D892 Foam Test — Ceramic or Metal Diffuser?
Although the method allows both a circular, Norton ceramic (stone) diffuser and a Mott cylindrical metal diffuser, there are advantages and disadvantages to each. The stone diffuser was used for many years before the introduction of the metal diffuser. Both need to meet certification requirements but the metal diffuser is much more uniform, easier to clean, and holds it specification for a much longer time than the stone diffuser. Based purely on the geometrical design, the circular stone diffuser produces larger bubbles, since the bubbles, as they are produced cling to the side of the stone and move upward. They then coalesce at the top of the stone thus forming larger bubbles. The larger bubbles cause the foam to break more easily, thus giving slightly better foam results.
Lawler makes several models of foam testing apparatus and diffuser certification apparatus.