Mentions in literature:
Percy Bates wrote an article in 1905: An Eighteenth Century Industry: Bristol Enamel Glass.
E M Elville includes Bristol Glass in Paperweights and Other Glass Curiosities 1954 and later.
Moore 1935 in Old Glass European and American
Schwind, Arlene Palmer, Weeden, Cyril and Witt, Cleo (1984), "Bristol Glass": 94 pages 18 colour 28 b/w.
Witt, Cleo (1984), "Introducing Bristol Glass": 32 pages 8 b/w 18 colour.
Bedford, John (1964), "Bristol and Other Coloured Glass": 64 pages b/w colour.
Pountney, W. J. (1938), "A Short History of Bristol - Cut Glass": 8 page booklet 4 b/w.
But apart from those are no obvious specific references to Bristol blue. Bedford does debunk the myths in his book, perhaps someone has a copy of that to hand.
I suspect that this is just a folklore that has never been used in any serious study. It might be found in some of the Glass Encyclopaedia of course.