Top piece (2% perchlorate)
After a fair bit of sublimation. It looks similar to the 5% sample (638), but rinds are again slightly thinner.
Bottom piece (pure ice I)
Can't pick out grain boundaries.
A few regions in 639B had these odd looking areas (lower micrograph). Possible contamination or condensation
LAS email 7/25/2011
As the ice sublimates and you see more and more of the MPH exposed, it gives a somewhat false sense of there being more MPH in the sample (originally) than there actually was.
Similar story with 639A. This composite shows, at the top, a clear overview of the sample surface, again with all ice grains rimmed by MPH. The white outline boxes in the top and middle photos are expanded in the panel below.