The manufacture of optical glass

Abstract

The history of the manufacture of Optical Glass can be divided into four epochs, Guinand's discovery of the stirring process in 1796, the work of Abbe and Schott circa 1882, and the development in England during the Great War being the outstanding features in this history. The method of manufacture is practically the same at the present time as in Guinand's day, any improvement being one of degree rather than of kind. Thus the glass is melted in special pots and furnaces, stirred after founding, and allowed to cool in situ. When cold it is broken up and examined. Defective glass is rejected, and the good glass is moulded into slabs, prisms or lenses, and finally annealed. Optical glass has to conform to a rigorous specification. It must have certain specified optical constants, must be free from striae, bubble, strain, and colour, and must be durable. The manufacture of optical glass is based upon continuous research into the properties of glass. The effects of composition upon density, refractive index, melting properties, durability, freedom from colour, and devitrification tendencies, have to be studied upon a small scale, and the results translated into terms suitable for works practice. The whole manufacture indeed is research upon a manufacturing scale.