Series editors' preface - Wood Tools

216 Conservation of Furniture
(a) (b) (c)
Figure 5.17 Stages in the production of crown glass. (Illustrations from Dionysius Lardner (1832) ‘A treatise on
The Progressive Improvement & Present State of the Manufacture of Porcelain and Glass’: part of The Cabinet
Cyclopedia, Useful Arts Series, Longman, Rees, Orme, Brown & Green, London)
work. Some broad glass was ground and
polished to produce distortion-free glass for
common mirrors.
Crown glass was probably produced as
early as broad glass and the two methods
were both used off and on during subsequent
centuries. As with broad glass, the first stage
is the blowing of a globe but in the crown
method a solid ‘pontil’ rod is then attached
opposite the blow pipe which is then cracked
off leaving a round hole. The globe is spun
on the pontil in front of a hot furnace opening
until the hole enlarges. As the heat increased
the globe eventually ‘flashes’ or opens out
suddenly into a slightly convex flat crown. The
disk is cooled in the air sufficiently that it will
not be imprinted with anything when it is laid
down and the pontil iron is removed (Figure
5.17). The resulting glass was the best quality
that could be produced by hand methods
because of its thinness and regularity and
because it had a fire polished surface on both
sides. Semicircular thickenings and lines of
bubbles can often be seen in crown glass
(Figure 5.18). The centres of the sheets
bearing the pontil scars (bullseyes) were used
in glazing the cheapest windows.
Figure 5.18 A window pane made from crown glass
showing characteristic curved striations, in the window
of a late seventeenth-century period room, Yale