Pigment Yellow Reactive Black

Microbial discoloration of paints is most often due to reactive metabolism products. A black layer is observed after reaction of the a.m. hydrogen sulfide with traces heavy metals. Yellow to brownish discolorations are frequently observed if thickeners are degraded. Colored pigments are produced by several microorganisms, yellow pigments might be due to Flavobacteria species, red pigments are produced by the yeast Rhodotorula rubescens. 

Saccharides are highly reactive substances that are transformed into many different products, even without the participation of other reaction partners, during food storage and processing. The most common and important reactions of carbohydrates are their reactions with amino compounds that are known as non-enzymatic browning reactions, which also involve reactions of carbohydrates in the absence of amino compounds. Reactions of carbohydrates with amino compounds (proteins, amino acids) are the MaiUard reactions. The products of these reactions are important flavour-active compounds and are yellow, brown or black pigments in many foods and compounds with beneficial properties (e.g. antioxidants), but can also be substances with antinutritional or even toxic effects. 

The use of colorants such as iron oxide was a common practice in the 19 century and natural cement mortars were sometimes tinted red, black, yellow, or brown through the addition of integral pigments. Addition of brick dust to red and brown mortars was also a common practice. While brick dust was commonly used as a pozzolanic admixture for lime mortar, the reactivity of brick dust is low, compared with natural cement, and its effect on hydrauUcity of natural cement-Ume mortars was probably inconsequential. 

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