At the Smithsonian American Art Museum, you can see a large heart-shaped sculpture made of blown glass. The deep red colored heart is topped with a burning flame also made of glass. It is called the Sacred Heart of Healing and was made by the artist Tim Tate. How did he make this interesting glass form? Today we answer this question as we explore the art of making glass. Throughout history, people from cultures around the world have been making glass. People first found and used glass made by nature. For example, lightning can create tubes of glass when it strikes sand that has the right combination of minerals. Glass pieces produced by lightning are called fulgurites. Obsidian is a kind of black glass formed when the heat of a volcano melts the silica material in sand. Ancient cultures broke off pieces of obsidian to make knives and weapons such as arrows.