Spectral regions around the Tc I λ423.82 nm (left column), 426.23 (middle column), and 429.71 lines (right column). The star o1 Ori (black line) is compared to an intrinsic S star (NQ Pup; red line, first row) and to an extrinsic S star (HD 215336; blue line, second row), from HERMES spectra. Third and fourth rows: As in first and second rows, but for 57 Peg compared to the same intrinsic and extrinsic S stars.