Friday, 9 August 2013

Electrolytic Etching Steel

Some time ago, I wrote a puff piece about a reproduction 15th century crossbow that I made. One of the things that I mentioned in passing in that  article, was that I electro-etched the metal on the piece to add design and “age” to the finished product.

It’s probably worth exploring the process, since it certainly isn’t hard, but it is a worthwhile technique to know.

Basically, electrolytic etching is a process where you immerse a positively charged piece into a negatively charged solution. The positively charged ions in the metal (anode) are attracted to the negatively charged point (cathode) through a process of oxidisation. Or … put simply, the solution makes the metal rust, the electricity takes the rust away from the metal.

The art in electrolytic etching is in the design and execution of the resist.

To make the crossbow parts, I painted the steel pieces with a black acrylic paint and allowed it to completely dry. Then I drew the design onto the painted piece and scratched the design using an awl. You could just as easily use a nail, pin, fingernail … whatever will remove the paint, exposing the bare metal underneath. I also attached a copper wire to the back of the steel piece to connect to the anode (connected to the positive source).

I made up a saturated saline solution mixing the salt in until the water is saturated (that is, no more salt will mix into the solution).

The piece was then immersed into the solution connected to the positive rail of my power source (a 12V battery charger). The cathode was then immersed into the solution (via another copper wire) and the charger was turned on.

You should see bubbles rising from the exposed metal on the piece … this is from the oxidisation process. Tiny flakes of steel will be coming away from the piece also and going into the solution.

I gave the pieces about 15 minutes in the solution before taking them out.

Next, I used some steel wool and running water to scrub the paint away from the pieces and gave them a good polish.




These “freehand” etchings are quite nice and are satisfactorily “distressed”. There is some pitting that has occurred in the design, but these are entirely suitable for the end result that I was looking for.

An alternative method for producing the design, that I have used successfully with printed circuit boards and which works just as well with electrolytic engraving, is to print the design on a laser printer (onto a gloss or semi-gloss paper) and transfer the design onto the metal using the iron-on transfer method (remember to reverse the design).

To iron the design onto the metal, turn your household iron up to it’s hottest setting, place the paper onto the metal piece (ink side down) and iron it on. This will take up to 4 minutes of pressing and moving your iron around onto the piece. Drop the metal piece into hot water and let it soak for about 15 minutes. Carefully peel the paper off until you are left with just the metal and the toner.

Use acrylic paint to coat the back of the piece and to touch up any bits that are not in the design. Attach your anode and proceed as described earlier.

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