The Indiana State sentinel. [volume] (Indianapolis) 1868-1895, 1879-01-15
IRIDEsCENT GLASS.
What Causes Its Peculiar Character and
How 1t Is Made.


The Crockery and Glass Journal Says
Much of the old glass brought to light from
the buried cities of Pompeii and Hercula-
neuHa, from Roman tombs, and more re-
Gently from the treasures of the Cyprlote
cities or temples possess the curious prop
erty of iridescence. by means of which it re-
fleets light with all the colors of the rain
bow. There has been some dispute as TO
whether this glass was iridescent when made
or whether it acquired this quality subse
quently by some natural agency. The more
reasonable conclusion, and the one adopted
by Mr.. Peligot, the celebrated French chem
ist, is that the glass. originally plain, be-
came iridescent from long exposure to the
action of the air and moisture at a high tenn
perature, these conditions being admirably
fulfilled in the old Roman tombs where
most of the glass is found
All glass has tendency to become irIdes-
cent, under certain circumstances, but in
some kinds this tendency is more strongly
marked than in others. In glass for optical
instruments tendency to become iridescent
is a serious fault, and different kinds of
glass are combined to form a perfectly col
orless lens Modern chemists and glass
makers have long been trying to discover
the art of making glass irideecent by some
more speedy means than that of burying it
in damp soil for the benefit of a thank
less posterity. With all the progress made
in kindred branches of the art, nothing of
French chemists quite recently succeeded in
artifclally producing this iridescence The
process they make use of is said to consist
essentially in submitting the glass under
a considerable pressure and at an elevated
temperature TO the action of water con-
tanning fifteen per centum of hydro
chloric acid. Only certain kinds of glass are
suitable for this operation. The action of
this acid Is thought to be analogous to that
of the elements upon the older glass, in dis
solving the alkaline silicates and leaving the
surface Of the glass finely ridged or corrugat-
ed, and thus capable OF retracting the light
with prismatic or RAINBOW colors, like those
of mother of-pearl.
The modern glass stands any amount of
rubbing or cleaning without losing its Gu
rious property, but If the exposed surface be
cut or ground off, the iridescent effect is in
stantly lost, showing that its cause is merely
superficial, and not structural, as is the case
with mother-ofpearl.
The Bohemian glass; so far. seams to be the
favorite for embellishing with the new iris
descence. Bohemian glass will resist much
greater heat than any other kind, and is
made in graceful shapes, and is clear and
transparent. At present the leading Bohe-
milan factory is producing good deal of this
iridescent glassware, principally for the Eu-
rOpean market, as the American public is
hardly, as yet, acquainted with this novel
and beautiful glassware.
One of the greatest charms of this new
glass is its infinite variety and freshness No
two pieces are alike in color. and no piece
remains the same when placed in new posi-
ton or regarded from a different point OF
view. All show greater or smaller range
of the spectrum, curved or bent according
to the shape of the glass; but while some
pieces flash with red and yellow others are
tender with silvery blue or rich gold gray,
and still others exhibit all the colors of the
rainbow.