Vacuum Leak Plot annotated on Flickr.
The HSL SEM Chamber has several tiny pinhole leaks in the welds. The pinholes were detected by spraying the welds with isopropanol from a spray bottle and watching the response as the alcohol leaked through and then vaporized (and spoiled the vacuum momentarily).
Here I stand, mighty spray bottle in one hand, and determination in the other :) (Photo by Erica Weems)
As you can tell from the plot above, painting the holes with clear nail polish (nitrocellulose laquer) while under vacuum made a nice seal as the liquid was pulled through the leaks and solidified. The DV-6M gauge was brought to 10mV which indicates ~10^-3 Torr.
The next step involves getting cheap surplus valves to seal off the chamber and estimate leak rate in prep for attaching the turbomolecular pump to the system for an ever deeper vacuum. WE NEED TO GO DEEPER!