period - Author's Note.), although there is no certain reference to it in
the description of the objects. The reddish-brown colour gives the test
for iron, silver and copper, and is evidently due to iron and copper in
the gold that have oxidized. In some instances a red or purple colour
proved to be a staining of the gold by organic matter, since it was not
soluble either in acids or in organic solvents, but could readily be
removed by heating. The rose colour can be proved by chemical analysis
not to be due to any colloidal modification of the gold, nor to any sort
of organic lacquer or varnish, and the gold can be made red-hot without
the colour being removed or diminished, but in some instances rather
enhanced. The coloured film, however, is so extremely thin, being probably
less than one hundred-thousandth of an inch in thickness, that without
more material than it is advisable to use, chemical analysis becomes very
difficult. A trace of iron is the only metal found so far, and since it
is well known that native gold is sometimes reddened by being coated with
a translucent film of oxide of iron, it is suggested that the colour in
(August 30, 2008)
Back to Gold (TAA i.3.14).