We do not recommend variable-contrast filters because they greatly lengthen exposure time. Phenol, also called carbolic acid, emits toxic fumes having a distinctive sweetish odor. Other brands use liquid phenol as a preservative. In our opinion, liquid phenol has absolutely no place in darkrooms because when prints are drying, the buildup of toxic vapor can be hazardous to health. To assure freshness and reliability, the useful shelf life is stamped on the package.
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