Wavelength-dependent polarisation factors, expressed as a percentage and as defined by Eq. (40), for the particles shown in Fig. 4 for a-Sil/a-C particles (solid lines) and in Fig. 5 for a-C:H/a-C particles (dashed lines) for a_eff = 150 and oblate particle axis ratios of 1.3 (green) and 2 (blue) and prolate particle axis ratios of 1.3 (red) and 2 (violet) for confocal mantles. The long and short dashed grey lines indicate polarisation levels of 25% and 50%.