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Lead Content and Color Variation in Glass Pigments

This presentation explores the relationship between lead content in glass and the resulting color variation when using the same pigment. It discusses the mechanisms of color generation, experimental findings, and preliminary conclusions.

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Lead Content and Color Variation in Glass Pigments

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  1. The same pigment but different colour... WHY? is it due to the lead content of the host glass? Bo Jonson, Glafo ICF, Siena, Nov 11-12, 2001 BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  2. ... if we need a paper!? ... BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  3. Hopefully you don’t need this kind of paper today? BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  4. Background... Previous (lead containing) glass formulations give a specific colour when doped with a pigment / pigment combination. BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  5. but… Introducing the same pigment (combination) in an unleaded formula might give rise to a different colour. Conclusion: The lead content of the host glass controls the colour. Correct? BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  6. Contents - mechanism of colour generation - a selection of performed experiments - preliminary conclusions BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  7. Ionic colouration Mechanism: Colour is due to DE DE depends on: coordination symetry (octahedral, tetrahedral) Intensity of colour depends on the quantum mechanical premises (spin forbidden, spin allowed...) => the number of electrons BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  8. thus... the colour generated from a specific ion is controlled by a) the co-ordination symmetry ...which is due to the glass structure b) the redox state of the pigment ...which is due to the melt oxygen activity, melting and refining / fining conditions a) b) A =e• C • lLamberth-Beers law BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  9. BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  10. Experimental procedure - glass preparation - recording of VIS-spectra, 300-900 mm - attempts to make chemical analysis of various redox states of the pigment BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  11. BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  12. Results... Nickel refined with MoS2 and Sb2O3 Ni with MoS2 Ni with MoS2 (1)Ni with MoS2 (2) Ni with Sb2 O3 BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  13. Nickel in various host glasses octahedral tetrahedral K2O-PbO-SiO2 K2O-CaO-SiO2 host glass Na2O-CaO-SiO2 BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  14. BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

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  18. Conclusions colour variation of nickel is due to the structure / coordination polyhedra potassium glass => octahedral: purple sodium glass => tetrahedral: brownish BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  19. Colour variation of other investigated transition elements is due to the redox distribution. The redox distribution depends on the used refining / fining agent. (Older PbO glasses normally contained As2O3!) BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  20. Reducing power of the fining agents investigated seems to be: (MoS2) > Sb2O3 > As2O3 > CeO2 however, with some exceptions to the effect of MoS2. BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

  21. BJ01\ICF DIFFERENT COLOUR WHY?.PPT 011030

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