This was cast in 1630, so it originally was all grey. The mold was also VERY poorly made with rubber that was not vac'd before pouring. Consequently, there were a lot of pits in the resin, and a pretty miserable seam.
I started by sanding down the seam, and filling in the pits with putty. The bummer was that by sanding down all the putty and seam, the grail got very smooth in a lot of parts. If you look at the pictures of the screen used grail, the surface is anything but smooth.
In order to break up the surface, I purchased a can of fleck paint from Home Depot and nailed the grail all over with it. The texture was a little too clumpy, so I took some sandpaper to it and wore it down a bit. Once I got a texture I was happy with, I sprayed it with Plasti-Kote primer, the red stuff. I then zapped it with a few random squirts of a candy apple red plasti-kote paint to give it some character.
The gold leafing was done using a gold leaf kit I got at Michaels. The trick is to dab on the gold leaf after you have wadded it up into a loose ball. This gives it a very organic feel without any hard edges.
Once the leafing had set, I sprayed some grey paint into a cup, dabbed a cotton ball into the paint with some added thinner, then just dabbed around the cup to give it that dirty, dusty look. I was originally told not to do this by a fellow builder, but upon watchin the film closely, I learned that it really did have a grey sheen to it.
I think it turned out really great. Although the leafing does not match the leafing in the film, you'd have to be holding the real one side by side with mine to be able to pick out the differences.