Glass and Ceramics 161
invention, and glass, which followed later, are important indicators of the
technological development of mankind. Improvements of their basic but
sophisticated manufacturing techniques have defined milestones in the his-
tory of technology. Moreover, both materials reflect the creative potential and
the artistic expression of craftsmen throughout our history. Apart from
objects of daily use, decorative art and architectural elements have also been
produced during the centuries and testify to the needs and achievements of a
specific culture. Thus glass and ceramics have common links in chemistry
and in history and they are often considered together, not only in the field of
conservation but also in science and technology.
2 Deterioration and Conservation of Glass
2.1 History of Glassmaking
Before dealing with man-made glasses, their natural analogues should be men-
tioned. Glasses occur in nature as a result of the rapid cooling of silicate melts
(magmas) as they come into contact with water, ice or the atmosphere. Silicate
melts may originate from magmatic activity or from meteoritic impact and
exhibit a broad range of chemical composition (from 30 to 80 mass% SiO 2 ,
up to 20 mass% MgO and CaO). Obsidian, as one of the most popular repre-
sentatives of natural glasses, has been used by man as an extraordinarily
effective sharp-edged tool from the earliest times of our archaeological
record.
The cradle of glassmaking is difficult to define, both concerning the date
and the place of birth of this new invention. Northern Mesopotamia at a time
prior to 2500 BC is an estimation shared by many experts. At first, decorative
objects and glass beads had been hand-formed or cast using simple tools and
finished by abrading. Later on, glass was moulded or pressed to form vessels.
Figure 2A ceramic storage vessel from the 17th century, German origin
(Picture provided by Staatliche Akademie der Bildenden Kuenste Stuttgart, Germany.)