Mercury dissolves many metals such as gold and silver to form amalgams. Other metals that do not form amalgams with mercury include tantalum, tungsten and platinum. Caesium forms alloys with the other alkali metals, gold, and mercury (amalgams). Unlike many other metals, iron does not form amalgams with mercury. Lewin informed him also about mercury exposure from dental amalgams. Other elements that do not readily form amalgams with mercury include platinum. The ancient Romans often used mercury-tin amalgams for gilding their armor. The reduced mercury which results forms amalgams with cartridge brass, weakening it, as well. Relative ratios between the other metals used in dental amalgams has also been highly variable. For example, such amalgams are known with gold, zinc, sodium, and many other metals. Examples of alloys are steel, solder, brass, pewter, duralumin, bronze and amalgams. Common resin cements utilised for bonded amalgams are "RMGIC" and "dual-cure resin based composite". It is still used as an ingredient in dental amalgams. Sodium amalgams can be purchased from chemical supply houses. The vast majority of past studies have concluded that amalgams are safe.