I'm fascinated with the cookbooks written in the 1800's and early 1900's and their use of the word scum rather than foam or floating debris. A good reminder that we have to take time to skim away the things that prevent us from getting the golden goodness like in the end result of slowly simmered broth.
I like to keep my broth making simple. A whole chicken, onion, garlic, and plenty of salt and pepper. Covered in filtered water with an extra few quarts to spare. I simmer on low (covered) for about 24 hours and store in mason jars in the fridge or freezer. If I do not have 24 hours I'll simply raise the temperature to medium or even a boil and reduce the cooking time. A crockpot works just as well. They are perfect for meal replacements or soups.