When you are working with metal, whether casting, on the lathe, or by hand you will get slag and flash. This is a simple way to reclaim those leftovers back into useable metals.
Step 1: This Is Slag
Slag is oxidized metal or impurities that must be scraped off the top of melted metals. If left in it is both unpleasant in appearance and can weaken the finished product significantly.
Step 2: Collect All of the Slag Into a Pile
Using an old stainless steel bowl or steel pie plate. Pile all of your slag into a loose pile.
Step 3: Borax
Add about two tablespoons of anhydrous borax into the mix with the slag. This will both lower the melting temperature of impurities (such as iron), accumulate much of the slag in a molten glass-like substance.
Step 4: Get Your Torch
I prefer to use MAPP (a fuel gas based on a stabilized mixture of methylacetylene aka propane and propadiene) you can also use propane alone but it will take longer since propane burns less hot.
--- Warnings ---
Please only allow adults to handle or use torches or open flames.
Do not try to use these products in bright direct sunlight, the flame is blue and is not visible in some conditions.
Use in a well ventilated area and have a CO detector.
Follow all safety instructions on the bottle / MSDS.
Step 5: Caution
Be careful as you begin to melt the borax, if you point the flame directly at it the borax will blow all over the room. Be prepared because it will happen some regardless but it's the difference between a little and almost all of it.
Step 6: Melt
As the borax begins to dissolve move in with the flame more. Get the entire pile to red hot.
Step 7: Shift It
Using stainless steel tongs carefully tip the plate to one side. Soon a small stream of metal will begin to run away from the slag.
Step 8: Finished
Carefully remove the leftover slag and allow it to cool before disposing of it. Pour the useable metal into a crucible or form to allow it to cool. You can then remelt and refine further if you wish.
This method has worked well for me in the past. It usually yields 4-6 ounces out of a pound of slag.