Just beecause yer feedstock stash is white and looks clean is no gaurantee that gaaks are not present.
Unfortunately...most never know it until the post-rxn final work-up such as what was already encountered in the last batch!
Truer words were never spoken.
The appearance of the feedstock and clean and white means nothing. The nastiest of the gakks can hide in the clean white feedstock and you won't see them until the post reaction workup when its too late. Visual clues to the cleanliness of the feedstock can be the most deceptive.