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Book IX artificially coloring of metals such as gold, silver, copper

Book VIII metals, precious such as gold, platinum, silver Page of 251 Book IX artificially coloring of metals such as gold, silver, copper Text size:minus plus Restore normal size   Mail page  Print this page
BOOK IX
Nature may tint metals with a color that is foreign to them. The true color of copper is red yet sometimes it occurs yellow. The Greeks call this όρβίχαλκος. Sometimes copper is white and this is called \f/ev8apyvpos. The latter has the appearance of silver, the former the appearance of gold. Pliny writes that the yellow copper has a characteristic and pleasing beauty by day. Strabo writes that the white copper was made in Teu-thrania near Andera and in Lydia near Mt. Tmolus. Copper can be colored artificially to imitate nature.
Native cadmia1 is added to copper to make brass (orichalcum). Accord­ing to Pliny at one time Livian copper was used chiefly in making brass and later, Marian copper. Brass is made in the following way. Alternate layers of the best broken copper and cadmia are placed in a tall crucible. When it is full it is lowered into a furnace in a space that has been hollowed out and is fired as if it were in a covered passage. When entirely melted, the copper is changed into brass with the color of gold. This is the com­mon method. By another method sheets of copper three-quarters of an inch wide are placed in a crucible similar to those used in casting silver but having the outside covered with a clay containing iron scale and the inside covered with the most highly refined honey. The thin sheets of copper are also coated with honey. They then sprinkle over the copper a very fine powder consisting of native calamine, dry dregs of wine that they call tartar (argol) and charcoal in equal amounts. The crucible is covered with an earthenware lid with a hole in it. A rod is thrust through this hole and used to stir the molten copper. The lid is sealed to the crucible with the above mentioned clay. The crucible is then placed in a furnace similar to those used in a mint. When the calamine mixes with the copper it first gives off a red flame, then a flame that is part red, part blue and finally a yellow flame that indicates the mixing is completed. Then the crucible is removed from the furnace.
They make many things from brass but most commonly basins, candel­abra, lichnuches, and siphons. These articles are more valuable when made from brass than from copper since they have the same hardness and a more pleasing golden color. Brass, like copper, can be whitened with powdered gypsum that occurs in crusts until it has the appearance of silver. Copper so whitened is pleasing and esteemed and for that reason is made into goblets. Copper is also whitened in the following manner.
1 The literal translation is calamine. This name is given in the United States to the natural hydrous zinc silicate and in England and Europe to the natural zinc carbonate. To eliminate this confusion it has been proposed to use the name cala­mine for oxide zinc ores in general and call the carbonate smithsonite, the silicate hemimorphite. Under cadmia Agricola included not only the natural zinc oxide minerals but also artificial oxides.
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Book VIII metals, precious such as gold, platinum, silver Page of 251 Book IX artificially coloring of metals such as gold, silver, copper
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