Pleased to say I have a reply from David Fogden - Clevedon Court - as follows:
""Dear Paul,
As the Administrator at Clevedon Court I necessarily hear a lot about the
house and its artefacts. Nevertheless, I am NOT an expert in glass!
The first thing to say concerns the term "Nailsea glass". I have attached
two of the sheets that we offer to our visitors and you can read about the
term there. I hasten to add that green glass must have been made all over
Europe. Our assertion about the origin of the green glass here, is merely
based on our location. As for whether your hat originated in Nailsea, who
can say?
Looking at the hats in our collection, nearly all have sharp edges where the
pontil was removed. None has been polished at all. We have always
understood that hats were apprentice pieces - presumably at many locations -
and perhaps there was no enthusiasm to do more with them once they were
complete.
There is a website that contains details of the National Trust collection at
http://www.nationaltrustcollections.org.uk/ If you search on "glass hat" you
can see the six hats that we have here.
Yours, David Fogden""
If you go to the website showing the NT collection of glass hats, I particularly like the tricorn example, and am happy to know there is at least another very similar to my pale green example. Do you recognize yours amongst them, Mike? I don't think we can say we're any further forward (and may never be) re knowing where specific types/colours were made, although the attached text sheets do seem to imply that simple plain and dark green friggers may well have originated at this factory, some with white or coloured chips - but apparently they never produced coloured glass.
In the attached text sheets, the brief history of Nailsea Glass Works is interesting - anyone know of 'The Nailsea Glassworks' by Margaret Thomas??
Just realized, being a bit of a thicky, that David's text sheets have been sent to me in pdf format, which the clever people will know are not compatible with the Board - so seems I cannot attach them. Is there a solution??