  Understanding how disks dissipate is essential to studies of planet
formation. However, identifying exactly how dust and gas dissipates is
complicated due to difficulty in finding objects clearly in the transition of
losing their surrounding material. We use Spitzer IRS spectra to examine 35
photometrically-selected candidate cold disks (disks with large inner dust
holes). The infrared spectra are supplemented with optical spectra to determine
stellar and accretion properties and 1.3mm photometry to measure disk masses.
Based on detailed SED modeling, we identify 15 new cold disks. The remaining 20
objects have IRS spectra that are consistent with disks without holes, disks
that are observed close to edge-on, or stars with background emission. Based on
these results, we determine reliable criteria for identifying disks with inner
holes from Spitzer photometry and examine criteria already in the literature.
Applying these criteria to the c2d surveyed star-forming regions gives a
frequency of such objects of at least 4% and most likely of order 12% of the
YSO population identified by Spitzer.
  We also examine the properties of these new cold disks in combination with
cold disks from the literature. Hole sizes in this sample are generally smaller
than for previously discovered disks and reflect a distribution in better
agreement with exoplanet orbit radii. We find correlations between hole size
and both disk and stellar masses. Silicate features, including crystalline
features, are present in the overwhelming majority of the sample although 10
micron feature strength above the continuum declines for holes with radii
larger than ~7 AU. In contrast, PAHs are only detected in 2 out of 15 sources.
Only a quarter of the cold disk sample shows no signs of accretion, making it
unlikely that photoevaporation is the dominant hole forming process in most
cases.
