I'm not sure that a light box will solve all the problems. You also need some light sources from above to add sparkle to your pieces. Add some highlights. I bought some cheap photo reflectors w/ clamps attached at my local Lowe's/Home Depot. Then I used daylight or full spectrum light bulbs to keep the colors true.
OK, now I'm gonna give you some advice as a photographer & AV person. Please don't be offended. Using the flower makes a nice "glamour" shot & catches attention, but it distracts the eye away from the main event -- your necklace. I like the subtle scrapbook paper for background detail, but the flower is kind of overpowering your piece b/c it's so much bigger than the scale of the necklace. My advice is to stay w/ your main focus [your jewelry] & leave the magazine shots to the pros. Believe me, they have lots of tricks that you'll never get around to nor do you need to. Even if you're taking pix for a juried show, they really want to see your work & your craftsmanship up close.
Soooo, I hope this is taken in the spirit it was intended -- to be helpful, not critical. And good luck w/ your photo set up.
sher