Macromolecular oxidation was detected in proteins by the colorimetric measurement of Advanced Oxidation Protein Products (AOPP) and in lipids by the colorimetric quantification of malondialdehyde (MDA). Standard curves were run with chloramine-T and 1,1,3,3 tetraethoxypropane (TEP) for AOPP and MDA methods, respectively [29], [30], [31]. Values were normalized to initial protein content in samples, measured with Bradford reagent [32]. The standard deviation of at least six measures was calculated and p-value < 0.05 were considered significant.

Although barium sulfate is almost completely inert, zinc sulfide degrades upon exposure to UV light, leading to darkening of the pigment. The severity of this UV reaction is dependent on a combination of two factors; how much zinc sulfide makes up the pigments formulation, and its total accumulated UV exposure. Depending on these factors the pigment itself can vary in shade over time, ranging from pure white all the way to grey or even black. To suppress this effect, a dopant may be used, such as a small amount of cobalt salts, which would be added to the formulation. This process creates cobalt-doped zinc sulfide. The cobalt salts help to stabilize zinc sulfide so it will not have as severe a reaction to UV exposure.