To be safer, use a double boiler arrangement. Don't go gourmet on this, tho'. Just put a small can in a frying pan with a couple of inches of water. Then put your fat inside the smaller can. The idea of a double boiler it to keep direct heat from your fat, so it does not burn or IGNITE! The inch or two of water in a frying pan, boiling, will transfer enough heat to reduce the chunks of fat to oil, and if you do this in small enough quantities, you don't have to worry so much about handing a can full of Hot Oil. Take your time.
When I boiled down fat we used a huge iron pot over an open fire. It had probably 8 gallons of water in it, or more, and we just threw large chunks of fat into it. As the oil came out, we skimmed it off with a large ladle and poured it into a smaller jar or can to cool. That gave us congealed oil with all kinds of stuff in it, most settled to the bottom. When we had enough, we heated that mess up again, and then poured it through filters and strainers to get rid of the debris. The filtered oil would come out pretty pure, and look only a light yellow in color, not much different that the oils we now buy in bottles. However, depending on what fat you are rendering, you get different flavor and taste. Some of this when cooled will congeal like Crisco. Others, like bear fat will give you a nice jar of oil. I used to know the reason for that, but I have forgotten. I am sure someone will remind me.
