Photo-Etching

[piersyf]

OK, like I said the process I use is NOT photo etching. I understand that there is a process that can be done using my preferred chemicals but it needs a laser printer and a special transfer film. I can't afford them.

I researched etching as a part of my first degree and spent 6 months in a closed chamber with very powerful extractors and buckets of reagent grade acids. Good fun, but not something to do at home. I checked around the electrical stores for the materials they use for making printed circuit boards and found the 2 most common etchants were ammonium persulphate and ferric chloride. I went with the AP for 2 reasons; it comes in a crystal form that you mix with hot water (meaning the strength of cut is infinitely controllable) and the material is also a lot cheaper. As to disposal all you need to do is flush with lots of water to bring the Ph closer to neutral then just tip it down a drain (this may differ in your region...). There are fumes, but you aren't at risk unless you actually sniff them. They will burn your nose and lungs. Anyway, on to the process!

Take said sheet of copper alloy (copper, brass, bronze) and polish with fine grade wet and dry paper. It should be coarse enough to take a pencil line. Then draw/trace/whatever the thing you want etched. Of course, you are indicating the areas that are not to be cut. Be advised also that pencil lead has just enough wax to occasional act as a resist.

The primary resist I use is a derivative of asphaltum which is used as a resist by jewellers. I get mine from the hardware store: the black stuff used to seal the wounds on trees after they've been lopped. It is a runny tar compound. It can be thinned further with turpentine. Get it to the consistency of enamel paint, then load up your ruling pen/paint brush and away you go.

For those who don't know, a ruling pen is something you get with decent compass sets. It's the thing with a straight and bowed metal part with the gap adjusted with a threaded screw. The gap is to set the width of line you want. They take some getting used to, but will rule lines with absolute accuracy when you get the hang.

Other resists are enamel paint, resist pens, wax, basically anything that will stand up to water that is just short of boiling for about 10 minutes.

The mixing instructions for the crystals is on the bottle, but basically you add about a tablespoon to a dixie cup of water that boiled a few minutes ago (about 85 degrees C). Dissolve the crystals with a spoon (plastic or stainless steel... the etch won't touch stainless. It WILL etch mild steel). Shove said painted and dry article into the etch for about 10 minutes, then retrieve, run under water to stop the etch process, then wash with turpentine to remove the resist (it dissolves easily).

That's enough to start, and to get the idea. The crystals cost about $10 or so for enough to do about 30 or 40 etch baths, so plenty of playtime!

And Will, yeah, what I thought too... separate layers sandwiched according to the design for double and triple structures... very sweet! A ways off though I'm afraid. I'm in the process of scratch building a Humber 4x4 heavy utility and it's taking a long time.

I will say that this thread got me thinking of another project on my 'dream' list; a plastic and etched brass LCT4 that can have a mold made and cast in pewter.