If you're trying to achieve things like gems then there is a tutorial on Youtube that they use ink from a ball point pen. Do what =LeaneaMee101 said too and get clear cast resin since they dry clear and not the opaque white which is shown in this tutorial.[link]
thats one of the youtube videos to get some ideas from and you can do your research from there. Always do a lot of research and small tests before jumping right into the project as a whole so you don't mess up.
good luck on your casting!