Transparent glazes can provide passages of high chroma color, alter the hue of underlying paint layers, and soften the transition between different colors.  We have tracked the fading process of the glazes in terms of both their chemical changes as well as their appearance changes.

Our research focuses on:

• Examining the optics of glaze films and the kinetics of the photochemical reactions that destroy the colorant.
• Monitoring the stages of fading and changes in glaze appearance that result from colorant loss during light exposure.
• Determining if the fading behavior of a specific glaze can be applied universally to all glazes.

It was found that the chemical kinetics of fading followed an exponential decay that was dependent on the total light absorbed and not on the film thickness or colorant concentration.  The “fading” of a dark glaze initially produces a shift in hue, which is followed by an increase in chroma.  As colorant is further lost, the glaze proceeds to fade in typical fashion, with chroma decreasing and value increasing.  Glazes having an intermediate reflectance (20-80% over white substrates) suffer the greatest color change for a given dose of light.

 For more information:  
            Bob Feller and Ruth Johnson-Feller pubs.  
            Whitmore et al. JAIC, 36 (1997): 207-230. (Abstract) (pdf [1.2 MB])