The history of glass dates back to 4000 BC, when early humans used natural obsidian to tip spears and man-made glass to coat stone beads. In the 1st century BC, glass blowing became common for making containers, which were colored due to impurities in materials. During the Roman Empire, glass-making skills spread across Europe but were closely guarded until the Empire's fall in 476 AD. Modern glass manufacturing techniques developed from the late 19th century onward through advances in technology. Today glass is widely used and recycled, and the industry produces millions of containers globally each day.