This was an interesting set up. I had seen a article on doing this but through some bad editing it omitted a vital element. You need two devices to polarize the light. One obviously on the lens but you also need one between the lightbox and the fork. The real background here is white, it is the effect of the two polarizers making it black.
The set up for this is as follows:
I have an old lightbox (for viewing slides actually), that I picked up used, with a 77 mm Hoya polarizer on it. The fork is a cheap plastic disposable utensil. I used a knife and a spoon as well, but I liked the fork the best.
I used my Tamrom 90 mm macro lens with another Hoya polarizer (58mm) on it.
The magic happens as you turn the ring, the background goes black. This is the same way that variable ND filters work: two polarizers "cancel" each other out and block the light.
One recommendation: clean the utensils often. Very often. I ran into the Lightroom problem of slowing down with too much use of the spot removal tool.