Category: Construction Materials and Practices

Know Your Glazing

When reading a building facade, our eyes play across the surfaces and our mind analyses what we see in an attempt to identify balance and delight.  Proportional symmetry in fenestration is a crucial part of how our subconscious mind forms an aesthetic judgement and therefore produces an aesthetic emotion.  Although providing ample tutelage on how to balance window openings across a facade, a striking detail often overlooked in eighteenth-century pattern books is fenestration glazing, and glazing furniture.  This is curious when we consider that the thickness of a glazing bar for instance is integral to a facade appearing dense and imposing or weightless and inviting.  It was hardly the case that glazing was not considered of visual importance by the early eighteenth-century architect.  Was its manufacture so controlled as to not necessitate illustrating?  The method of illustrating windows on facades changed over the course of the century, and publications in the latter half of the eighteenth century include glazing bars on their buildings.  By the early nineteenth century the incorporation of fenestration into illustrated facades appears commonplace.

Abraham Swan (A Collection of Designs in Architecture, 1757) includes glazing bars in his designs for interiors but not exteriors.  Matthew Brettingham in his treatise on Holkham Hall (The Plans, Elevations, and Sections of Holkham Hall, 1773) does likewise.  Batty Langley’s The Builder’s Jewel, 1741, exhibits many designs for window architraves and pediments but does not include any sashes or glazing bars.  Colen Campbell’s Vitruvius Britannicus (in 3 vols., 1715, 1717, 1725) does not illustrate glazing bars on external facades, but George Richardson’s New Vitruvius Britannicus (in 2 vols., 1802, 1808) does.

Abraham Swan

Abraham Swan (1757) A Collection of Designs in Architecture, vol.2.

 BrettinghamMatthew Brettingham (1773) The Plans, Elevations, and Sections of Holkham Hall.



Robert and James Adam, New Assembly Room, Glasgow; from George Richardson (1802) New Vitruvius Britannicus, vol. 1.

Hawksmoor, et. al. (The Builders’ Dictionary, 1734) informed by a Mr. Leybourn, note several types of glass available, and report that ‘an English glass-maker went over to France on purpose to learn the French way of making glass; which he having attained to, came over again into England, and set up making of Crown Glass, and in the performance, outstripped the French his teachers’.  The dictionary includes a price for crown glass; between £0.0s.6d and £0.0s.8d per square foot, and a price for ‘looking glass’ at a much higher rate of around £0.4s.0d per square foot.  Interestingly, it also notes a type called ‘Jealous Glass’ costing around £0.0s.18d per square foot, which obscures visibility and is ‘commonly used in and about London, to put into the lower lights of sash-windows …to hinder people who pass by from seeing what is done in the room’.

Steevens Drawing

Steevens Image

The view of the front facade of Dr. Steeven’s Hospital, Dublin as illustrated above (Robert Pool and John Cash, Views of the most remarkable Public Buildings, Monuments and other Edifices in the City of Dublin, 1780) gives an altogether different impression to the photograph.

Early eighteenth-century glazing is composed of a thick glazing bar and a small pane of glass.  Few buildings have retained their early fenestration but included in their number is Dr. Steevens’ Hospital, Dublin (designed by Thomas Burgh, c. 1717) where the heaviness of the glazing bars creates a sense of enclosed fortitude in the facade.  Later in the century this style was replaced by the more delicate composition of light thin glazing bars, which were sometimes made of metal and veneered with timber.


Early eighteenth-century window on basement, Castletown House, Co. Kildare


The windows at Castletown House above basement level were refitted with sashes composed of a thinner glazing bar in the later eighteenth-century.

There were two distinct methods for making glass in the eighteenth century.  The first, crown or spun glass, is made by spinning molten glass into a large disc shape, forming an undulating effect radiating from its centre.  This disc was then cut into panes with the price diminishing as the pane neared the centre of the disc.  The bulls-eye in the centre of the disc was then considered the cheapest of the panes, but is now in fact much sought after as a rare novelty.


An example of Crown glass

The second method, for making cylinder glass or ‘looking glass’, necessitated the forming of a cylindrical shape and then elongating the cylinder by swinging the form into a deep trench.  Whilst molten, this cylinder was cut and flattened out.  This glass is easily identified due to the presence of bubbles in the composition which were circular in the cylinder but became elongated ovals when the cylinder was flattened out.  This type of glass was more expensive than crown glass due to the viewing clarity it afforded the end user.


Cylinder glass with two distinct oval inclusions.

Varying colours clearly evident in eighteenth-century glass is due to the irregular ratios in the composition of materials used in its manufacture, as illustrated in the basement window above.  However, Hawksmoor, et. al. attribute the varying colours to the areas in which they were manufactured; Radcliff glass for instance was a sky blue colour, Lambeth Crown glass a green colour, and German glass either a green or white colour.

It is regrettable that much historic glass has been removed from many historic properties in favour of modern materials whose lifespan comes nowhere close to that of what it replaced.


Posted on 25-05-16

Citation;  McKenna, M. (2016) Know Your Glazing.  Available at (Accessed dd/mm/yyyy)


Leaving Certificate Georgian Architecture Question


Traditional Building Skills Exhibition 2016

Georgian Architecture and the Leaving Certificate

I am delighted to be presenting a paper to Leaving Certificate students at this year’s Traditional Building Skills Exhibition in Portumna Castle, 1.00pm, 7 May 2016.  The lecture will consider the development of architecture through the eighteenth century and will assist students in preparing an answer for the Georgian Architecture question on the Leaving Certificate Art paper.

This lecture and all scheduled lectures are FREE and no advanced booking is required.  You can find more information here, or download the IGS Event Programme.


Castle Grove, Co. Donegal

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Ideally situated below the crest of a drumlin that shelters the house from the northerly elements, Castle Grove is located adjacent to Drongawn Lough, north of Letterkenny, Co. Donegal.  The Grove family were present on the estate since the late seventeenth-century.  It is reported that a house was built in 1695 to replace one burned in a siege in 1690.  The extant facade exhibits the manner of the 1740s though; an adaptation of a townhouse in scheme with plain facade and ornamental doorcase.  The plan too resembles a townhouse layout; a square entrance hall opens onto a staircase to the north flanked on the east by two large reception rooms, and on the west by another.



The main house is three bays wide and two storeys tall.  The tripartite doorcase is of the Doric order in which the free-standing columns work to support the unadorned pediment above, whilst engaged pilasters form ranks on the wall behind.  The sash windows – which are still in working order – are of the mid-late eighteenth-century type, having a thin glazing bar and no joggle or sash-horn.  Much of the glazing has also survived from the eighteenth-century and was made using the cylinder process; a cylinder was formed, elongated, and opened out into a sheet – hence circular bubbles within the material became elongated ovals in the flat sheet.  The windows on the first floor also reveal the interior decoration, having sacrificed the top window pane to the deep coving running around these rooms.



It is apparent that a good deal of redecoration was undertaken in the nineteenth-century.  Externally, over-mantles were added above the ground floor windows and the interiors in the drawing rooms redecorated.  New chimneypieces were installed in these rooms, window shutters and architraves were replaced, and the ceilings were adorned with pre-moulded lime plaster ornamentation.

The ceiling decoration in the front drawing room is composed of a border or repeating panels embellished with abutting floral festoons tied to the ceiling by ribbon.  This is framed within an egg-and-dart, Greek key, and bell flower succession of mouldings to the outside, and a ribboned fascia on the inside.  The centrepiece is an acanthus palmette surrounded by a floral festoon and a bay leaf border.




Given the subject contained within the decoration of the drawing room to the rear, it may have originally functioned as a dining room.  The ceiling frame contains a grape vine presented within the aforementioned series of mouldings.  This Bacchanalian theme is continued in the ceiling centrepiece where the grapevine encircles an acanthus palmette.  The chimneypiece in this room is of the Doric order, with fluted dosseret below the mantelpiece.




Further additions were constructed in more recent times to the north and west of the house.  As the premises is now being used as a hotel, the stables were converted to suit guest accommodation.  The north extension has been finished in good taste and in a manner conforming to the suite of drawing rooms.



It is not clear when the orangery to the west of the front door was constructed; as a structure it may be old, but the large plate glass windows are certainly a modern installation.  The grounds contain a walled garden with the surrounding ‘famine’ wall constructed of local material in order to give work to the locals during that turbulent time.







Posted on 19-04-16

Citation;  McKenna, M. (2015) Castle Grove, Co. Donegal.  Available at (Accessed dd/mm/yyyy)

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