Chemistry Reference
In-Depth Information
America and ancient Rome. The Romans, for example, used the dipping
technique to give copper the brilliance of gold. The
dipping
process entails
two successive working stages: (1) heating under reducing conditions (to
prevent oxidation of the surface of the object to be gilded) and (2) dipping
the hot object for a short while in a bath of molten gold or one of its alloys
at a temperature lower than that at which the base metal melts. The molten
gold or gold alloy thus wets and covers the object with a thin layer that, on
removal from the bath and cooling, solidifies as a well-attached gilding layer
(Scott 1983; Bergsoe 1937).
Gold Thread.
Metal threads
are thin threads of one of the precious metals,
mostly gold but also silver, which are employed to make highly decorative
textiles known as
gold
and
silver cloth
. Most used in antiquity to make gold
or silver cloth were two types of metal threads: (1) very thin strips of a pre-
cious metal; (2) composite threads, made by winding very thin, narrow strips
of a metal around a fibrous core of cotton, silk, or other yarn (Járó 1990;
Lee-Whitmann and Skelton 1984). Gold and silver cloth (woven or decorated
with metal threads) have always been identified as symbols of wealth and
opulence and are among the most admired and precious antiquities. Only
during the late twentieth century, when the spread of inexpensive, precious-
metal-appearing threads and mechanized textile decorating methods
became easily available to all, did the interest in textiles decorated with
precious metal threads decrease.
Silver
Silver
(chemical symbol Ag, from the Latin word
argentum
, silver) is a light
gray, highly ductile, malleable, and very soft precious metal. The softness of
silver makes the pure metal impractical for many applications. Some alloys
with copper contain between 80% and over 90% silver and are much harder,
and therefore such alloys have been used for most applications. As with the
alloys of gold, in everyday usage the alloys of silver and copper are gener-
ally referred to as
silver
. Neither the metal nor its alloys are oxidized when
exposed to the atmosphere; they easily react, however, with hydrogen
sulfide, an air pollutant, forming a dark gray and a esthetically impairing
surface layer known as
tarnish
(composed of silver sulfide) (see text below).
Native silver
is rarely found in the form of nuggets, and it is probably for
this reason that silver was recognized and came into widespread use at later
times than did gold. Much native silver occurs as minute grains dispersed
in small concentration in
argentiferous
(silver-rich) sands. Now, when silver
is mixed with mercury, it forms
amalgams
(see below); the
amalgamation
