I wanted the lid to look worn and ancient. I tried printing in a few different materials, but ended up going with plain white ABS for a couple reasons: first, the light bleeds through the white ABS in a super cool way.
Second, ABS can be finished with acetone vapors to smooth the edges and make the whole piece look worn down.
I placed my case's lid into an acetone vapor chamber for about 3-4 hours until it became smooth.
Next I sanded it down to get rid of all the shine, and added some nicks and scratches with a file and various other sharp tools I had lying around. I primered it with a paint-on primer from the hardware store -- a spray primer would have gotten into the grooves of the etching and blocked the light from coming through, so I did my best to keep those areas clean.
Primer is key. Don't skip this step! Hardly anything sticks to ABS, and my first attempt had the paint rubbing off after just a day or two of kicking around the house. I want this thing to survive grubby sticky hands at Renaissance faires so a little extra time now is definitely worth while.
I added a base coat of brown acrylic, then a base of Rub n Buff in antique gold. This stuff goes on thick and can be polished and shined after it dries, so it made a great base coat for underneath the acrylic texture. Wear gloves! This stuff never comes off your hands.
Next, I used a ratty paintbrush and a sponge to dab on low lights in gunmetal gray and metallic black, and then followed that up with some chrome silver highlights. Once I was happy with the look, I sealed the whole thing sith some spray polyurethane sealant since I expect this thing to go through some wear and tear.
Find a glass gem that fits inside the button hole without falling out. Craft stores have bags and bags of these in the floral section -- they're often used for filling vases to support flowers. Each one is a slightly different size and color, so it may take a few tries to find the right one.
My LED sequin needed a little more diffusing, so I soaked a couple circles of paper in crazy glue and affixed them to the bottom of the gem. To keep the light from bleeding through the case, I cut a piece of black vinyl shelf liner to fit around the gem and cover the electronics inside.