Observed polarization wavelength dependence for SN 1986G (Hough et al. 1987), SN 2006X (Patat et al. 2009), SN 2008fp (Cox & Patat 2014), and SN 2014J (this work). For comparison, the data of HD 43384 (this work) and HD 210121 (Larson et al. 1996) are also plotted. The dashed curves trace Serkowski law best fits. For presentation, the curves were normalized to P₀₄ (see text). The error bars were kept at their original values. HD 43384 is a polarized standard; HD 210121 is a Galactic star with very low R_V. For SNe 2006X, 2008fp and 2014J, P(λ) was computed as the polarization component parallel to the polarization angle.