In Old School RuneScape, metals are elements that are malleable, hard, and conduct magic in most cases (though metals such as elemental metal do not follow this rule). They are typically found in the weapons, armour, and equipment players use, but also in monsters as well.
These metals are used by players in the Crafting skill.
Black metal is stronger than steel, but weaker than mithril. It is also equal in power to white and is available to free-to-play players. Black, like dragon and white, cannot be smithed. This makes it more valuable, sometimes more than mithril or even adamant weapons and armour. Black weapons and armour can only be obtained by being bought from stores or other players, picked up from monster drops or respawn points, or (as a member) received from Treasure Trails. As its name suggests, it is black in appearance. Black metal armour and weapons are used by the Black Knights.
White metal is used by the white knights. White metal, along with black metal, is made by different forging techniques which slightly increases the defensive capability.
Dragon items are members-only and often require completion of a quest to be usable. Dragon metal items are a distinctive dark red in colour, and their shapes differ from similar items of different metals. Dragon metal weapons all have a special attack. Dragon items are generally sold at high prices in shops or dropped by high-levelled monsters.
Note that dragon arrows and darts are not made from dragon metal at all; they are simply fletched from the talons of a dragon. Some weapons or armour are not currently existent in the form of Dragon - for example, there are no dragon throwing knives.
As the name implies, silvthrill is an alloy of silver and mithril in a 1:1 ratio. It is potent against vampyres and therefore plays a role in the Myreque quest series.
Elemental metal can only be obtained during and after the Elemental Workshop I quest. It is purple in colour. At Smithing level 20, elemental ore along with four coal can be smelted into an elemental metal using the blast furnace in the Elemental workshop. This bar is used to smith the elemental shield during and after Elemental Workshop I and the elemental helmet after Elemental Workshop II.