ANSWER: You can make a pendulum from many things, it doesn’t have to use a crystal, in fact many don’t!
I wouldn’t suggest using a hoodie string as it will be fairly thick and stiff but anything that is fairly thin and that hangs well by itself will work as a string. I have used necklaces with pendants, crystal pendulums, even a metal washer on a piece of normal string when times have called for it.
Rather than a crystal, you can use anything that has a little bit of weight to it and holds whatever you’re using as a string straight and swings freely. I prefer metal if I can’t use a crystal and preferably something that is naturally forming such as copper but it isn’t essential to dowsing practice.
I hope this answers your question,