Slit-island analysis (SIA) has been successfully used to measure the fractal dimensional increment (D*) of fracture surfaces. The fracture toughness in brittle ceramics is related to the fractal dimension. However, the measurement technique may affect the determined D* values. The purpose of this study was to determine the contour angle at which a valid fractal dimension measurement could be obtained using the SIA method for baria silicate glass-ceramic and zinc selenide ceramic. Two specimens of each material were duplicated for each of the following contour angles: 0 degrees, 3 degrees, 5 degrees, 7 degrees, 22 degrees, and 90 degrees. After polishing to 1 mum alumina slurry, the coastlines were photographed and arranged in a collage. The coastline was analyzed using the Richardson technique. Results showed that the SIA technique is sensitive to the contour angle since D* decreases with increasing contour angle for both materials.