Just a suggestion from someone who does this a lot...
You might try using quite a bit more light. The white sheet/cardboard box method does work incredibly well but you'll get much better results if you get some of those clip-on aluminum dish lamps with some daylight fluorescents. Aim for 100W per lamp, and try to use at least 3 (one on top, one on each side). The fluorescents are great because they won't throw nearly as much heat and the daylight spectrum works well with most point-and-shoot auto white balance settings.
Great start though...goodl uck!
