"Giselle Flight" Crystal Sculpture, Hadeland Glassverk, 1971

• Lead Crystal - The first clear glass, called cristallo was invented during the 15th century in Venice. Prior to this the glass had a slight yellow or greenish colour as a result of iron ore impurities with the glass. 'Cristallo' was heavily exported .
  
  In 1675, while attempting to counter the Venetian dominance of the glass market, British glassmaker George Ravenscroft invented lead glass, by adding lead oxide to to replace the calcium content in glass.
  
  The new glass he created was quicker to melt, and stayed moulten longer, making it easier to work. More importantly, it had a higher refractive index, adding to its brilliance and beauty, especially when embellished with wheel cut decoration.
  
  Lead crystal, is variety of lead glass, with a higher percentage of lead oxide than lead glass.
  
  Ravenscroft's patent on lead crystal expired in 1681, and more glass makers were able to take advantage of his invention. The expansion in production resulted in England to overtaking Venice as the centre of the glass industry in the eighteenth and nineteenth centuries.
• Faceting - Faceting is a technique of removing material from a curved surface, to give a series of flat surfaces but retaining the profile of the original surface.
  
  The technique is most commonly associated with diamond cutting where the various cuts used such as rose cut and brilliant cut, add life and sparkle to the stone, whilst at the same time removing as little of the stone as possible.
  
  Faceting by grinding is also used to decorate glass. The stems of many drinking glasses are decorated by cutting a series of flat surfaces on a circular stem, and hollow vessels such as vases may have faceted surfaces.
  
  In furniture faceting is often applied to legs of tables and chairs, where a circular baluster shaped section is flattened so as to form an octagonal section.
• Etched - Glass decorated with an etched design, which is achieved through marking out the pattern, protecting the area that is not be etched, and then immersing the object in acid to dissolve the surface of the unprotected area. With some glass objects, such as cameo glass, there may be several layers of different coloured glass, and part of the top layer is dissolved leaving the bottom layer as the background. The longer the time of exposure of the object to acid, the deeper the etching.
  
  The word etching is also sometimes used to describe another method of decoration, where wheel grinders were used decorate the surface, but this technique is usually known as engraving.

This item has been included into following indexes:

• Hadeland Glassworks (Norway) - glass makers 13
• Slang, Gerd Boesen (Norway) - glass makers 2