how to do a good pictures of art pieces:
Photographing Arts, Crafts & Collectibles: Take Great Digital Photos for Portfolios, Documentation, or Selling on the Web (A Lark Photography Book)
It can be anything that's not reflective or wrinkled, like fabric or formica, but most people use special photo backdrop paper. This is really heavy paper that comes in a lot of different colors on a big roll. A good photo store can sell you a chunk off a roll. If you don't wrinkle it, it will last years ( about 25 years).
To get that fade from light in the front to dark in the back, you fasten the paper at the top to a wall, and let it drape in an easy curve down to be flat on the table.
You put the object you're shooting quite a ways out from the backdrop, and set up your lights off to the sides so that the piece is in light, and the background is in shadow.
The light tent is to diffuse the light so that there are no harsh glare spots or shadows. By itself it will not make that graded background. That's purely a function of setup. You can do the graded background thing with or without a light tent.