VITREOUS COLLECTION. 
331 
have been enclosed in a mass of glass the product can be readily 
formed into tazze or vases as shown in the finished examples in 
Oase 66. 
Some very line examples of modern engraving on glass will 
also be found here. The ordinary tools used in engraving glass 
are discs of copper, smeared with oil and emery and worked by 
a lathe. 
Attention may here be directed to the specimens of Aventu- 
rine glass, made at Murano and largely used in cheap jewellery. 
The brilliant laminae are particles of metallic copper, showing 
under the microscope beautiful crystalline forms. Here, too, is 
a large series of artificial gems made of strass. 
Strass , so called after its inventor, is a glass possessing in 
the highest degree purity and transparency, combined with the 
greatest possible lustre. It is a mixture of quartz, boracic acid, 
purified caustic potash, and a large proportion of oxide of lead, 
introduced in some specimens of strass as red lead, and in others 
as white lead. With perfectly pure and colourless strass, the 
colouring agent is combined — the following being a few 
-examples : — 
Topaz, antimony and gold ; Ruby, purple of Cassius ; Emerald , 
oxide of copper or chromium ; Sapphire, oxide of cobalt ; Ame- 
thyst. cobalt and gold ; Beryl, antimony and oxide of cobalt ; 
Garnet, gold, antimony, and manganese ; Opal, bone ashes, oxide 
of uranium and forge scales, or, in some cases, oxide of nickel. — 
{Knapp.) 
At an early period the practice of making hollow glass beads, 
and filling them with a pearly varnish, was adopted. Artificial 
pearls were thus made by some artists at Murano, but the 
government of Venice considered the invention too fraudulent 
and prohibited its practice. 
A French bead maker, Jaquin, revived and improved the art. 
He observed that the bleak ( Gyprinus alburnus ) when washed 
in water gave off numerous fine silver-coloured particles which 
had the lustre of the most beautiful pearls. He consequently 
scraped off the scales of the fish and called the pearly powder 
which was diffused through the water, essence a orient, or 
essence of pearl. At first he covered beads of gypsum with this, 
but as the ladies who wore them found the pearly powder left 
the beads and adhered to the skin the use of those ornaments 
fell off. The beads were then made of glass, a glass easily 
melted and made a little bluish, being drawn into tubes which 
were called girasols (the word signifying opal). From these 
tubes hollow globules were blown, and they were then covered 
on the inside with a solution of isinglass and the pearl essence, 
which was blown in warm and spread over the internal surface 
by rapid motion. When dry, the globules were filled with wax, 
bored through with a needle and strung as beads. 
