Opacities for four different materials for a range of size distribution slopes and wavelengths. Values are given for stellar luminosity L = L_⊙, a distance r = 100 au, and a total disc mass M_d = 0.1M_Earth. The maximum object radius is set to s_max = 100 km for water ice and 1 km for carbon and the silicates. Mie results are plotted with solid lines for five size distribution indexes from (top) p = 4.2 to (bottom) p = 2.6. Sloped dashed lines trace power-law fits to wavelengths from λ₁ = 1 mm to the shorter of λ₂ = 7 mm and the maximum wavelength in the tabulated optical data. Vertical dashed lines indicate λ₁ and λ₂.