Materials you'll need are:
1. Big, strong magnet (or several small ones. I used my modified 6x8 speaker magnet)
2. Little, strong magnet (I used one of my magnetic darts)
3. Hoe (optional)
4. Plastic sandwich bags
5. Mortar and pestle
6. Small container and a lid
7. Large container
Step 1: Finding a good fishing hole....and cast out.
One of the best areas to find a good source of ferrous metals is the ground....No seriously, where do you think metal comes from? Don't answer that...
A mixture of gravel and sand is usually one of the better spots for this (beaches are also great, but I'm not there).
1. Use the hoe to break up the surface of the ground into a small pile of dirt.
2. Put your large magnet into one of the sandwich bags and hold onto it with your hand. Keep the large container close by.
3. Now start to sweep the ground as shown in the last picture. You can push the pile of dirt out, to get at the metals underneath. Move your hand with the magnet around as if you were washing the ground....
Step 2: Reel 'er in....Grind 'er up.
1. When you look at the bottom of your magnet, you should see pebbles, sand, and slivers of metal sticking to the bottom side. Now put your magnet over the large container and peel the bag away from the magnet, starting from the top (Just to clarify things....keep the magnet inside the bag and use your other hand to seperate the side of the bag with metal on it away from the magnet so that the metal will fall into your container). Now repeat until you think you have enough.
2. Now get your mortar and pestle out. Pour a small amount of your mixture into it. Grind it until you get a fine powder. This will also allow the pebbles with the ferrous metals inside to release them.
Step 3: Finish it all up...
1. Now pour a little bit of the powder into the lid. Shake the lid to spread the powder out thin.
2. Take the small magnet and place it inside another sandwich bag (at the tip). Now scan over the powdered mix, but don't get too close or you'll end up with some paramagnetic materials which are only weakly attracted to magnets (we don't want the weak stuff). So stay around .25"-.5" above the powder. This will allow the magnet to attract the ferromagnetic materials, while keeping the other away.
3. After you've scanned enough so that the tip is covered, place the magnet over the small container and pinch the tip of the bag (along with the metals) and pull the magnet away from the corner. The metal will now drop into the container (as long as you remember to let go).
Once you're done and there's nothing left to attract (except the paramagnetic materials), throw away the "dirt" and start the process again.
All the ferrous metal in the picture below was gathered and processed within an hour. Slow going I know, but saves a bundle. I'm actually in the process of designing a contraption to make this process faster and easier. But until then....Have fun.