This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
A vast number of articles, chiefly small in size and of a more or less artistic character, are cast in brass, bronze, or one of the many modifications of these well-known alloys.
Pure copper is moulded with difficulty, because it is often filled with flaws and air-bubbles, which spoil the casting; but by alloying it with a certain quantity of zinc, a metal is obtained free from this objection, harder and more easily worked in the lathe. Zinc renders the colour of copper more pale; and when it exists in certain proportions in the alloy, it conmiunicates to it a yellow hue, resembling that of gold; but when present in large quantity the colour is a bright yellow; and, lastly, when the zinc predominates, the alloy becomes of a greyish white. Various names are given to these different alloys. The one most used in the arts is brass, or yellow copper, composed of about 2/3 of copper and 1/3 of zinc. Other alloys are also known in commerce, by the names of tombac, similor or Mannheim gold, pinchbeck or prince's metal (chrysocale), etc.; they contain in addition greater or less quantities of tin. Tombac, used for ornamental objects which are intended to be gilded, contains 10-14 per cent. of zinc; the composition of Dutch gold, which can be hammered into very thin sheets, being nearly the same. Similor, or Mannheim gold, contains 10-12 per cent. of zinc and 6-8 of tin; and pinchbeck contains 6-8 per cent. of zinc and 6 of tin.
If brass be heated in a brasqued crucible in a forge-fire, the zinc is nearly wholly driven off. Brass is made by melting directly copper and zinc; rosette copper being used, fused in a crucible, and run into water to granulate it. The zinc is broken into small pieces. The fusion is effected in earthen crucibles which can contain 30-10 lb. of alloy, the metals being introduced in the proportion of 2/3 of copper and 1/3 of zinc, to which scraps of brass are added. Small quantities of lead and tin are frequently added to brass to make the alloy harder and more easily worked; brass which contains no lead soon chokes a file, which defect is remedied by the addition of 1 or 2 hundredths of lead.
Copper and tin mix in various proportions, and form alloys which differ vastly in appearance and physical properties, as tin imparts a great degree of hardness to copper. Before the ancients became acquainted with iron and steel, they made their arms and cutting instruments of bronze, composed of copper and tin. Copper and tin, however, combine with difficulty, and their union is never very perfect. By heating their alloys gradually and slowly to the fusing point, a large portion of the tin will separate by eliquation, which effect also occurs when the melted alloys solidify slowly, causing circumstances of serious embarrassment in casting large pieces. Different names are given to the alloys of copper and tin, according to their composition and uses: they are called bronze or brass, cannon-metal, bell-metal, telescope-speculum metal, etc. All these alloys have one remarkable property: they become hard and frequently brittle, when slowly cooled, while they are, on the contrary, malleable when they are plunged into cold water, after having been heated to redness. Tempering produces, therefore, in these alloys an effect precisely opposite to that produced on steel.
When alloys of copper and tin are melted in the air, the tin oxidizes more rapidly than the copper, and pure copper may be separated by continuing the roasting for a sufficient length of time.