Mother of pearl is formed in the depths of the sea and harbours very unique features such as iridescence and opalescence. No two specimens are alike, which gives the watch a unique character, especially for ladies watches, both on the dial and on other elements. A sapphire crystal gives a watch the following properties: extremely high resistance to impact and superior screen and hand readability thanks to its transparency. Because it is the strongest material after diamonds, it is used in fine timepieces for its anti-scratch prowess. Sapphire crystals can take many forms and give the watch a variety of looks: flat, domed, concave or ground. All Tissot watch cases undergo several tests, including a water resistance check. Tissot tests the watch's ability to resist impacts and pressure, as well as the penetration of liquids, gas and dust by replicating the real-life conditions in which the watch may find itself.