If you look for indium on the periodic chart, you will see that it located right by tin (Sn) and lead (Pb) but it is a world away in terms of its properties.
Indium and indium alloys have some unique characteristics that make them ideal for a variety of usages including: soldering to non-metals, low temperature alloys, RoHS compliance, thermal management, battery manufacturing, cryogenic or hermetic sealing and many, many more.
Does your application require you to bond to glass, quartz or ceramic? Then you know that traditional solders will not work. But if you choose Indalloy #4 (pure indium) or Indalloy #1E (52In 48Sn) you will get excellent wetting. If you choose an alloy that includes silver (like Indalloy #290 which is 97In 3Ag or Indalloy #3 which is 90In 10Ag) you will get slightly less wetting but a much stronger solder joint.
Surface preparation along with the proper tools and the proper process are key to acheiving the proper bond. You can get all the details with our PDS, Bonding Non-Metallic Materials Using Indium and High Indium Alloys.