Although my specific interest is electrolytic etching I've recently
discovered a fine online reference for etching in general. It is the
"Metallographic Etch's Database" at
http://www.kaker.com/etch/java/index.html.

In it there are a number of entries for gold including a couple _not_
using Aqua Regia:

Material: Palladium (Pd), gold (Au) and platinum (Pt)
Type:: Microetching
Method: Chemical etching
Etchant (electrolyte): 100 ml distilled water, 10 g ammonium
persulfate.
Procedu 30 s to 2 min.
Remarks: For Au alloys with high content of precious metals. White
gold. Pd and Pt alloys.
Reference: G.Petzow, Metallographic Etching, ASM (American Society for
Metals), 1978, p. 45.

Material: Gold (Au), palladium (Pd), platinum (Pt)
Type: Microetching
Method: Chemical etching
Etchant (electrolyte): 100 ml hydrochloric acid, 1-5 g chromium (VI)
oxide.
Procedu Seconds to minutes.
Remarks: Pure Au and Au-rich alloys. Pd and Pd alloys.
Reference: G. Petzow, Metallographic Etching, ASM (American Society
for Metals), 1978, p. 45.


As to the electro-etching of gold, yes, it certainly does work and is
widely used in the semi-conductor business. Unfortunately all the
recipes I've seen use cyanide compounds, particularly potassium
cyanide, and are therefore of little interest to me.

My own experiments on electrolytic etching of sterling silver have
been quite promising as they use only low voltages and common shop and
household electrolytes. I'm beginning to feel like a medieval
alchemist in my search for the same for gold.

Cheers,
Trevor F.