Tianmu teacups originated from Song Dynasty, located in Jianyang Kiln which was near the Tianmu mountain, the junction of Fujian and Zhejiang . The so-called oil droplets means that there are oil droplets in different shapes and sizes , look like floating on the water , in the colors of silver-gray or iron-brown with metallic luster dotted in the black glaze. It is so named of this. It was also called "Star light” in Song Dynasty due to it is like the shining stars at night. Firing the glaze, the formation of oil droplets is due to the period time of the firing, the oxide of the iron accumulation in the growing bubbles, at the high temperature above 1200 degrees celcius. When the bubbles grow to a certain extent, crystallize out from the form of hematite and magnetite and formed the shape like the crater. Then it become flat again, and turns to oil droplet-shaped crystals. This glaze, as high iron content, will produce magnetization at high temperature, resulting in trace minerals. It makes the water in the teacup softened and eliminates the astringent, so the water turns into sweeter and milder. It will also make it smoother and tastier if use it for hard drinks.