Eldon, I've made a lot of goblets and all were made for use. For the inside I used locktite 2-ton epoxy from walmart. Has a slow set up time so I was able to work it plus it pumps out equal amounts from each tube (no guess work). I use a wood handled foam brush, the plastic ones break. Just don't play with the epoxy too much or the brush will fill it with small bubbles. 1 bush one goblet then start over.
On my walnut pieces I would start with just a little mixed with crushed turquoise and put a small puddle in the bottom, just enough to form a 1/2 inch or so circle or dot (it'll flatten out). Let it completely dry before applying the rest of the epoxy. Anything light colored will work just keep it pleasant to look at. It will help reflect the light when finishing the inside and save you from having to put a second coat on after you find that small spot you missed!
Sand it smooth on the inside and use a tacky cloth to clean out the dust just before the epoxy, you won't see it, feel it or notice it even if you clean with a moist cloth but start pushing sticky epoxy around and the dust literally comes out of the wood work. I pull my epoxy up and onto the rim and a small amount over the rim. sand the outside smooth when dry. Then apply several coats of a spray spar varnish sanding between coats.
I have several wine glasses at home that have been in use for more than a few years and have no problems. The only failure I had was one that had a small spot the epoxy didn't cover, the wine bled through and lifted the finish on the outside, repairable, and that's when I started using something light in the bottom for reflection and no problems since.
Good Luck!
Frank D