I believe the answer is yes; (FeCl) Ferric Chloride will etch
Shakudo (assuming it is the traditional Mokume [4-5% Au + the rest
Cu] 95% copper). It will appear kind of pink with a purplish tinge
in it's natural state.
A good reference book is published by Krause Publications the title
is " Mokume Gane" the author is Ian Ferguson the ISBN 0-87349-901-8.
By Ian Ferguson
Manufacturer : Krause
Release data : 15 June, 2004