the interior of the mass, no way of avoiding them having yet been
discovered. They are supposed to arise from the materials of the
pot and stirring rod, which become mixed in with the glass in
consequence of the intense heat to which all are subjected. These
veins must, so far as possible, be ground or chipped out with the
greatest care. The glass is then melted again, pressed into a flat
disk, and once more put into the annealing oven. In fact, the
operation of annealing must be repeated every time the glass is
melted. When cooled, it is again examined for veins, of which
great numbers are sure to be found. The problem now is to remove
these by cutting and grinding without either breaking the glass in
two or cutting a hole through it. If the parts of the glass are
once separated, they can never be joined without producing a bad
scar at the point of junction. So long, however, as the surface is
unbroken, the interior parts of the glass can be changed in form
to any extent. Having ground out the veins as far as possible, the
glass is to be again melted, and moulded into proper shape. In
this mould great care must be taken to have no folding of the
surface. Imagining the latter to be a sort of skin enclosing the
melted glass inside, it must be raised up wherever the glass is
thinnest, and the latter allowed to slowly run together beneath
it.

[Illustration with caption: THE GLASS DISK.]

If the disk is of flint, all the veins must be ground out on the
first or second trial, because after two or three mouldings the
glass will lose its transparency. A crown disk may, however, be
melted a number of times without serious injury. In many cases--
perhaps the majority--the artisan finds that after all his months