noun: mould; plural noun: moulds; noun: mold; plural noun: molds
a hollow container used to give shape to molten or hot liquid material when it cools and hardens.
"the smith would pour the molten metal into the shaped mould"
synonyms: cast, die, form, matrix, shape, container;
framework, template, pattern, frame
"the molten metal is poured into a mould"
"a pudding or savoury mousse made in a mould"
"a lobster mould with a sauce of carrots and port"
a distinctive and typical style, form, or character.
"he's a superb striker in the same mould as Gary Lineker"
synonyms: character, nature, temperament, temper, disposition, cast/turn of mind, mettle
So what the sentence seems to mean: it was of a form/shape that is no longer in use ('lost'). Glass is not actually 'moulded' (1st definition), but I think the author's choice is more in line with the second meaning (derived from the first one, probably).