Leni raised a couple of good questions:
When is it called 'upset muslin'? When it's all broken into pieces?
Actually, I think some of the terms used are interchangeable, so "lace" could possibly be also called "muslin" although the latter is usually of a much finer appearance and is "greyer looking" in antique French weights. "Upset muslin" looks like a mix bed of scrambled lengths and might also be called "tossed muslin".
What's it called when it's laid out in a criss-cross pattern?
Might be just "patterened" or perhaps "chequer board".
These terms seem to be just attempts to describe the look of the filigrana (or filigree, or latticino) as set in the weight. I don't know whether the terms (or equivalents) were used by the makers, but early sales catalogues such as 1950s Sotheby's certainly used many variations in their descriptions including "latticino", "white threads", "upset muslin", "chequer" etc.
[Maybe I could browse my books and catalogues to see how many different terms have been used and if there is a general consensus on any? Might be a way of filling in time during the lousy TV schedules over the next week or so.
And in relation to the obsolescence stated by CMG, Adam A added,
Abandoned by whom? The Corning Museum of Glass? Was this by decree and if so when was it published?!!
Yeah, I wondered that too. Maybe it was at about the same time that "lampworkers" became "torchworkers" in the US?