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Safe acid etching of aluminum
Q. I have been asked to take an 1/8" piece of aluminum and etch away much of it for an art piece. My last and only experience with acid etching was in a school environment more than a decade ago. I recall vapors and the novel approach of pouring the excess down a storm drain. Needless to say I need some help. Either I can do the line art and a professional company can etch it for me, (referral appreciated), or I need to find out how to do this in a manner that is affordable, safe and not destructive to the environment. Any Idea?
studio - Santa Monica, California
A. You should probably use sodium hydroxide, not acid, to etch aluminum. This material is also known as caustic soda, and the chemical formula is NaOH. The most accessible form is probably Drano [linked by editor to product info at Amazon]. I don't believe there is any necessity for significant environmental impact (but there ARE safety issues).
As for the environmental element, after the NaOH has dissolved the aluminum, you can neutralize it with vinegar so that it is neither acid nor alkali. The precipitate will be basically aluminum hydroxide, which is a major component of the earth's crust and non toxic. Aluminum salts are used in water treatment and wastewater treatment, so I see no problem in flushing it as long as you are talking a small quantity from an artist, not an industrial quantity. The aluminum may be impure, and release some copper or other metals in the precipitate, but again I think this will be very minor--in the same range as from scrubbing a copper bottomed pot. But considering your neighbors who clean their pipes with Drano, it seems like nothing to worry about environmentally.
But the safety issues are another matter. Sodium hydroxide can blind you from a single drop in the eye. And the heat of dissolution or neutralization can cause water to flash to steam and make the solution erupt all over you. Plus, sodium hydroxide will kill a person if they accidentally drink it. If a person has lab or chemical training, and personal protective gear on hand, I think they could handle it. In other words, this is a chemical and a process that CAN be handled without incident, but only if you know exactly what you are doing and handle it with a rational fear of the possible consequences of lack of care or accident.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
A. Search for etching, photoetching or gravure in your favorite search engine. If yours is a one time only operation the following generic answer might do: paint your artwork on the aluminum with acid resistant commercial enamel and immerse in a solution of caustic soda 30%. Little amount of dissolved aluminum residues and the soda will not harm the environment or the drainage pipes noticeably. For large operations find local expert assistance.
Monterrey, NL, Mexico
Q. I am in industry and want etching on aluminium by Acid. Etching on aluminium by NaOH disturbs the masked portion. So, I want any acid.Raj Tuteja
watch hands - New Delhi, India
January 23, 2012
A. Google up copper sulfate mordant.
It's a mixture of copper sulfate, table salt, and the active ingredient in Sani Flush.
It supposedly won't burn you if you get some on your skin, and all the ingredients are routinely poured down the drain so eventual disposal is easy (although it can be reused).
If you also Google up home-built circuit boards, you'll find many people are laser printing onto paper, then ironing the toner onto an item to be engraved, and dissolving the paper off with water. The toner acts as a mask for etching and is then washed off with acetone aftewards.
Some very intricate designs can be etched this way using simple graphic programs as the design source.
- Fargo ND U.S.