Attrition on drying: vitrification on grinding
Subject to dryer design, crystals can be eroded during drying operations and become rounded as a consequence. Accordingly, a tablet would take a cushion or rounded almond form with a rough surface from a microscopic perspective.
Sugar crystals are susceptible to vitrification when finely ground, but their surface will be smooth.
Crystals only present concavities if there are dendrites or macles (interpenetration of two crystals) present or at the beginning of dissolution.
The color of a crystal is due to:
- - the presence of specific radicals in the molecules;
- - the disposition and nature of metallic ions that it contains (chrome yellow, cobalt blue, iron oxides beige and brown, titanium white and, though not a metal, carbon black).
Recall that the pigments (such as those mentioned above), like a great majority of minerals, are insoluble in water, unlike colorants that are organic molecules and soluble in water (chlorophyll, hemoglobin, to cite only two colorants). Certain colorants are used, together with pigments, in plastic materials, but they are expensive.
A measurement of sugar coloration is obtained by the absorption of light with a wavelength of 420 nm.