Investigation Of The Relation Between Composition, Colour And Melting Atmosphere In Ancient Glasses(Forest Glasses) By Electron Spectroscopy And Electron Spin Resonance (Esr)

Forest glasses of the 16th and 17th centuries have been investigated spectroscopically (uv, visible, and near infrared) and by electron spin resonance to seek a relation between the observed colours and the then existing melting techniques. By using model glasses it has been shown that the very wide range of colours found in old glasses can be obtained from only two elements; iron and manganese,which are found in the raw materials, if the oxygen partial pressure is varied during melting. Both of the experimental methods provide information about one side of the iron manganese redox system. From the data on old glasses it can be concluded that oxygen partial pressures of 10-4 to 10-7 bar were achieved in melting.