Mixed media: When several media are used for the same currency, this provides of course maximum flexibility. The historical evolution of conventional money has traced a logical sequence towards more convenience: one started with physical commodity money (such as precious metal coins used to be); but now it is more convenient to handle paper receipts with promises to pay that physical commodity (“I will pay to the bearer the sum of one Pound Sterling” is still written on the English currency bills). And of course, if the appropriate technological infrastructure is available electronic bits are even cheaper to move around than paper currency. The same currency can and often does take different forms depending on the media that supports it. For instance, national currency takes many forms: electronic bits, paper, or coins.

The advantages and disadvantages of each of these media are relatively straightforward.

Commodity currencies have as advantage that one doesn’t need a lot of social or legal infrastructure to make them work – it is the only currency that can operate in extreme circumstances such as civil war, social or economic chaos. Such “currency” can be literally consumed directly by the recipient as a last resort, and it is also most impervious to counterfeiting. Its inconvenience is also clear: limited flexibility to create it; and it can be inconvenient to store, handle and transport as well.

Paper currencies in contrast are among the easiest to handle, and are cheap to produce. But they have as downside that they can also more easily be counterfeited. With today’s high quality photocopying equipment available to almost anybody, security is a perpetual issue for paper currencies. Even for complementary currencies, this issue needs to be addressed as soon at they become successful enough to make it worthwhile for someone to counterfeit them.

Electronic media are fairly familiar by now. PCs are the most common support for small to medium-sized complementary currency systems, and are satisfactory if one has access to phones and other communication means to convey the information to the person handling the PC. Their downside is that such an approach tends to require a labor intensive way to process the transactions.

Internet connections in which the users update their own transactions reduce the cost of overhead, but create additional risks for fraud, and not everybody has an easy access to a computer. Smartcards combine the advantages of both, but require readers that are both expensive and not commonly found anywhere but Europe and Japan at this point. The best electronic solution would be to have the complementary currency piggy-back on another smartcard application, such as a public transport or a bank-smartcard. That way the marginal cost of adding the complementary currency application becomes very reasonable.

Mixed media is of course the ideal, because one can tailor the advantages of each form to whatever the specific application of the currency. But as a downside one should remember that particularly from a security viewpoint, whatever the weakest media is ends up also as the weakest link of the entire chain.