Liberon makes what is essentially a shellac with a black stain in it (I have usually used it finials). If the object that you have turned is large, then you might want to dye the object black, and then finish with a black lacquer. It would probably require several coats. As another alternative, I have also used a black spray automotive finish available in most automotive stores. Essentially, it is a black lacquer mix. Spray light coats. I have had to spray up to five or six coats. Good luck with your project.
Matt