Comparison between timescales relevant for the processing of carbon (left panel) and silicate (right panel) dust grains in an ejecta cloud: cloud destruction time t_dest, cloud evaporation time t_sat, calculated for two temperatures of the gas surrounding the clouds, and dust escape time t_esc, calculated for two grain sizes. Both t_esc and t_dest has been calculated assuming v_gr(0) = v_cloud = 160 km s^-1. All timescales are represented as a function of the diameter of the clump. The vertical line indicates the diameter adopted for the ejecta clouds in Cas A. See text for details.