Soldering to non-metallics is of interest in numerous applications. Bonding to crystal, ceramic or glass is requested commonly. One of the best materials for doing this is indium and only one basic tool is needed in addition to a heat source, indium, and the bonding surface. This is a nickel felt applicator.
Jim Hisert has recently posted a video illustrating just how to do this.
Check it out on Jim's Semiconductor Blog.