Continuation of Figure 3. Full MIRI spectrum of the labeled protostars (black). It shows several absorption features, where the broader one at 9.7 μm is produced by silicate grains. Two blackbody components absorbed by silicates and H₂O are fitted to reproduce the overall continuum. The blue curve represents the fit obtained by considering those spectral ranges that are predominantly absorbed by silicates and H₂O (in red, also indicated by the R1-R4 anchor ranges in top panel). The green curve shows the modeled blackbody emission only absorbed by silicates, while the dotted magenta curve shows the modeled blackbody emission unaffected by absorption. The black dashed curve above the main silicate absorption feature at 9.7 μm is an interpolation of the silicate-absorbed continuum from a polynomial fit. Here, the red vertical line highlights the resulting depth of the feature that determines τ_9.7, whose uncertainty is given by the other two polynomial fits passing above and below (grey curves). The black dashed line at R4 indicates the location of the secondary silicate absorption feature.