We report on the measurement of proton concentration and local viscosity in a polymeric chemically amplified photoresist material. We interrogate these properties using crystal violet, a cationic triphenylmethane dye molecule. To determine the quantity of acid generated by the chemically amplified photoresist material on exposure to UV light, we characterize the pH-dependent linear optical response of crystal violet. To establish a frame of reference for these data, we determine the acid dissociation constants of crystal violet in aqueous solution. The viscosity of the resist material is related to the transient optical response of crystal violet. The data on the photoresist material demonstrate a rapid and persistent pH change in the polymer matrix upon UV irradiation, with the viscosity of the matrix changing by a relatively small amount, going from similar to150 cP prior to processing to similar to190 cP after UV exposure and heating.