Saturday, 11 February 2017
In history, platinum coins are rare and fairly recent. As far as I know, platinum has only been used for currency in Imperial Russia and colonial South America (areas where platinum is relatively plentiful). Although other coins have been minted in the metal, these have been collector pieces or bullion coins intended for investors rather than everyday use.
This isn't an accident. The main reason one might want to mint in platinum is that the coins are highly durable compared to gold, silver, and copper equivalents. Platinum is hard-wearing and its melting temperature is high enough (1768.3C) to survive an intense wood-fed fire that could melt gold or silver. However, those same qualities pose significant issues for actually minting the coins in the first place. Relatively primitive peoples could and did make jewelry from more easily worked gold-platinum alloys, though not in Europe. (Europeans wouldn't discover platinum until they came to the Americas.) Another big problem for platinum coinage is that it's fairly hard to distinguish from silver. Weight is the best clue because silver weighs only half as much as platinum. Even without scales a person could tell the difference by handling the coins, but for a mixed lot of the type that might be found in a monster's hoard, that's a time-consuming task.
Of course, these aren't nails in the coffin for the existence of platinum pieces. If one buys into D&D as a post-apocalyptic setting, then platinum pieces might be a holdover from the lost ages. It's also worth mentioning that Fireball specifically melts "soft metals such as gold, silver, copper, etc." unless the object saves. Platinum coins wouldn't fall into this class, so fantastic elements would make them more desirable enough for highly magical or technological people in a campaign world to mint them. Dwarves are only the most obvious culprits! In addition, whoever minted the coins might have guaranteed or stipulated their value, in much the same way that modern coinage is given a value higher than the cost of its material by the backing of a nation-state. A fantasy realm powerful enough to guarantee its coinage and advanced enough to work the metal might prize platinum pieces as a hard-wearing currency that doesn't flee to less sophisticated neighbours.
Turning to the practical matters of adventurers, the appearance problem strikes me as an investigation test. To a treasure-seeker peering into a chest by torchlight, platinum pieces wouldn't stand out as anything special. A referee could fairly tell the players, "It's a chest full of silver coins." If no further investigation took place, then the party would be easily swindled by the grasping merchants who keep PC wealth under control - and adventurers who fall into the habit of laying their hands on every silver coin they find become nicely vulnerable to contact poisons! Even adventurers who avoid poisoning and swindles might still have trouble fencing platinum pieces. Such coins are unlikely to be common currency for the reasons given above, so a specialist dealer or collector might have to be found to pay gold for platinum, with various difficulties arising.
Now, I don't raise all of this to scold groups that have used platinum pieces as coin of the realm. The pp has done good work for a great many gamers and it's hardly a "broken" system element in need of a fix. Rather than trying to correct anything, the points above are notes on how platinum could be a more interesting and challenging treasure at my table - and perhaps yours as well.