Upper: the effect of increasing the maximum grain size on the the τ_9.7 versus E(J − K) relationship. The minimum and maximum grains size are given in μms. lower: the effect of increasing the maximum grain size on the shape of the 9.7 μm silicate feature. The left panel shows the calculated 9.7 μm silicate absorption profiles in terms of the mass extinction coefficient and the right panel shows the same profiles normalised to 1 at 10.5 μm as was done with the observations. The solid line in both panels represent the best fit for the Galactic centre feature from Min et al. (2007).