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Glass objects

This table light holder is from the Medusa Jubilee range manufactured by Rosenthal AG. It was designed by Donatella Versace in 2003. This candle holder is one of a large range of gifts produced as a collaboration between the German ceramic and glass manufacturer Rosenthal and the Italian design house Gianni Versace, beginning in 1993. The design is based on the Greek myth of Medusa, whose hair was made of snakes. The head of Medusa was often depicted on shields to ward of evil spirits. This cinerary urn was found when house foundations were being dug on the French-Italian frontier. The urn was originally clear. Over the years, water and atmospheric pollution have created many thin layers of glass on the outside of this object, which has given it an attractive metallic sheen or iridescence. Accession number 1977.113.11 This Roman glass bottle was originally clear. Over the years, water and atmospheric pollution have created many thin layers of glass on the outside of this object, which has given it an attractive metallic sheen or iridescence. Accession number 1977.113.43 This Roman glass bowl was cast moulded in Alexandria in the early part of the 1st century AD. The bowl was originally clear. Over the years, water and atmospheric pollution have created many thin layers of glass on the outside of this object, which has given it an attractive metallic sheen or iridescence. Accession number 1977.113.03 This Roman glass jar was originally clear. Over the years, water and atmospheric pollution have created many thin layers of glass on the outside of this object, which has given it an attractive metallic sheen or iridescence. Accession number 1977.113.44 This Roman glass beaker was originally clear. Over the years, water and atmospheric pollution have created many thin layers of glass on the outside of this object, which has given it an attractive metallic sheen or iridescence. Accession number 1977.113.41 This Syrian tear-catcher was originally clear. Over the years, water and atmospheric pollution have created many thin layers of glass on the outside of this object, which has given it an attractive metallic sheen or iridescence. Accession number M10380 This Roman glass jar was originally clear. Over the years, water and atmospheric pollution have created many thin layers of glass on the outside of this object, which has given it an attractive metallic sheen or iridescence. Accession number 1977.113.23 This Roman glass jar was originally clear. Over the years, water and atmospheric pollution have created many thin layers of glass on the outside of this object, which has given it an attractive metallic sheen or iridescence. Accession number 1977.113.45

Select each object to find out more about it

Several of the older glass objects in the collection have an attractive metallic sheen or iridescence, but they were not always like that. When they were first made they were clear. Over the years, water and atmospheric pollution have created many thin layers of glass on the outside. As light penetrates the surface and is reflected from each layer it is split into its component colours to give a rainbow effect. Because the colours come from light, and not added pigment, the effect changes as the viewing angle is altered. 

Glass conservation

The recent introduction of new adhesives and synthetic materials has significantly improved glass conservation and repair. Epoxy, polyester and acrylic resins can be made to match colour, shape and even refractive index so that repairs are hardly noticeable.

The new materials must be strong, but not stronger than the glass, so that the glass itself is not broken. They weigh about the same as glass. They have the same refractive index, so that joins do not affect light differently and become obvious. They have the correct viscosity to make a good bond.

The processes must be reversible so that joints can be undone and, since all objects are different, the conservation of every piece has to be worked out individually.

The science of glass

Glass is really a liquid; a super cooled liquid. Its atoms are not arranged in any regular pattern to form crystals and it has no definite melting point, like most other solids. Despite the fact that glass is hard and shatters easily, it flows very slowly, which produces distortions in very old windows. Glass occurs naturally as the result of high temperature events such as volcanoes or meteorite impact.

Sand or quartz (Silicon dioxide) is the largest ingredient (70 - 80%), with around 17% Soda (Sodium bicarbonate) and 7% Lime (Calcium carbonate) in typical glass.

Colours come from various metals added either in an oxygen rich or oxygen-less atmosphere. Iron gives pale green or aqua blue in oxygen rich surroundings or amber in a reducing atmosphere; manganese for purple (oxidising) and clear (reducing); copper for aqua blue to green (oxidising) and opaque red (reducing), copper and cobalt for blue. Antimony in oxidising conditions gives white, whilst antimony and lead together give bright yellow.

Glass timeline

  • Stone Age people used the sharp edges of broken natural glass as tools.
  • Around 3500 BC the first glass objects, beads, were made in Egypt and Mesopotamia.
  • Around 1500 BC pots with decorations were being made in Egypt and Mesopotamia. Phoenician merchants spread glass technology.
  • Between 27 BC and 14 AD glass blowing was developed by Syrian craftsmen.
  • 0 BC - the Romans were using patterned, blow-in moulds.
  • 100 AD - Romans began to make glass windows.
  • In the middles ages Venice became the undoubted European centre of expertise.
  • 1674 - George Ravenscroft, an English glassmaker, patented lead crystal, a brilliant glass for cutting and optical use.
  • 1959 - float glass process invented by Pilkington, St Helens. Large sheets of high quality, very clear glass become readily available at reasonable cost.