here light and not transparency is needed. You often
see it in office doors or in skylights of buildings. To get the
beautiful polished plate glass that you are talking about this rough
plate must be polished over and over again. But before it can be
polished it must first be annealed as rough plate. It goes into the
annealing ovens right from this table and comes out all irregular--full
of pits and imperfections. No matter how flat the casting table is, or
how much care is taken, the surface of the glass after annealing is
always bad. If it is to be made into polished plate it must be ground
down first with sand and water; then ground smoother still with a
coarse kind of emery stone and water; next ground again with water and
powdered emery stone. After that comes the smoothing process done with
a finer sort of emery and water. Last of all the sheet is bedded, as we
call it, and each side is polished with rouge, or red oxide, between
moving pads of felt."

"Goodness!" ejaculated Jean. "Do you mean to say they have to go
through all that with every sheet of plate glass?"

"Every sheet of _polished_ plate," corrected Giusippe. "Rough plate
does not need to be polished or ground down much. It is made merely for
use and not for beauty. Sometimes to add strength, and help support the
weight of large sheets, wire netting is embedded in them. Wired glass
like this was the invention of an American named Schuman and it is used
a great deal; the wire not only relieves the weight of the glass but
serves the double purpose of holding the pieces should any break off
and start to fall. Often, too, insurance companies specify that it
shall be used as a matter of fire protection."

"But I should think if plate glass--I mean polished plate," Jean
hurriedly corrected her error, "has to be ground down so much there
wouldn't be anything left of it. It must come out dreadfully thin."

"The casters have to consider that and allow for it," answered the
Italian. "They expect part of the glass will have to be ground away, so
they cast it thicker in the first place. A large, perfect sheet of
polished plate is quite an achievement. From beginning to end it
requires the greatest care, and if spoiled it is a big loss not only in
actual labor but because of the amount of material required to make it.
Even at the very last it may be injured in the warehouse either by
scratching or breaking. It is there that it is cut in the size pieces
desired."