While millions of things have been dowsed with a simple brass key and a piece of thread, for those of us who use a pendulum regularly, we want something more.
Any substance will do, but I prefer copper or brass. I have a whole drawer full of trial and error pendulums including wood and crystals. What I have found is two things. First, weight. I finally settled at a 1 ounce pendulum. Second is the chain. I use a piece of 18k fine gold chain. This came from a scrapped necklass I bought from an old Jeweler friend of mine years ago. On the end of this chain is a 2.5 gram gold nugget I panned out of Yahoola creek in North Georgia. The chain is 7 inches long. The main thing about a chain is that it should be small and free making even the slightest oscillation possible.
Finding the weight for my pendulum was done with a small aluminum pendulum (very light) that had a witness chamber. I loaded the witness chamber with #10 bird shot a little at a time until I found the perfect weight for me. When I put it on a jewelers scale it weighted 1.014 ounces (troy). I like the spiral style pendulums as they seem to have great balance, but I searched and searched and searched and could not find a copper one. I finally contacted a pendulum maker in India and he made me a pure copper pendulum, in the spiral style.
When it arrived I put it on the scale and it weighted 1.02 ounces troy, perfect! Now I only map dowse with a pendulum for 3 things, gold, silver and platinum placer deposits. This pendulum has been worth it's weight in gold! (LOL, except for the copper part it is anyway)
So why spend so much on a pendulum? No reason except it is exactly what I wanted and you take much better care of an expensive item than a cheap one.
What I am telling you is this: experiment with different weights and chains until you find one that feels perfect for you, then make or buy one that fits the bill for your hand and needs. What is perfect for one will not work at all for another. That is why people try so many, they are searching without knowing it for the right feel. You can shorten that quest by weight and chain experiments!
Now your pendulum does not have to be gold and copper, in fact it may not even be metal but rather a crystal on silk thread. But it will have to be the right weight and the chain will have to be ultra fluid.
Finally, some sage advice from this old trogladite. Confine your searches to things of value to you. Gold, silver, water, minerals, herbs or if your a hunter, game and fish. NEVER, and that is with a capital N let someone talk you into hunting a missing dog, child or person. While things may work out just fine, coming into psychic contact with the dead is far from pleasant and it takes years to recover from such contact. Just don't!
I always refrain from dowsing auras as well. While this is less dangerous, one still picks up some pretty nasty vibrations from diseases and cancers. I place such things under "none of my business" and leave such to doctors