Hi Ian and Wuff
I researched the ST and Y weights and the resulting article appeared the Paperweight Collectors Circle magazine issue 95
dated Dec 2007, with some further research documented in issue 97 August 2008 and an article on the Broughton collecton in issue 96 April 2008.
The St Tudy paperweight centre moved from St Tudy to Yelverton in 1978 but Bernard Broughton the founder continued to call it the St Tudy paperweight centre for some years as he wanted visitors to know that the centre had moved to Yelverton and that this was not a new centre that had opened up in opposition to the St Tudy centre. 1979 is the latest date known for an ST embossed weight and the earliest Y embossed weight is 1981.
There were two basic designs for the ST and Y embossed weights. The one mentioned here with the piece of quartz and also an abstract swirl weight both styles have numerous colourways. They were all numbered and I was shown a certificate that came with each weight in the first run which was made at Liskeard. This showed that the run was 500 although it is likely that they would have been delivered to the paperweight centre in smaller called off batches. The second run which possible ran to 1000 pieces was produced by the Isle of Wight Studio Glass (IOWSG) in 1976. Incidently, according to one ex-worker at the St Tudy centre, Bernard wa a very astute business man and to maximise the profit margin he used to take his family onto Bodmin moor to collect suitable pieces of quartz for encasement
There were several runs after 1976 and there is evidence to show that both studios produced further batches, but which studio produced which batch is not known. Although I have no documentation to prove it it seems almost certain that both styles were produced at both locations. Certainly there are examples of both styles embossed ST 1976 made at IOWSG and two IOWSG employees Keith Pollard and Peter Riley said that they recalled several production runs.
There is also a link between the two studios. Liskeard Glass was founded by Dr. John Randall in 1973 but he sold it to Tim Bristow in 1978 who was a glassworker at IOWSG. Tim subsequently sold Liskeard Glass to one of his craftsmen Liam Carey in 1983 and returned to IOWSG. Liam renamed Liskeard Glass to Merlin Glass and it has continued to trade under this name with Liam at the helm to the current day.
As a matter of interest Bernard Broughton commissioned paperweights from a number of other makers - John Deacons, Perthshire and Selkirk (Peter Holmes) are all known to have produced more elaborate examples in smaller runs and with ST and Y signature canes rather than the embossed ID's.
Hope this helps