While this particular scam is usually referred to black dollar scam, actually any worldwide currency can be used for the act. The victim somehow has been involved into believing they can get rich quick through actual money laundering. Victims are conned to believe they literally can wash money. The con artists can be very charismatic, intelligent and persuasive individuals who search for foreign victims with a promise they can get rich quick. Don't underestimate the skills of these scammers!
Unsuspecting, the victims are being presented with a suitcase full of black paper in the size of real money. Scammers will tell this money is painted black to get past the airport scanners or being refused by the government and as such now painted black. Mixed in this suitcase are a few real bank notes, which are painted with a black substance. The suitcase is shown to the victim. The criminal, appearing as if choosing the black dollar randomly, while knowing exactly where he hid the few real painter black notes, picks the bank note and pours it into a "secret chemical substance" and thus making the black paint go away from the real money.
The victim then is being told that this whole suitcase can be washed with this "expensive substance". A huge potential return on investment and greed opens the wallets of the victims, who pay large sums, usually tens of thousands of dollars for this supposed secret chemical liquid. After the substance has been bought by the victim, the criminal will give instructions for the use of the chemical remover and all of these instructions will be made to buy scammer a little time. Either that you are supposed to place the substance into a refrigerator for 96 hours... or after you have mixed all the ingredients, they have to stand still a particular amount of time. Of course after you realized you are washing black paper with water and an aspirine in it, it is already too late.
Source : http://www.bustathief.com/2007/08/black-dollar-black-money-scam.html