The importance of maintaining the correct pH in the soaking operation cannot be overstated. The influence upon accelerated soaking systems, as well as on the activity of enzymatic soaking assistants, makes this a most important control parameter.
It has become the general practice to soak with soda ash, caustic soda or magnesium oxide at pH levels around 9.5 - 10.5. The reason for this is that bacterial growth is substantially less at this pH and the skin fibres more readily absorb water at this alkalinity. Enzyme soaking agents such as PELLVIT are optimised at this pH. In addition, when such alkalis as soda ash or caustic soda are used to achieve alkalinity this also has a scouring effect or partial saponification on fatty substances, this is particularly effective in combination with emulsifiers.
Sodium sulfide may also be used both to achieve a mild degree of alkalinity and to pre-treat the hair and epidermis with reducing agent during the soak.