Chemistry Reference
In-Depth Information
excavations. Sometimes, only stains in the soil remain at the site where
ancient iron artifacts were once buried.
Slags
, the refuse of smelting, are,
however, practically indestructible; they consist mainly of a mixture of silica
and cinders of unburned charcoal. Iron slags are often found in large quan-
tities in archaeological sites, and the charcoal in the cinders can be mechan-
ically extracted and dated. Carbon in iron slag is therefore often used for
dating (by the radiocarbon method) iron-related operations, establishing
chronological sequences, and also as a surveying device in ancient iron-
smelting sites (van der Merwe 1969).
Gold
Pure
gold
(chemical symbol Au, from the Latin word
aurum
, for gold) is a
soft yellowish,
precious
,
noble metal
. Since it is a noble, inert metal, it does not
react with most chemicals and is therefore always found in nature in the
metallic state, as
native gold
. Moreover, gold is not affected by air pollutants,
as it neither tarnishes nor corrodes when exposed to the environment. Much
native gold occurs in quartz veins, sea gravel, or sand. From quartz veins it
was extracted in the past by
amalgamation
with mercury (see text below) or
by smelting and then refining, to obtain the gold in a high degree of purity.
From alluvial sands it was, and it still is, recovered by placer methods, such
as washing sand or gravel in a pan or dish: the gold particles remain and
are collected in the pan or dish, while the sand is washed out by the running
water. A quite detailed outline of the smelting process for the extraction of
gold from quartz veins by the ancient Egyptians in Nubia (the Land of Gold)
was written by the Greek historian Diodorus during the first century B.C.E.
He describes how gold-rich quartz was comminuted down to very fine par-
ticles that were then smelted together with lead. Cupellation of the raw lead
and gold alloy obtained from the smelting process removed the lead and
yielded pure gold beads, which remained in the cupel (Cauet 1999).
Gold is the most malleable of metals, as it is deformed by hammering
without breaking. It is because of its high malleability that gold can be made
into very fine sheets known as
gold leaf
, which has been used since early
antiquity for
gilding
other metals and wood and for illuminating manuscripts
(see below) (Shimura 1988; Nicholson 1981). Gold is also very
ductile
, and
can be drawn into wires without fracturing.
Gold thread
, made by winding
very thin and narrow strips of gold around a fibrous core of cotton, silk, or
other yarns, has long been used for making gold cloth (Járó 1990; Glover
1979). Gold and its alloys were widely used throughout the world even
before the dawn of history: gold jewelry (see Fig. 37) and ornaments
have been found in Stone Age tombs at many sites throughout the world.
