MECHANICS AND USEFUL ARTS. 77 



quantity of flux; thus, when the picture is fired, the flux of the plate unites 

 with the flux of the color, and the coloring pigment is perfectly excluded 

 from the air by being surrounded by a dense vitrified mass. From this will 

 be understood the indelible and we might almost say eternal nature of 

 enamel. 



" The plate undergoes the process of firing after each layer of color is 

 spread over the whole surface. This process corresponds to the drying of 

 the pigments in oil or water-color painting before the artist ventures to 

 retouch his work. Sometimes highly-finished enamel requires fifteen or 

 twenty firings. Great care must be taken to paint without errors of any 

 kind, as the colors cannot be painted out or taken off, as in water or^il, 

 after they have once been vitrified, without incurring excessive trouble and 

 loss of time. If the unfortunate artist miscalculates the effect of the fire 

 on his pigments, his only alternative is to grind out the tainted spot with 

 pounded flint and an agate muller; and so hard is the surface, that a square 

 inch will probably take him a whole day to accomplish." 



THE IVORY TRADE. 



The principal source of supply of ivory is Africa much of it coming 

 from the interior by way of Egypt and the Nile. Until within a few years 

 the Egyptian pashas made trading up and clown the Nile a monopoly ; now, 

 Egyptian, French, German, and English merchants explore the remote re- 

 sources of the river, not for the purposes of science, but for those of com- 

 merce. In the last report of sales of ivory in London, the head-quarters of 

 this traffic, we find that eighty -five thousand pounds of the ivory sold was 

 " Egyptian ; " that is, found its way to civilization through Egypt. 



That Africa was the source whence the ancients of southern Europe drew 

 their supply, we learn from Pliny the Younger, who says that the vast con- 

 sumption of ivory for articles of luxury compelled the Romans to seek for it 

 in another hemisphere, " as Africa had ceased to furnish elephants' tusks 

 except of the smallest kind." 



After the overthrow of the Roman Empire, the commerce between Europe 

 and Africa was suspended for centuries. At length the enterprise of Portu- 

 gal, the eldest daughter the Lusitania of Rome, opened anew Africa and. 

 India. In the meantime, the lordly elephant had multiplied in his native 

 forests, and if the long tusks were secured by the natives, they served merely 

 the plebeian purposes of door-posts, or the defences of wooden idols. Battell, 

 a quaint old Englishman, who served in the early Portuguese armies, says 

 that the Africans "had their idols of wood, fashioned like a negro, and at 

 the feet thereof was a great heap of elephants' teeth, containing three or four 

 tons of them." It is a well-known fact that the inhabitants of Angola and 

 Coniro, when the Portuguese first occupied those coasts, were found to have 

 preserved an immense number of elephants' teeth, the accumulation of cen- 

 turies. For a long time this ivory was exported in vessels of Portugal to 

 various parts of Europe ; and this traffic formed one of the most lucrative 

 branches of the early modern trade with Africa. About the middle of the 

 seventeenth century this store became exhausted, and the sons of Ethiopia 

 were instigated to imitate their ancestors in renewing the battle with the wide- 

 eared, long-tusked Elephas Africamis. 



To-day, the amount of ivory consumed in the workshops of Europe, 

 America, and India, is immense; and yet, great as it is, the continent of 



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