Did you check the body of the piece for an artists signature ?? I have looked everywhere and have found nothing similar nor has the 618 number ever shown up in the searches !! I would suggest taking this to a good auction house for valuation !! Just don`t leave it there !! I have a concern about the markings on the bottom and there is always the possibility of a fake but I would hesitate to say that it is or is not Rookwood !! But there is nothing that shows up with this form !!
If you find out for sure please come back and update this post !! I am very curious !! Sorry I couldn`t be of more help !!

Oh yes !! These pics are much better !! The first pics looked like a matte glaze and I wondered about that !! There are several mentioned as a two handled vase !! And that is what I am assuming this is !! Still trying to track it down !!

I am posting a photo of the front and rear of the piece.

Thanks for the information. My husband gave this to me for Christmas 10 years ago. He found it in a small collectable’s shop.

http://www.treadwaygallery.com/6-5-99-sale/catalog/

Did not fine you vase number in this list !! Found 616 but not 618 !!