OSASTO: KERAMIIKKA- JA LASITAITEEN OSASTO
KOULUTUSOHJELMA: KERAMIIKKA- JA LASITAITEEN KOULUTUSOHJELMA
TEKIJÄ: SIIKAMÄKI RAIJA
TYÖN NIMI: COLOURED GLASS FOR LEAD-FEE BASE GLASSES
In this study the aim was to test the colouring of two different commercial base glasses and the effect of colouring agents to the glass properties.
The study is divided in to following parts, theory, experiments and publications.
The study is based on experimental work. The experiments contained tests of colours given by colouring raw materials (iron, copper, cobalt, chrome, manganese, vanadium and neodymium) in two different base glasses. The colour is measured to spectrum and to three-component values calculated from this. Measuring the colour enables to predict the required concentration of the colorant and thickness of the glass in certain limits. The colour formation of individual colouring raw materials is studied by comparing the measured spectrum to a theoretical spectrum curve.
Additionally, the properties related to colouring agents were studied by testing the relative viscosity and thermal expansion of coloured glass and comparing it to corresponding clear base glass.
Most colouring agents interact with reducing and oxidising agents in the melt. Changes in the melting parameters like the temperature and redox ions present in the glass are studied via copper colouring. The results are reported both as absorption caused by the cupric ion and the colour sensation observed.
An integral part of testing coloured glass was to develop a ceramic crucible. Best properties were found in high-alumina crucible containing kaolinite (40 aluminium oxide (35 %) and feldspar (25 %) plus some additives.
The effect of chemical composition of base glass was clearly seen in visual colours of test samples. The colouring agents not affected by base glass were cobalt and neodymium oxides. In Iittala base glass copper and manganese oxides gave stronger colour intensity than in Philips glass. The colouring agents giving hues of green (vanadium and iron oxides) were more intense in Philips base glass.
In testing relative viscosity the similar patterns were found for both Philips and Iittala glass: iron, copper, manganese, cobalt and vanadium oxides decreased the viscosity of test samples with an increased concentration of colouring agent. Neodymium oxide did not cause a remarkable effect on viscosity.
Results of testing thermal expansion show that with test samples containing more than 1 wt-% cobalt oxide and 1.8. wt-% chrome oxide the difference in thermal expansions exceed the limit of an acceptable seal, when joining to clear base glass.
KEYWORDS: Coloured glass, colour, colour measurement, properties of coloured glass