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. Both took a similar form to that in

Britain. Glassmaking and importation are

covered in the research, which has

thrown up some interesting facts on the

types used and the measures and quanti-

ties which were standard. Glassmakers in

Ireland were almost exclusively foreign,

and importation was far more common

than domestic production, so the infor-

marion listed here will be relevant to

Conservation Officers and others in Brit-

ain who may come up against some of

the obsolete terminology in old docu-

ments and building accounts. A very in-

formative book is that of Richard Neve -

The City and Country Purchaser, 1703.

Each glass type had a different measure-

ment of square footage per case, cribb,

chest, basket, way or webb. Here the

types of glass, with description if known,

are given, and the differing quantities and

measures are listed at the end.

TYPES

Two main types of glass were manufac-

tured 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.

Broad glass is generally termed ‘white’;

a blown cylinder was formed, and when

cooled, a diamond used to cut the 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 man-

ufacture meant that the cutting and laying

out could be done in one operation,

making the whole process much quicker).

The characteristics of this glass are a

pocked surface, with streaks from the

timber battens 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 sur-

face while hot. This is termed ‘fire-pol-

ished’. 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 con-

cavity, 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, especially for mirrors. The time,

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: London, Bristol or Dublin

crown; noted as carried or sold by side,

crate or case. A whole case consisted of

24leaves; half cases were 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 Eng-

lish having had a head start. By the mid

19th century it was losing out to ma-

chine-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.

Burgundy:

a ‘white’ glass, it was also

imported in colours in the 18th century,

though none of these are listed. It was

sold per chest or case, coloured being

substantially more expensive. It was pos-

sibly 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 contain-

ing 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 finest glass

on the English market. Neve’s Purchaser

describes it as dirtyish green, more trans-

parent 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, containing from 60 to l00 bunches,

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,

some fine streaks, like Newcastle. Agreen-

ish 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 imperfec-

tions were not so noticeable - the leaded

window being less translucent. Neve as-

cribed to it an ash colour, with specks

and blemishes, very often warped.

Muscovy glass is a type which mysteri-

ously has only shown its name in one

source so no other information can be

given, but it is listed specifically 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. Tantalis-

ingly, 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 on a mould,

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