  Although the colour distribution of globular clusters in massive galaxies is
well known to be bimodal, the spectroscopic metallicity distribution has been
measured in only a few galaxies. After redefining the calcium triplet
index-metallicity relation, we use our relation to derive the metallicity of
903 globular clusters in 11 early-type galaxies. This is the largest sample of
spectroscopic globular cluster metallicities yet assembled. We compare these
metallicities with those derived from Lick indices finding good agreement. In 6
of the 8 galaxies with sufficient numbers of high quality spectra we find
bimodality in the spectroscopic metallicity distribution. Our results imply
that most massive early-type galaxies have bimodal metallicity, as well as
colour, distributions. This bimodality suggests that most massive galaxies
early-type galaxies experienced two periods of star formation.
