Manufacturer and builder 9 tai 10, 1869
Mr. Bechman, of Nuremberg, has succeeded in producing a metallic bronze of a blue color; the method of preparing which has hitherto been altogether unknown. He makes use of an alloy consisting of one hundred parts of pure tin, three parts of antimony, and one sixths part of copper. This is beaten out into thin leaves, which are converted into a brocade powder. The antimony should be free from arsenic, to secure which it must be remelted with nitre. The metals, after having been weighed out in the proper proportions, are fused in a crucible, under a layer of charcoal-powder. In beating the alloy, care must be taken that it be not heated too strongly, and to secure this, the form is laid aside after some blows.
The brocade, obtained from the metal leaves in the way indicated, is transferred into bottles having a wide neck, that can be well closed. Tissue are filled with water saturated with sulphide of hydrogen; two pounds of water being employed for every pound of brocade. The water ought to be completely saturated with the gas. Arseniferous substancei are to be rejected if a pure color be desired. The brocade, when in contact with the sulphurous water, is well shaken, in order that the fine leaves may become thoroughly moistened. After this, the bottles are well closed, and the shaking repeated at hourly intervals. After ten to twelve hours, the bronze appears of golden yellow. When it attains this color, the sulphureted water is poured offend replaced by pure rain-water; the brocade is then allowed to settle, and washed twice or thrice, so that the metal may be perfectly freed from the adhering sulphur-water. The powder is then dried upon paper in an ordinary drying-stove, such as is used by chemists. Only well washed and perfectly dry brocade assumes a pure blue. Adhering sulphureted water produces too dark a shade.
The proper color is produced by heating the yellow bronze, deposits itself in the following manner: When heated from 390 to 445° Fahr., it turns first dark yellow, then orange, then bright violet, then blue violet, and finally blue. If heated above the degrees mentioned, it catches fire, but without fusing, burning rapidly to an oxide. Heating can not be well effected over a charcoal fire, for the reason that, before the last bronze parts would exhibit the desired shade, those which had been turned blue first would probably be burned. Mr. Bechman therefore employs an oil bath, by which an equal heat is obtained. The arrangement consists simply of a pan for the reception of the bronze, that is set into a cast-iron kettle containing the oil. This may be rapeseed oil, mixed with a fourth part by weight of colophony, as pure oil does not yield the required heat. The bronze when taken from the fire is ready for use for all purposes, except for lithography, for which it must be slightly oiled.