THE MUSEUM. 



!79 



mourning jewelry, is so prepared. In 

 the banded varieties, some of the 

 bands are more absorbent than others, 

 and thus the highly colored black and 

 white onyx and red and white sardonyx 

 are produced, and most of the richly 

 tinted variegated agates used for orna- 

 mental work. Picture agate is the 

 name given to quaint markings resem- 

 bling human forms or like- objects. 

 The famous Madonna agate in the 

 \'ienna collection has thousands of 

 peasant visitors annuUy. 



Moss agate has been much less used 

 during the past twenty years than for- 

 merly, the annual sales not exceeding 

 $ 1,000. Since the recent use in cheap 

 jewelry of the Chinese natural green 

 and artificially colored red and yellow 

 moss agate, the sale of the American 

 has greatly fallen off. At Hartville, 

 Wyo., large masses of moss agate, 

 weighing from forty to fifty pounds 

 each, were recently found in limestone 

 rock. When cut into translucent 

 slabs, they show the magnificent black 

 dendritic or moss-like markings in a 

 most striking manner. Some table 

 tops of this elegant material were ex - 

 hilsited in the Wyoming section of the 

 Mining building at the World's Colum- 

 bian Exposition. The finest instruc- 

 tive collection of agate known is the 

 wonderful series presented to the Har- 

 vard mineralogical cabinet by Dr. W. 

 S. Bigelow of Boston. Ruskin wrote 

 upon and presented a fine series of 

 agates to the British Museum. 



If chalcedony is boiled in a solution 

 of molasses and water, blood and 

 water, or sugar and water, until it has 

 absorbed a quantity of the solution, 

 and is then again boiled in sulphuric 

 acid, the transparent hydro-carbon is 

 changed to a charcoal substance, and 

 black onyx is produced. When white 

 bands alternate with the chalcedony, 

 they are impenetrable to the coloring, 

 and appear clearer and brighter. 

 Black onyx has now almost entirely 

 superseded jet. 



The yellow variety is made by first 

 putting the stones in a honey solution. 



then in a solution of chromate of lead 

 for several days. Placed for a few 

 weeks in hydrochloric acid at a moder- 

 ate heat, a beautiful cleat yellow glow 

 is given to the streaks that were be- 

 fore a dirty brown. This is also erron- 

 eously called golden opal. Stones of 

 a reddish hue are greatly improved in 

 brilliancy of color by first thoroughly 

 drying them for weeks in ovens, then 

 dipping them in sulphuric acid, heat- 

 ing to full red hhat, and afterward 

 slowly cooling them. The changes 

 that take place in both these processes 

 are upon the oxide of iron, which is 

 the coloring matter. 



Modern chemistry has wrought great 

 changes in agate coloring, as in other 

 arts, a secret process having be en 

 discovered by which chalcedony of any 

 single color can be made to assume 

 any two or more colors, so that an 

 onyx of any shade or variety of colors 

 can be made. If a sunken centre of 

 another color is required it can be 

 made so that the figure wnen cut out 

 remains in a hollow, forming a cameo 

 intaglio. In this manner the fine cut- 

 ting of the cameo is protected. A 

 white figure may be made in a black 

 stone, a red figure in a brown stone, 

 or a white one in a red stone. By 

 this process the entire stone is first 

 changed to the color desired for the 

 outer layer, then a cavity is cut in the 

 top and a solution put into it, which 

 alters it to the desired color. It is 

 this discovery that has made a former- 

 ly valuable onyx worth now only a 

 nominal sum. 



Agates are thus made to assume the 

 onyx character, which is desired by 

 the lapidary, for the production of 

 cameos and intaglios in imitation of 

 the antique sculptural gems. In cam- 

 eos the figures are in relief and of a 

 different color from the ground. In- 

 taglios are usually all of one color. 

 In Persia inscriptions or devices are 

 written on beads of carnelian and oth- 

 er forms of agate with carbonate of 

 soda and other chemicals; they are 

 then burnt, and the inscription ap^ 



