which I thought was even better. It didn't take long (a minute or two) to start noticing some action in the container. The anode and felt prevented me from seeing what was happening with the etching plate, but I could see some bubbles and some black waste product seemed to be forming in the solution. I stared getting nervous that the felt was melting (it was cheap synthetic craft felt, not wool), so I shut it down and removed the felt and examined the plates. There was some copper residue on the felt, but I didn't see much etching on the plate. I replaced the felt with some folded up paper towel (at least it won't melt, I thought) and returned the plates to the container for another go. I had no idea how long this process should take, so I left it in for about 15 minutes, then checked it. The results were disappointing. While I could see there was some galvanic action going on, I couldn't see much etching (at least not controlled etching). There was definitely something happening to the plates,but it was hard to tell exactly what. Only the edges of the plate looked like they showed significant thinning.

A second attempt was made using a different piece of copper foil for the etch plate, and a different material for the mask (masking tape). The results were largely the same.

On the third attempt, I used enamel model paint as the mask. Something happened on that third attempt that I can not explain. The rig was set up exactly the same as before, but this time the charger spiked up to 50 amps. The solution boiled rather quickly. I kept turning it on and off, and trying to adjust the plates, thinking that I was shorting something out, but it kept bouncing up to 50 amps. I wasn't doing anything different than I did on previous attempts. I could not explain it. Anyway, I kept it going for a short time (about 15 minutes) and then turned it off to check on the plates. The etching plate had been almost completely dissolved! Though on the small scrap that remained, there were a few spots that were raised, where the mask had been (the paint was now entirely gone), so that was somewhat encouraging. 50 amps for 15 minuted was clearly far too much. But my current rig would not allow me to see what was happening to the plates, nor did it give me much control over their spacing.

I knew I needed to make another rig, closer to the tank style that Von Slatt used. I set the etching aside for the moment and set about building a new rig. I cut several pieces of clear thin Plexiglass with the Dremel. Normally I use a rigid cut off wheel for this, but this time I opted to use a flexible sanding disk. I didn't think the sanding disk was quite thick enough to hold up to cutting, so I backed it up with a piece of card stock cut to the same diameter. I was actually surprised at how well this cut the plexi. Both the way the pieces were cut, and the way they were glued were both experimental (for me). I had recently purchased a special glue made specifically for gluing acrylic. I used a medical syringe as an applicator (my mother is diabetic) and it worked amazingly well. I ended up making a plexi tank about 2 inches wide by 4 inches long by 6 inches deep. Here you can see me leak testing it with some water. No leaks, on the first try!

Time to put the new tank rig into service. This time I switched to a brass foil (also 36 gauge), and used vinyl contact paper as the mask. I removed the car charger and replaced it with a single C cell alkaline battery. With only 1.5 volts and a tiny fraction of the amperage, I wasn't sure if the battery even had enough push to make any effect at all. To increase the conductivity of the solution, I added a little sea salt to the mix (though I'm sure it wasn't necessary). I figured it couldn't hurt. It was late, and I was tired, so I hooked it up to the battery and left it over night.

When I came back (14 hours later), the results were similar to experiment #3. Most of the metal that wasn't protected by the mask was completely eaten away. However, the mask did remain in place, and the metal under it was only minimally affected.

On the plus side, the low voltage allowed the released copper to properly attach to the anode plate. While the earlier experiments produced copper buildup on the anode, it washed right off. This time it was well and truly electroplated. Interestingly, something about the electroplating process caused thin parallel ridge lines to be formed in the copper plating. They were very uniform and ran vertically (from the top of the tank to the bottom of the tank) along the entire front surface (facing the cathode) of the anode plate. No such lines existed on the original foil plate. I have no explanation for the phenomenon.

Click on the pic for a close up of the lines.

  • 36 gague foil is a little too thin for this process.
  • 50 amps at 12 volts for 15 minutes is too much.
  • X amps (probably less than 1 amp) at 1.5 volts for 14 hours is too much.
  • Lower voltage allows for adhesion of the copper buildup on the anode.
  • More study needed.

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