The daily morning journal and courier., 1898-09-22

fidelity with which the details of the design are revealed are beyond ques- tion, but it may be doubted whether the surface of the medal Is permanent ly protected. A medal with frosted platernized surface has, however, a great advantage over one with pol ished table, as the platinized medal is merely deepened in tone by exposure to the atmosphere and, unlike medals which have been struck in the ordinary way, does not become disfigured by blotches of tarnish. The frosted plati- nized medal may be restored to almost it's original freshness by careful rub ping with soft leather. while pol fshed silver one cannot be so renovated, as the tarnish attacks the surface and destroys the polish.
 During the last year. for the first time in the history of the British mint, med als have been issued with frosted and platinized surfaces More than twenty seven thousand large silver medals were platinized by slight modification of the above It became necessary, there fore, to provide an appliance for pro- ducing the sand blast, and this, togeth- VI Wilil eb Silicill OilS HUI pOWSl ihoboh for driving it, has been fitted up in the basement of the assay department.
 Medals of bronze differ considerably from those of silver, as their surfaces are far more liable to be influenced either by the slow operation of the con- stituents of the atmosphere or by the more rapid action of chemical agents. Ancient silver coins, for instance, which have been long buried in the earth 60 not show anything like so wide q range of color in their patina or crust as is revealed on coins of brass. bronze or copper which have been hid den in the same way. This is due to the fact that silver is far less affected than copper by the chemical action of the constituents of soils or by atmos- pheric influences.
 The patina acquired by an ancient coin or medal often constitutes no small part of it's value. You would laugh at me-" said Philander, in Addison's charming dialogues upon the useful ness of ancient medals, should I make you a learned dissertation on the na- ture of rusts; shall only tell you that there are two or three sorts of them which are extremely beautiful in the eye of the antiquary, and preserve a coin better than the best artificial var nish." The object of the medallist is accurately expressed in the above sen tence, for he endeavors to protect the surface of all medals in which copper is the main constituent by patina or film of oxide, so as to preserve the med- al from further change. This may be effected in various ways. The medals of the Italian Renaissance were not struck, but cast by the method of cera perduta, and much of the beauty of the medal was due to the skin or pellicle of oxide which the medal acquired dur ing casting. The skill of the artist in arranging the composition of the bronze and fixing the temperature at which it was cast was revealed in the texture of the medals surface.
 In modern times most medals to which the name of bronze is given are really of copper "bronzed" or colored artif1cially on the surface The process by which this coloring is effected has long been employed, and is thus de- scribed in an old recipe: Rpply with a brush to the surface of the medal com mon crocus powder, jewellers rouge, previously made into a smooth paste with water. When dry expose the med al over clear fire for about one nin- ute; lastly, when the medal is sufficient ly cold. polish 1t with q plate brush. The exact composition of the superf- cial layer of oxide which is formed has, I believe, never been ascertained; but 1t is well known that the tint varies greatly from light brown to deep choco- late, according to the particular variety of oxide of iron which is used.
 With a view to ascertain whether this old method could not be replaced with advantage, it was natural to turn to the work of Japanese artists, who are mas ters in the art of giving protective sur faces of varied tints either to copper in it's pure state or to copper alloys. l have shown elsewhere that in conduct ing such operations the Japanese em- ploy dilute boiling solutions of certain salts of which verdigris and sulphate of copper are the more important
 The following solution has been found | to answer fairly well, even when the
 ordinary European verdigris, which is a
 basic acetate of copper, is employed: Verdigris .......................8 grains. { Sulphate of copper. .437 grains ! Nitre .......,............... S7 grains l Common salt. 6S grains l Sulphur 233 grains | Water ...................... i gallon [ In Japan, however. "verdigris" Is I made by the action of plum juice vine i gar on plates of copper which contain | certain metallic impurities. Such na-
 tive verdigris has consequently a very
 complex constitution. It is called 'rok-
 asho," and cannot be procured in this
 country; but I am indebted for sam-
 pie of it to w. Gowland, formerly tech
 nical adviser to the Iananese mint al