This Instructable will walk you through the steps required to copy a key just like secret agents do in movies. This includes making the impression of the key and casting it in zinc metal. Note that while copying keys that you own is absolutely fine, copying somebody else's key without permission or with malicious intent is almost certainly an offense punishable by law.
I really enjoyed the process of creating this key copy, mostly because I was shocked to discover that it actually worked. What had started as an offhand, careless afternoon activity turned into a viable copy of my house key. Enough small talk - let's begin key smithing!
As I said before, this project was not very planned. I was bored and wanted to make a copy of my key in one day, so I had to get creative in order to accomplish the whole process in one day. Thus, some of the steps listed here may be less than standard, but hey - they worked!
To copy the key, you will need an impressionable substance capable of withstanding the molten zinc at ~800°F. Plaster works well for this purpose, as shown in this video. However, plaster also has a bunch of water in it and takes quite a while to dry out completely. When pouring molten metal, you do not want water in your mold - it will create steam, bubbles, and possible explosions. So, in order to copy the key on one day, I had to figure something else out. My solution was very creative, to say the least. :)
I used dried-out carpenter's wood filler paste as the base material for my molding compound. It was the first good item that I saw around the house. If you replicate this project, you should mix around 3/4 cup of wood filler with a very small amount of water. Mix it well; it should be a soupy paste. Next, add some flour to your paste until it becomes thicker. Eventually, you should be able to remove it from your mixing container and then knead it like bread dough.
Note: This project is not gluten-free. :)
After you have kneaded your dough until it is soft and well-mixed, it should feel just like a good hunk of bread dough.