106 ROMAN MOSAIC. 



vantage of being uninjured by damp, lime, and all the various 

 causes by which painting is destroyed; and when we view 

 the magnificent copies of the old masters which decorate St. 

 Peter's, we cannot but value an art by which so many fine 

 works are perpetuated, which otherwise would be lost to suc- 

 ceeding ages. 



HENRIETTA. 



In, what manner do they work at it? 



MRS. F. 



A slab of marble or stone is taken, out of which the artist 

 cuts the space which he intends to fill, and encircles it, for 

 strength, with bands of iron. He then covers this space with 

 a thick layer of mastic, in which he places his pieces of glass, 

 according to the design which he is copying. When the 

 subject is finished, it is all ground down to a level surface, 

 and then polished. 



ESTHER. 



I suppose, mamma, when you were at Rome, you saw the 

 Roman pearls made. 



MRS. F. 



Yes; for I always make a point of seeing the manufactures 

 of every country which I visit. The Roman pearls differ in 

 their composition from those made in France, the latter being 

 glass beads filled with wax and coated with the silvery sub- 

 stance obtained from the scales of the Bleak (Cyprinus 

 alburnus'). 



HENRIETTA. 



Then how are the Roman pearls made? 



They are formed of the purest alabaster, which comes 

 principally from the neighborhood of Pisa. The alabaster 

 is sawn into slices, the thickness of which is equal to the 

 intended diameter of the pearl. The pearl is then made by 

 an instrument which works something on the principle of the 



