Continuum (a, b) and silicate subtraction (c, d) steps in IRAS 23385 (left) and IRAS 2A (right). The spectrum of IRAS 23385 is binned by a factor of two between 9 and 11 µm due to the saturated silicate profile. A third-order polynomial function is used to trace the continuum, and the silicate profile is a combination of two laboratory silicate spectra (olivine and pyroxene). Panels e and f show the silicate subtracted spectra of both protostars, with major features labelled.