The kind of string you use for fishing....nylon. You need to use a really thin string so that you can string it a couple of times for strength.
Otherwise it's easy.
About the promised tute...I don't think I can make it. I tried yesterday to make it all over again, but I can't figure out how I did in the first place.
I made that brooch improvising as it came along...
You're welcome to copy it, but don't ask me how