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[Randall]

Yes, it's the same process as PCB etching, using 1 part hydrochloric acid and 2 parts 9% hydrogen peroxide.

How do you dispose of the used etchant? And do you print a mirror image first?

[Tom Phillips]

Yes, it's the same process as PCB etching, using 1 part hydrochloric acid and 2 parts 9% hydrogen peroxide...

Mick. What is the strength of the HCl that you use. Is it the strength commonly sold as swimming pool acid?
Regards,
Tom

[Mick Bailey]

It's labelled 'maximum concentration 37% HCL' which only states the maximum concentration that it could be. Probably 30% - 35% Usually acid referred to as 'commercial grade' is within this range. Pool strength acid is usually around 30% and this is perfectly good.

The concentration I use fumes when opened. You need plain acid - some branded products also contain detergent, colouring and phosphoric acid.

You may also find it as brick, tile, quarry tile or cement cleaner. I've seen it in farm shops here in the uk, but there's a pool chemical specialist that I buy a whole range of chemicals from - they seem to be able to get most legal chemicals - including straight hydrochloric acid.

[Steve Conner]

Here's a picture thread: Etched enclosures

Thanks Mike! Those look great, so many ideas for my next build! Even the "bottom of the lake" look from an etch gone horribly wrong would suit some pedals.

[Mick Bailey]

Used etchant is a problem for disposal. You can't put it down drains because of the copper content. It readily kills micro-organisms and lower forms of plant life, such as mosses and algae, including the bacteria that break up waste down at the sewage works. Also, I'm not on mains drainage so have to be careful what I put down the sink or flush down the toilet.

My local waste site will take hazardous substances in small quantities for free. I evaporate down what I can during the summer months to reduce the bulk. I've also used it dilute to kill of algae on my house. I've also tried precipitating the copper out and neutralising the acid, bot it foams too much to be practical.

I've found the best way is to mimimise the amount used in the first place. I etch in the smallest possible container with a depth of about 2mm above the surface of the blank. Agitation is the main thing. When you rock the dish don't worry if the metal gets exposed. Incidentally, halfway through I turn the dish, otherwise one side will etch deeper due to the 'handedness' of the rocking motion.

I do my etching in a batches to exhaust the solution and get the most out of it.

It is mirrored - it has to read right way round when applied, for badges etc. What you see is what you get.

[J M Fahey]

FWIW copper added to aluminum makes it *much* more affected by corrosion.

In fact, at the beginning of the last Century copper/aluminum alloys looked like a solution for long distance power transmission ... and failed miserably when exposed to the elements.

Only solution was to go back to pure aluminum or make "alclad" composites; alloy core with external pure aluminum surface.

So, I *think* that may be one reason why cast aluminum boxes are more easily corroded than , say, sheet aluminum.

Zn should also increase corrosion while Si should be reasonably neutral.

I have aluminum sheets custom made for me at a recycling factory.
Great price and very good mechanical properties, plus the big factor that I order them in scrapless sizes so I have no waste at all, but have to mechanically treat the surface (blasting/wire_brushing/sanding) before chemically treating it prior to painting, or I can easily see large ugly "stains" showing surface is not chemically uniform.

While if I buy (much more expensive) original ALCOA or KAISER pure electrolytic aluminum sheets the surface is perfect.

Since I always use painted panels, the choice is obvious

[Mick Bailey]

The flip side of this is that aluminium added to copper is more corrosion resistant once small amounts of additional alloying elements are added such as nickel - hence the use of aluminium bronzes for marine applications.

I get my aluminum sheets from a stockholder that has random size offcuts and damaged sheets. Sometimes there's a scratch on one side or the corner is bent. I get some waste, but the cost per chassis is very low.