Glass

Manufactured glass is often a byproduct from various manufacturing processes. Slag glass is a result of smelting metals, particularly iron. Iron ore is heated to high temperatures, which melts the metal. The iron is in rocks that contain other minerals and during the melting process, silica rises to the surface, where it is skimmed. When it cools, it forms glass. Slag glass can be differentiated from natural glass like obsidian because it typically has a lot of air bubbles in it. Melted silica that is cooled into glass is made through other manufacturing processes and sometimes is even made intentionally for its patterns and ease of use in forming into products.