People have been actively buying and selling art for about 250 years. Before then, if you wanted a piece of art, you'd comission it. With the mergence of auction houses in the mid-18th century, art has become something to buy and sell--like real estate, or cars.

When you go to an auction, you are generally seeing works of art that have sold before--whose markets, or prices, have already been set. But what about works of art that have never sold. How does that piece of canvas with paint on it turn into a dollar amount when it gets hung on a gallery wall?

I went to find out along New York's art gallery food chain, first in Williamsburg, Brooklyn.