This silvery-white metal superficially resembles aluminum but is extremely heavy. Because it is so malleable, it must be magically altered to the rigidity of steel so it can maintain its shape even when used in combat. This process also catalyzes its magical properties. The following information refers to magically treated platinum.
Armour made from treated platinum grants cold and sonic resistance 2. Platinum armours are one category heavier than normal for purposes of movement and other limitations (for example, whether a barbarian can use his fast movement ability while wearing the armour or not). Light armours are treated as medium, and medium and heavy armoors are treated as heavy. Spell failure chances for armour and shields made from platinum are increased by 10%, the maximum Dexterity bonus is decreased by 2 (which may bring it below 0), and armour check penalties are increased by 3. Armour not primarily of metal is not meaningfully affected. (A suit of chainmail is affected, while a suit of studded leather is not.)
Platinum weapons are considered heavy weapons. Heavy weapons are unwieldy but inflict additional damage. Without the proper Exotic Weapon Proficiency feat (for instance, heavy longsword), you suffer a -4 penalty on attack rolls with a heavy weapon. Only weapons made entirely or largely of metal (such as swords or axes) are affected; other weapons (such as spears) are not.
A character can wield a heavy weapon one size category smaller than his own in two hands to avoid the attack penalty. For instance, a human swinging a light mace made of gold with both hands, or an ogre wielding a platinum longsword with two hands, does not suffer the attack penalty.
You can never use the Weapon Finesse feat with a weapon made of a heavy metal.
Weapons made of a heavy metal inflict increased damage, as shown in the following table:
| Old Damage (Each Die) | New Damage |
|---|---|
| 1 | 1d2 |
| 1d2 | 1d3 |
| 1d3 | 1d4 |
| 1d4 | 1d6 |
| 1d6 | 1d8 |
| 1d8 or 1d10 | 2d6 |
| 1d12 | 2d8 |
Magically treated platinum weighs twice as much as steel, has hardness 10, and has 30 hit points per inch of thickness.
| Type of Platinum Item | Item Cost Modifier |
|---|---|
| Armour | +5,000 gp |
| Weapon damage up to 1d3 | +1,500 gp |
| Weapon damage 1d4 or 1d6 | +2,500 gp |
| Weapon damage 1d8 or higher | +7,000 gp |
Source: Magic of Faerûn (Page 180)