After building the stability upgrade to the Desktop Spectrometry Starter Kit, I needed to darken the exposed wood surfaces to reduce reflections and ambient light inside the spectrometer, which could affect the spectra we collect.
In this question, I posed some possibilities for darkening the inside, and although there are some other promising options, I thought I'd start with what seemed simplest -- painting the interior black, which took about 10 minutes.
Note that the current (as of Sept 22 2016) Desktop kit doesn't have bare wood, so this upgrade is really for those who've done the wooden stability upgrade.
I have some pretty cheap Sumi ink, the kind used for Japanese calligraphy -- I see Yasutomo brand ink for $3-7 per 2 ounce bottle online, which is WAY more than you need. I also used an old paintbrush -- this ink is water soluble, and while you shouldn't get it on your clothes, it washes out of the brush pretty easily. But you could use a cotton swab if you don't have a brush.
Sumi ink is really dark (hard to photograph, which is kind of the point), and importantly is matte -- no reflections. But you could also use a tempera paint, which is quite matte, and even easier to clean up. Finally, if you have matte black acrylic paint, you could paint onto metal or plastic surfaces, if you have some other spectrometer design than the one shown here.
I put a small amount of the paint into a jar to more easily wet the brush, and began painting it on pretty thick -- the wood absorbs it quickly so I just figured I'd get full coverage.
I painted it inside the box, since the new upgraded pieces are a little hard to get in and out, but you could paint it before putting it in the box and it might be easier.
I painted the whole area forward of the webcam; basically anything in the field of view of the camera. I could've painted right around the webcam, but figured there wouldn't be much reflection back there; if you do this, please tell me whether it makes a difference before/after painting all the way back.
I also considered taking off the DVD and painting the sides of the wood blocks which support it, but ultimately didn't. I'll post a spectrum soon and we'll see if there's room for improvement.
Recalibrate if you moved the DVD, webcam, or slit, then go ahead and start taking new spectra!
Anyhow, that's it -- pretty easy upgrade; please post below if you replicate it and share a link to your data on SpectralWorkbench.org! And -- if you have suggestions on how to improve this upgrade, or alternative methods, I'm eager to hear them!