A few years ago I mixed up some purple gold: 79 Au + 21 Al. It
was an expensive experiment where most of the gold seemed to
vanish. However I did wind up with a little nugget encrusted with
a crinkly gold coating.
The nugget was hard as a rock. When cut open with a separating
disc the interior was composed of the most incredible color of
gold imaginable: a rich bright purple. I have since learned that
this is not a true alloy, but an “intermetalic compound,” because
the two metals do not mix. It is totally unworkable as a metal,
but can be carved with lapidary-type equipment.
Revere Academy of Jewelry Arts