PERIOD

WINDOW GLASS

GLASS TYPES AND MEASURES

AN IRISH PERSPECTIVE

Nessa Roche’s history of the Irish market for glass closely mirrors English practice but with some specific local differences.

This information comes from research being carried out into the development of window types and window glass in Ireland. Bothtookasimilarformtothatin Britain. Glassmaking and importation are covered in the research, which has thrown up some interesting facts on the types used and the measures and quantitieswhichwere standard. Glassmakers in Ireland were almost exclusively foreign, and importation was far more common than domestic production, so the informarion listed here will be relevant to Conservation Officers and others in Britain who may come up against some of the obsolete terminology in old documents and building accounts. A very informative book is that of Richard Neve - The City and Country Purchaser, 1703. Each glass type had a different measurement of square footage per case, cribb, chest, basket, way or webb. Here the types of glass, with description if known, aregiven, andthe differing quantities and measures are listed at the end.

TYPES

Two main types of glass were manufactured before the 19th century, both blown, of which panes are commonly found in old windows and need to be treated with the greatest of care.

Broadgiassisgenerallytermed ‘white’; a blown cylinder was formed, and when cooled, adiamondusedto cutthe cylinder along its length. This was heated and the cut cracked. When the cylinder was hot and the glass fluid, the opened cylinder was helped to flop down flat onto a sanded surface (refinements in manufacturemeantthatthecuttingandlaying out could be done in one operation, makingthewholeprocessmuchquicker).

The characteristics of this glass are a pocked surface, with streaks from the timberbattens used to flatten it. After the introduction of crown, broad glass quickly became the second choice, used in the main for quarried glazing.

Crown glass was perfected (or invented) by London glassmakers in the late 17th century, and it had a crucial advantage

over broad in that once formed no part of the glass came in contact with any surface while hot. This is termed ‘fire-polished’. Also a blown glass, a sphere of glass was made, transferred to a punty rod (a solid rod as opposed to the hollow blowing rod) and the open end widened out until by centrifugal force the glass spun to a flat disc. This glass has a lustre unknown on other types, and slight concavity, or appearance of curves, from the method of manufacture.

Plate glass was also used, but was so expensive owing to the many hazards in manually grinding and polishing it, that, as a window glass, use of it was restricted to the very wealthy. Before the 1770s it was blown; the commercial success of the Chance Brothers in casting plate (not an invention since this was previously known) led to cast plate becoming common, especiallyformirrors. Thetime, materials and labour involved ensured that the price did not drop dramatically. The blown disc or cast plate was brought to a mirror-quality surface by grinding with fme sand, then polishing with pumice and rouge. The finished surface does not have quite the same shine as crown. The imperfections are erratic, not running to any pattern.

VARIETIES COMMON

Crown glass: Londpn, Bristol or Dublin crown; noted as carried or sold by side, crate or case. A whole case consisted of 24leaves; half caseswere also sold. Neve’s Purchaser gave various types, the best being Ratcliffs in London of a light sky blue colour. Lambeth glass inclining to a darker green. Hues are attributable to prevalence of iron pyrites, magnesium used to counteract the iron, and general imperfections in raw material. Bristol was considered very desirable in Ireland in the early 18th century, sold, as all crown, in best quality, 2nd best and 3rd best. The first crown glass shop set up in Dublin met with universal esteem, but use of Irish glass was sporadic, the English having had a head start. By the mid 19th century it was losing out to machine-assisted cylinder sheet glass, but was still in wide use; the list of imports into Ireland in 1915 mention crown among items from the USA.

imported in colours in the 18th century, though none of these are listed. It was sold per chest or case, coloured being substantiallymore expensive. It was possibly quite similar to Normandy glass.

Normandy: also a ‘white’ glass, it came in colours, as Burgundy, these not noted. Sold per case, cheaper than Burgundy in the late 18th century. Thornton quotes an early 17th century French source that Normandy was sold in baskets containing 24 circular pieces of blown glass about 70 cm diameter. It was superior to Lorraine glass; Louw notes that in the 1660s it was considered the fmest glass on the English market. Neve’s Purchaser describes it as dirtyish green, more transparent than Newcastle.

Rhenish: no record of use of this glass has been uncovered by me, but details of measures exist. It was sold by the way or webb, containingfrom6oto lOObunches, each of 6 plates about two foot square. The name implies a German source, and Neve notes a German white and green glass - free from spots or blemishes, somefine streaks, like Newcastle. Agreenish tinge to the green glass, both types superior to Newcastle, straighter too.

Newcastle: sold in cribs. This glass was very widely used up till the late 18th century, the commonest white glass to obtain. After the commercial success of crown glass, broad was usually used for quarries, where its obvious imperfections were not so noticeable - the leaded window being less translucent. Neve ascribed to it an ash colour, with specks and blemishes, very often warped.

Muscovy glass is a type which mysteriously has only shown its name in one source so no other information can be given, but it is listed specffically in the window glass section, and for several years, it would be assumed that a mistake was made. Sold by the pound, it was called Muscovy glass or shade. Tantalisingly, at the start of the 18th century, glass listed as imported included that from Norway and the East Country. Any information on this would be gratefully received (and can be passed on by the Editor).

Jealous glass: this seems to have been the first patterned glass, presumably with the purpose of privacy in mind. Neve describes it as wrinkled, cast onamould,

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