Just some thoughts:
1) Hajdamach says on page 82
'
The earliest English designs for cased glass appear in the Richardson pattern books about 1844 (Plate 57). ... At the Manchester Exhibition of 1845-1846 Richardson's displayed blue, green and red cased glass described as 'laudable attempts to rival the produce of Bohemia' (Plate 59).'
I don't know who wrote the report about the Manchester Exhibition, however Bohemian cased glass of that period and earlier included triple overlay items (See Farbenglas 1 page 111 for examples dating to 'before 1837') and was imho incredible in it's production and execution and colours. So is the word laudable is doing a lot of heavy lifting in that reporters comments? For example at the Great Exhibition in 1851 the reporters were still commenting on how English coloured glass was not as good as Bohemian coloured glass.
Anyway, my point is that for it to have been by Richardson date wise it is likely to have been post about 1844.
2) Bohemian glass of the later decades was still using the traditional methods of cutting and faceting handles and shapes so dating them by those attributes alone would be difficult. The whole object, it's base, it's rim, the colour, the design of the shape and the design of the pattern cutting need to be taken together in the round.
I have seen cased Bohemian glass with a large polished pontil on the base dating to c.1850s/60s. Annathal used a large polished pontil mark as did Buquoy. I have two pieces which are triple overlay and definitely Bohemian. They date to 1850/1860 and have a large polished pontil mark on the base. Also a perfume bottle, Bohemian probably Steinschonau that dates to c.1845 that has a large polished base and a polished pontil mark.
It's not that easy to pin these things down.
3) The colour - it's amethyst:
This information from Spiegl W - Glas-forschung 'Farbige Gläser' on page 25 discusses the difficulty of working with amethyst glass.
http://www.glas-forschung.info/pageone/pdf/farbglas.pdfI wonder then if perhaps your jug was made in a period when amethyst was being supplied ready made to be used? Using ready made colours? I can't quite remember how they work but there was a move from makers making their own colours in the batch, to using ready made colour at some point in the mid 1800s if I recall correctly.
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