Cracking is the splitting of a bar along the side seams or at any part in the bar during use. Cracking of a soap bar in use conditions is a perceived as a negative by consumers.
Cracking is evaluated by partially submerging bars in water of fixed hardness and temperature for a set period of time. The bars are then dried and evaluated for cracking after one to two days. Ideally, there should be no cracks present in the soap bars.
Bar hardness is a mechanical measure of how resistant the bar is to physical pressure. Bar hardness can be mechanically measured in finishing trials for machineability as well as during routine lab evaluations. Bars that are too soft may be difficult to extrude on the finishing line without significant surface defects.
Bar soaps are typically evaluated for dry specks and drag. Specks of dry soap (insoluble soap) can occur during the manufacture of the base soap or syndet or from the additives in the soap bar. These specks show up as distinct bumps on the surface of the bar. The bar is washed under controlled water conditions with cooler water bringing out more obvious dry specks. The bar is both evaluated during wash and after drying for feel and appearance and rated against standard quality bars.
Clearly, next to the fragrance preference at the point of purchase, skin feel and lather are the most important attributes for consumers. Various skin feel attributes from bar soaps are evaluated by a trained panel of experts. These groups of panelists are trained to evaluate small (or large) differences in products focusing on a set of defined attributes. Products are usually compared with a reference product. Examples of attributes evaluated by a trained panel for skin feel include time to rinse, skin slip, tightness of skin after drying, and smoothness of skin.
Clinical Evaluations of soap products are used to determine how effective the products are on certain attributes, primarily mildness/irritation, skin dryness/tightness, antibacterial efficacy, and deodorancy. There are several methods of measuring the clinical attributes of a soap bar ranging from trained panels to biophysical instrumentation [1,2,23].
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