When I am making broth, I put a bunch of bones and water in an 8- to 16-qt pot with a few tbsp. of apple cider vinegar, and simmer it overnight. I skim the scum off the top, and try to use as many cartiligenous ingredients as possible (duck or chicken feet, knuckle bones, etc.). Good broth gells when it cools, but it's still nutritious if it doesn't gell.
Recipe section