Ruby / Corundum:
Resin is a durable and transparent plastic that is especially suited for jewelry-making because of its ease of use. It begins in a liquid form, but after being casted, becomes quite durable. Special resin molds with smooth surfaces are created to give it a glossy finish.
Ruby / Corundum is a crystalline form of aluminum oxide (Al2O3) typically containing traces of iron, titanium, vanadium and chromium. It is one of the naturally transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, ruby if red and padparadscha if pink-orange. All other colors are called sapphire, e.g., "green sapphire" for a green specimen. Because of corundum's hardness (pure corundum is defined to have 9.0 Mohs), it can scratch almost every other mineral.