At some point during the mid to late 1700s - it is not clear exactly when - the opportunity arose in Bristol to manufacture cobalt-blue glassware.

One theory suggests that the marked expansion of cobalt glass in Bristol stemmed from the experimental activities of William Cookworthy (1705-1780), a pharmacist and china manufacturer, based in the South West of England, who imported high quality cobalt oxide from Silesia (now Germany).

Cookworthy used the cobalt oxide in the decoration of his porcelain ware, much of which was painted in underglaze cobalt blue, both at his factory in Plymouth, and later, when he moved the factory to Bristol (around 1770). Cobalt oxide is a versatile product: when added to lead glass, the colour that emerges is a deep, rich, distinctive blue.

The theory goes that Cookworthy obtained exclusive import rights to all the cobalt oxide from the Royal Saxon Cobalt Works at Schneeberg. Since he shipped it to England through the port of Bristol, Bristol glassmakers had the best access to it and used it extensively in the decoration of their products - hence the purported origin of the term 'Bristol Blue'.