Need help identifying this old deep amethyst glass decanter or ink well?

Hello everyone,
I would love to know if anyone can help me identify this. I am not exactly sure what it is or what it was used for. I thought maybe a decanter or a large inkwell. It is a deep dark amethyst color and hard to see through it. When you hold it up to the light you can see a "thumbnail" type pattern in it and you can see the color better. The outside of the glass almost looks and feels oily. Any info would be helpful. I am also looking for the maker and the possible age?
Thanks So Much!!!!