While waiting for Zaks ditty, some ideas for the shields.
Top row the disc cut from thin aluminium, and a hole cut in some paper/card. Middle row paper fastened to disc and bottom row paper cut at the edges of the disc.
Works OK but will have to make a lot to be able to choose the best, and will also try and think of another way to do it. Might try and fasten a bit of solder around the disc edge and see how that goes - suppose I could just paint a ring on the risc edge but would be best if it has a slightly 3D effect