Spectral and polarization properties of the Mg I b₂ line. Top: Reference continuum intensity in Fe (at +532 mÅ) normalized to its mean QS value I₊₅₃₂/I_QS+532, continuum intensity in Mg (at −700 mÅ from the line core) normalized to its mean QS value I₋₇₀₀/I_QS−700, and maps of TLP and TCP. Bottom: EW, LD, δAr, and δAm. The regions with Stokes V signals smaller than 5σ have been masked in the maps of the Stokes V asymmetries. Dashed contours are placed at I₋₇₀₀ = 0.5I_QS−700 of the Mg line to highlight the pore locations, and the orange arrow in the first panel points toward the disc center.