In photography, a means used to strengthen the image of either a negative or a positive; usually, metal is added to the silver image, and the increase in density is proportional to the existing density; thus when a negative is intensified, the highlights are always intensified more than the shadows.

Hydrofluoric acid added to hydrochloric acid for oil well acidizing; the fluoride destroys silica films that are insoluble by hydrochloric acid.