The first step is to secure all the components together in as tight a bundle as possible. I ended up putting the switch and the battery along the top side of the Feather, and then the matrix on the back side where it had room to shine.

Secure the switch and battery in place using hot glue. I ended up making the black battery cable a little bit longer by soldering an extra piece of wire in there, just so my battery could lay neatly beneath the USB port.

Melt a small amount of thermoplastic using a heat gun, or drop it into a pan of hot water. As it melts it will turn clear and get a little sticky. It sticks to itself really well, but doesn't stick to everything else. I used my silicone soldering mat underneath and it made a great work surface.

Once the plastic is all clear and melty, roll it into a little ball. Now you can start sculpting whatever kind of enclosure or shape you'd like. 

My next step was to press a ball of plastic underneath my glass lens. This adds a layer of diffusion between the eye and the LEDs -- the plastic will cool back to a translucent white and it will diffuse the lights nicely.

While the plastic was still a little melty, I pressed the lens down onto the matrix so it would cool in place and form itself perfectly over the matrix.

Melt some more plastic and keep sculpting. I found it easiest to roll it into a "worm" and then coil it around the lens, pressing and sculpting until the whole assembly was covered.

I made sure to leave the switch accessible, and added enough plastic that it didn't stick out and scratch my neck when I put the necklace on. 

I added a loop at the top for attaching my necklace cord, making sure not to block the USB port. 

The plastic cools to white, but can be reheated at any point and re-shaped with a few finger swipes. 

Thermoplastic can be painted but you need to use a good primer for plastic or the paint will flake off or not dry fully.

Cover the lens with modeling clay and the USB port with tape before painting.

Start with a good primer - I used Rust-oleum black gloss paint. A black primer underlayer will make any metallic coats look a lot more realistic.

Add metallic or brightly colored paints to finish. Most paints will stick to this primer. 

If your paint is still sticky after a couple of days, add a top coat of clear varnish or polyurethane to seal it. 

Add a necklace cord, and get ready to dance.