  We present a first detailed spectrum synthesis calculation of a
supernova-fallback disk composed of iron. We assume a geometrically thin disk
with a radial structure described by the classical alpha-disk model. The disk
is represented by concentric rings radiating as plane-parallel slabs. The
vertical structure and emission spectrum of each ring is computed in a fully
self-consistent manner by solving the structure equations simultaneously with
the radiation transfer equations under non-LTE conditions. We describe the
properties of a specific disk model and discuss various effects on the emergent
UV/optical spectrum.
  We find that strong iron-line blanketing causes broad absorption features
over the whole spectral range. Limb darkening changes the spectral distribution
up to a factor of four depending on the inclination angle. Consequently, such
differences also occur between a blackbody spectrum and our model. The overall
spectral shape is independent of the exact chemical composition as long as iron
is the dominant species. A pure iron composition cannot be distinguished from
silicon-burning ash. Non-LTE effects are small and restricted to few spectral
features.
