The best way to achieve a great marble is by alternating scoops of the different coloured batters side by side and on top of each other. When the batter is all gone, take a chopstick or the end of a knife and draw a squiggle down the loaf in multiple "S" shapes. After, take the chopstick and make and "S" shape in the opposite direction. Make sure that you only do this a max of 5 swirls or the loaf will be blended instead of swirled.