Full MIRI spectrum of the G28IRS2 protostar (black). It shows several absorption features, where the broader one at 9.7 μm is produced by silicate grains. Blackbody components (3 in this case) absorbed by silicates and H₂O were fitted to reproduce the overall continuum. The blue curve represents the fit obtained by considering spectral ranges that are predominantly absorbed by silicates and H₂O (in red, also indicated by the R1–R4 ranges). The green curve represents blackbody emission that would only be absorbed by silicates, while the dotted magenta curve shows the modelled blackbody emission unaffected by absorption. The dashed black curve above the main silicate absorption feature at 9.7 μm is an interpolation of the silicate-absorbed continuum from a five-order polynomial fit. Here, the vertical red line highlights the resulting depth of the feature that determines τ_9.7, whose uncertainty is given by another two polynomials (of the order of 1 and 4) fits passing above and below (grey curves). The dashed black line at R4 indicates the location of the secondary silicate absorption feature.