The mold machine invented by the New England Glass Works revolutionized the flint glass industry. By its use glass could be pressed into any shape.

Glass in melted form is not malleable but its ductility is next to gold and by steady pressure can be forced into any shape. The mass blown against and into moulds was subjected to the stamp and penetrated the most delicate carvings. In places the early stippled specimens of Sandwich glass are only a thirty-second of an inch in thickness. The resulting sharpness of detail is wonderful.

The reason that nothing remains of the early molds is accounted for by the fact that iron was a costly commodity even as late as 1825. Thrift was responsible for the success of our forefathers and the glass molds which were made of soft tin were melted and re-run as they became dull from usage. Original designs were destroyed as new patterns were evolved. With the invention of the stamping machine iron ladles were used to pour the glass into the mold. We are often puzzled to know why a pontil should appear on early specimens of “pressed” glass. This is because the earlier specimens were actually blown against and into the molds before the invention of mechanical pressure.

Soft Slip, a clay used in making the old Connecticut slip ware dishes was run into a new mold. This proof showed any imperfections as well as supplying the works with a pattern for a new mold when necessary. These proofs were easily broken and of little use at the factory after a mold was discontinued.

A poor impression was caused by a worn out mold or as in the case of the very early plates made by plungers before the stamp machine came into use, by insufficient contact with the mold. The rarest type of Bunker Hill cup plate illustrates this point.

The carving of iron molds was called “Chipping” and mold chippers were responsible for the art of the finished product.

When the New England Glass Company moved to Ohio in the Eighties thousands of iron molds were sold to junk dealers.