I'm working on a monograph / presentation on handling chemicals
(especially acids) safely in the jewelry shop. One of the questions
that I was asked to investigate is whether there are safer
alternatives to aqua regia for etching gold. So far, my research has
turned up a couple possibilities, which I'll mention briefly below --
anyone on the group have knowledge of these approaches, how well they
work, or any others not mentioned here?

Nitric acid elimination: as a substitute for HN03, use sodium
nitrate; disolved in concentrated hydrocloric acid, a (somewhat weak?)
solution of aqua regia is created. (This is the process Shor sells in
one of their refining packages). You still have all the hazards of
handling aqua regia once the solution is made, but at least you don't
have concentrated nitric acid around all the time, with its own
storage and handling issues.

Iodine/Potassium Iodide solution (usually in methyl alcohol,
occasionally other organic solvent): apparently this is used
routinely in the semiconductor/chip industry to etch gold. Etch rate
compares with that of aqua regia. Elemental iodine, of course, has
its own toxicity and handling issues. A commercial version of this
solution is sold as "Transene gold etch" to the chip industry.

Rauchfuss's reagent: this one is a relatively recent discovery, a
solution of elemental sulfur in N-methylimidazole. Disolves/etches a
great many metals, while (reportedly) relatively harmless otherwise.
Not much info available about it, other than the original research
papers and a few web posts.

Use of diluted acids to prepare aqua regia: how dilute can aqua regia
be, and still be effective as a gold etch? Do you have to use
concentrated acids? Would dilute acids, still in the proper chemical
proportions, be equally effective, and how dilute can you go? It's
been surprisingly hard to find any definitive answers to this
question, and what I have found is inconclusive.

Electro-etching: salt or other ionic solutions used in an
reverse-plating setup are commonly used to etch steel and other
metals, both ferrous and non-ferrous. I've seen a couple references
that at least imply that the process works with gold. Does it?

Cyanide solutions, of course, etch gold readily, but it's not clear
that's any better/safer than aqua regia in the first place...:-)

Some chemical references have suggested that almost any strong
oxidizer combined with a complexing/binding agent should disolve gold.
That's how cyanides and aqua regia work, for example. Not sure about
the I/KI solution, or Rauchfuss's reagent (I read his paper, but
didn't understand a lot of the chemistry, unfortunately).

Any help you can provide will be well appreciated.

(And for those who might refer me to Charles Lewton-Brain's book on
workshop safety, thanks, I'm already familiar with it; it's a great
book and will be acknowledged and liberally quoted in my writeup.
However, it doesn't answer this specific question.)

FYI, just in case you were wondering, waaay back when in college, I
was a chemistry student for a few years, which is how I got roped into
doing this -- I volunteered to someone that I knew a bit about lab
technique and handling acids....next thing I know: "Well, how about
working up some info for me...".

Best regards,

Bob Edwards
Chromis Designs
San Francisco