from The Century Dictionary and Cyclopedia
- n. In founding, a flask which holds the mold.
- n. Probably, a small box used like a casting-bottle.
Sorry, no etymologies found.
They are already bending it into a casting-box of the shape of the cylinders on the presses; metal will be poured in and when it is cool, you will have the metal form, the metal impression of the page.