A very important advance in glass manufacture was the technique of adding lead oxide to the molten glass; this improved the appearance of the glass and made it easier to melt using sea-coal as a furnace fuel. This technique also increased the "working period" of the glass, making it easier to manipulate. The process was first discovered by George Ravenscroft in 1674, who was the first to produce clear lead crystal glassware on an industrial scale. Ravenscroft had the cultural and financial resources necessary to revolutionise the glass trade, allowing England to overtake Venice as the centre of the glass industry in the eighteenth and nineteenth centuries. Seeking to find an alternative to Venetian cristallo, he used flint as a silica source, but his glasses tended to crizzle, developing a network of small cracks destroying its transparency. This was eventually overcome by replacing some of the potash flux with lead oxide to the melt.
He was granted a protective patent in 1673, where production and refinement moved from his glasshouse on the Savoy to the seclusion of Henley-on-Thames.
By 1696, after the patent expired, twenty-seven glasshouses in England were producing flint glass and were exporting all over Europe with such success that, in 1746, the British Government imposed a lucrative tax on it. Rather than drastically reduce the lead content of their glass, manufacturers responded by creating highly decorated, smaller, more delicate forms, often with hollow stems, known to collectors today as Excise glasses. The British glass making industry was able to take off with the repeal of the tax in 1845.
Evidence of the use of the blown plate glass method dates back to 1620 in London and was used for mirrors and coach plates. Louis Lucas de Nehou and A. Thevart perfected the process of casting Polished plate glass in 1688 in France. Prior to this invention, mirror plates, made from blown "sheet" glass, had been limited in size. De Nehou's process of rolling molten glass poured on an iron table rendered the manufacture of very large plates possible. This method of production was adopted by the English in 1773 at Ravenhead. The polishing process was industrialized around 1800 with the adoption of a steam engine to carry out the grinding and polishing of the cast glass..