Pinakryptol was introduced by Konig and is a family of dyes - the formulary sells yellow, green and white versions. Green is said to be the least effective, can cause staining with some MQ developers but can be used as either a forebath or mixed into the developer. Yellow is more active in reducing panchromatic sensitivity and more compatible with MQ developers but can only be used as a forebath as it is destroyed by sulfite. White is used in the developer. Pinacryptol is probably preferred to older desensitizers like Scarlet N, especially for modern emulsions. Olders desensitizers also tend to stain film.(posted 8275 days ago)With regard to FX2, the story in The Film Developing Cookbook is that Crawley found that PY offered somewhat better discrimination (than conventional restrainers and anti-foggants) between exposed and unexposed grains. Apparently, he also suggested that it should not be used for T grain film. So, it sounds like it has restraining properties in addition to the desensitizing property when used as a forebath.
Cheers, DJ.