Introduction
The history of English glassmaking divides cleanly into two periods: before George Ravenscroft, and after. Before Ravenscroft, English glass was made in the Continental tradition — light, fragile soda-lime glass in the Venetian manner, produced by immigrant craftsmen and broadly indistinguishable from the glass being made across northern Europe. After Ravenscroft, England had something entirely its own: a new glass of extraordinary brilliance, weight, and clarity, made possible by the addition of lead oxide to the glass batch, that would define English decorative art for the next century and a half and establish England as the pre-eminent glassmaking nation in the world.
Ravenscroft's invention was not a sudden flash of inspiration but the product of sustained experiment, commercial pressure, and considerable personal investment. Understanding the story of how lead crystal came to be — and what the earliest surviving examples look like — is essential context for any serious collector of English glass.
Who Was George Ravenscroft?
George Ravenscroft was born in 1632 into a prosperous Catholic merchant family with strong trading connections to Venice. He spent much of his early adult life in Venice as a merchant, and it was there that he developed both his knowledge of the Venetian glass trade and his understanding of the materials and techniques of Venetian glassmaking. When he returned to England in the late 1660s, he brought with him an unusually detailed knowledge of Continental glass production — knowledge that would prove the foundation of his subsequent experiments.
By the early 1670s, Ravenscroft had established a glasshouse at the Savoy in London, where he began a systematic programme of experimentation aimed at producing a glass that could rival or surpass the Venetian product. The Glass Sellers' Company — the London guild that controlled the English glass trade — was his principal backer and the commercial force behind his research. They wanted an English glass that could compete with imported Venetian glass, and they were prepared to invest in the research to achieve it.
The Problem with English Glass
The fundamental challenge Ravenscroft faced was the quality of English raw materials. Venetian glassmakers used a particularly pure form of silica sand from the Ticino river, combined with soda ash from the Levant, to produce their characteristic clear, light glass. English sand was less pure, and the available fluxes — the materials used to lower the melting point of the silica — produced a glass that was prone to cloudiness and impurity.
Ravenscroft's initial experiments in the early 1670s produced a glass that was clearer than previous English glass but still not entirely satisfactory. His early product was prone to a form of deterioration known as crizzling — a network of fine internal cracks caused by excess alkali in the glass batch — that the Glass Sellers' Company found unacceptable. The company complained formally about crizzling in Ravenscroft's glass in 1674, and Ravenscroft was obliged to continue his experiments.
The Lead Crystal Breakthrough
The solution Ravenscroft arrived at was the addition of lead oxide — specifically litharge, a form of lead monoxide — to the glass batch. Lead oxide served multiple functions simultaneously: it acted as a flux, lowering the melting point of the silica; it stabilised the glass chemically, reducing the tendency to crizzle; and it dramatically improved the optical properties of the resulting glass, giving it a brilliance, clarity, and refractive index far superior to anything previously achieved in England.
The resulting material — English lead crystal — was heavier than soda glass, softer and easier to cut and engrave, and possessed of a characteristic ring when struck — the clear, sustained bell-tone that became one of the defining qualities of fine English glass. It was also, crucially, stable: properly formulated lead crystal did not crizzle, and it retained its clarity and brilliance indefinitely.
By approximately 1675–1676, Ravenscroft had developed a sufficiently stable lead crystal formula to satisfy the Glass Sellers' Company, and in 1676 the company authorised the use of a raven's head seal — a small applied glass seal bearing an impressed raven's head, a punning reference to Ravenscroft's name — to mark glass produced to the improved formula. The seal was a guarantee of quality: glass bearing the raven's head had been produced to the stabilised lead crystal formula and could be sold with confidence.
The Raven's Head Seal: What It Means for Collectors
The raven's head seal was used from approximately 1676 to 1681 — the year of Ravenscroft's death — and possibly for a short period thereafter. It is found on a relatively small number of surviving pieces, applied to the bowl or stem of the glass as a small raised disc of glass with the raven's head impressed into it.
Sealed Ravenscroft pieces are among the most historically significant objects in English glass collecting. They are the earliest surviving examples of English lead crystal produced to a guaranteed standard, and they represent the direct physical evidence of one of the most important technological developments in the history of English decorative art. A sealed piece in good condition is exceptionally rare — the majority of known examples are in museum collections, principally the Victoria and Albert Museum, the Corning Museum of Glass, and the Fitzwilliam Museum in Cambridge.
For the private collector, the realistic prospect of acquiring a sealed Ravenscroft piece is limited but not entirely absent. Examples do occasionally appear at auction — typically at the major London houses — and when they do, they command very significant prices. The collector who encounters a purported sealed piece outside the major auction context should exercise considerable caution: the seal itself is the primary authentication point, and it should be examined carefully under magnification to confirm that it is applied glass with a clearly impressed raven's head design, not a later addition or a misidentified feature.
What Sealed Ravenscroft Pieces Look Like
The forms produced at Ravenscroft's glasshouse reflect the transitional moment of their production — they are neither fully Venetian nor yet fully English in character, but occupy a fascinating middle ground between the two traditions.
- Roemer forms — the roemer, a German and Dutch glass form with a wide bowl, cylindrical stem with applied raspberry prunts, and spreading foot, was one of the forms produced at the Savoy glasshouse. Ravenscroft roemers in lead crystal are among the most distinctive and recognisable of his productions.
- Posset pots and caudle cups — two-handled vessels for warm spiced drinks, reflecting the domestic drinking culture of the period.
- Jugs and decanters — serving vessels in lead crystal, sometimes with applied decoration.
- Drinking glasses — in forms transitional between the Venetian tradition and the emerging English baluster style.
The glass of this period has a characteristic appearance: slightly grey or smoky in tone compared to the clearer lead crystal of the early 18th century, reflecting the impurities in the raw materials and the not-yet-perfected formula. Some pieces show early-stage crizzling — evidence that even the sealed formula was not entirely consistent.
Ravenscroft's Legacy: The World He Made Possible
Ravenscroft died in 1683, two years after the raven's head seal ceased to be used. He did not live to see the full flowering of the tradition he had created. But the world of English glass that followed — the heavy balusters of the 1680s and 1690s, the light balusters of the early 18th century, the air twists and opaque twists of the mid-18th century, the cut glass of the late 18th and early 19th centuries — was entirely his creation. Without lead crystal, none of it was possible.
The heavy baluster glasses of the 1685–1710 period are the most immediate expression of Ravenscroft's legacy — forms designed specifically to exploit the weight, brilliance, and workability of lead crystal in ways that soda glass could never have achieved. Every collector of English 18th-century glass is, in a sense, collecting the consequences of Ravenscroft's experiments at the Savoy glasshouse in the 1670s.
Can Collectors Still Find Ravenscroft-Period Glass?
While sealed Ravenscroft pieces are effectively museum objects, glass from the broader Ravenscroft period — the 1670s and 1680s — does occasionally come to market, and the informed collector has a realistic prospect of acquiring examples.
- Crizzled early lead glass — pieces from the early period of lead crystal production, showing the characteristic crizzling of the unstabilised formula, are more commonly encountered than sealed pieces and are of considerable historical interest. Their condition is inherently compromised, but they are direct evidence of the experimental period of English glassmaking.
- Transitional forms — glasses in forms that bridge the Venetian and English traditions — roemers, posset pots, early drinking glasses with Venetian-influenced stems — from the 1670s–1690s period appear at specialist auction sales and with specialist dealers.
- Early heavy balusters — the finest heavy baluster glasses of the 1685–1700 period, while not Ravenscroft's own production, are the direct product of the tradition he established and represent the first great flowering of English lead crystal design. These are the most accessible point of entry into collecting the Ravenscroft era.
For the collector seriously interested in this period, the specialist glass sales at Bonhams and the stock of specialist dealers in early English glass are the primary sources. Patience is required — pieces of genuine quality from this period are rare — but the rewards, both aesthetic and historical, are considerable.
The Wonder Room occasionally offers early English glass of historical significance. Browse our current Georgian glass collection or explore further guides in Collector's Insights.