Examples of the IBIS Fe I 617.3 nm line data analysed in our study; letters (numbers) between brackets indicate the line (column) label. a) Stokes I in the continuum near the line, b) Stokes I in the line core, c) Stokes V in the blue wing, near the line core, at four stages of pore evolution, from data taken at (1) 13:58 UT, (2) 16:09 UT, (3) 19:45 UT, and (4) 20:35 UT. North (west) is at the top (right). The black box in the top panels shows the subfield inverted with the SIR code and shown in Figs. 5 and 6. The contours overplotted in each panel indicate the location of the evolving structure, as singled out by applying an intensity threshold criterion, I_c< 0.9I_qs, where I_qs is the average quiet Sun intensity. More details are provided in Sect. 3.1.