Chinese Coin With Strange Back Ground

"Strange backgrounds" on cash coins like this are a surefire sign that what you are looking at is actually a machine-struck replica of a cash coin, and not an authentically cast object. The mottling is supposed to simulate the rough, sandy backgrounds found on genuinely cast pieces.

Given that the pattern repeats - you can see the same shapes both to the left and to the right of the top character, for instance - I'd say the pattern was rolled onto the die print-fashion and then acid-etched into the die to create the 3-D effect.