These agents include optical brighteners, fabric softeners, and colourants. Laundry detergents contain a mix of ingredients including surfactants, builders, optical brighteners, etc. Benzoxazole derivatives are also of interest for optical brighteners in laundry detergents. Methylketol is used as an intermediate for synthesizing dyes, pigments, optical brighteners, and pharmaceuticals. Ions, catalysts, brighteners and accelerators can be measured. Optical brighteners have replaced bluing which was formerly used to produce the same effect. The production of stone paper uses no water, acid, bleach or optical brighteners. Some non-stilbene brighteners are used in more permanent applications such as whitening synthetic fiber. Optical brighteners have also found use in cosmetics. All brighteners have extended conjugation and/or aromaticity, allowing for electron movement. Brighteners can also be "quenched". Brighteners are commonly added to laundry detergents to make the clothes appear cleaner.