Molten glass is used in the Crafting and Construction skills. Fritz the Glassblower on Entrana will teach you how to make molten glass. Molten glass can be created through the Crafting skill by using a bucket of sand with soda ash on a furnace, granting 20 Crafting experience. Strange rocks for Crafting may occasionally be found while making molten glass.
Alternatively, you can use the Lunar spell Superglass Make, which converts all buckets of sand and all seaweed or soda ash into 30% more molten glass. This method does grant experience but only gives 10 experience as opposed to 20 from using the furnace.
Turning molten glass into Empty light orb, then disassembling them is a solid way to gather Enhancing components for Ironman Mode accounts.