Measurements have been made of the glass transition temperature and the viscoelastic parameters of prepared paint samples and complex samples from paintings at increasing values of relative humidity in the range 54-94%. The complex modulus data obtained from dynamic mechanical measurements were fitted to the Williams Landel Ferry equation. The real part of the complex modulus was found to fit the equation, and time temperature superposition was used to make predictions on the long term effects on the storage modulus of samples exposed to these conditions. The lack of fit of the loss data, however, made it necessary to consider an alternative model which takes into account several relaxation processes. Dielectric measurements on these samples showed that the resulting complex permittivity data could be fitted using a cooperative model given by the Dissado-Hill function. Values of the parameters calculated by this function are given for the corresponding values of relative humidity.