The Bidirectional Texture Function (BTF) is a very realistic material representation, but it does not offer the user good control and editability over the data. Users can not change the BTF data in a simple and effective way. We present a method for simulating the painted appearance of a material that is represented by the Bidirectional Texture Function. We first transform the image-based BTF into a simple representation that is composed of a height-field and a spatially varying bidirectional reflectance distribution function (SVBRDF). This representation allows us to simulate the appearance of paint on the surface and to estimate the reflectance of the material after being painted. During rendering, we combine a currently existing BTF rendering technique and the modified material data to simulate the painted appearance of the BTF material. Our experiments show that the proposed approach can change the material appearance while preserving the impressions and feelings of the original BTF.