However, if the concentration of penetrant contamination in the emulsifier becomes to great, the mixture will not function effectively as a remover. AMS 2644 requires that lipophilic emulsifiers be capable of twenty percent penetrant contamination without a reduction in performance. AMS 2647A requires the emulsifier to be replaced when its cleaning action is less than that of new material. Since lipophilic emulsifiers are oil-based, they have a limited tolerance for water. When the tolerance level is reached, the emulsifier starts to thicken and will eventually form a gel as more water is added.
Hydrophilic emulsifiers have less tolerance for penetrant contamination.
The penetrant tolerance varies with emulsifier concentration and the type of contaminating penetrant. In some cases, as little as one percent by volume of penetrant contamination can seriously affect the performance of an emulsifier. The percentage of added penetrant required to destroy washability of the emulsifier can be measured and an oil tolerance index is commonly used to compare the tolerance of different emulsifiers to contamination by penetrants. AMS 2647A requires that the emulsification bath be discarded if penetrant is noted floating on the surface or adhering to the sides of the tank. Water contamination is not a concern with hydrophilic emulsifiers as they are miscible with water.