I did neither. I couldn't get good results by dropping it on top of the paint. Mixing the glass with the paint doesn't work at all. They loose all reflective properties if they are completely covered in paint so you need at least some of the glass exposed.
I found that sprinkling it on wet paint meant that it either sunk in too far or not enough of it stuck so I ended up with a shimmer on top of whatever screen surface was underneath.
In the pic, I had an undercoat which is aluminum ink (not paint) mixed with a little black paint which gave me a slightly tinted metallic surface. With a brush, I then painted a really thin layer of carbon fiber resin. This is basically a transparent epoxy. With a brush, I was able to coat the surface with a layer that was thin enough to leave most of the glass exposed. This kind of epoxy is sticky enough to glue an elephant to the ceiling. No joke, I really suggest gloves for this unless you are ok with a sand paper like consistency on your hands which may be uncomfortable in certain situations!
Before the exposure dried, I just tipped the bag of glass over the surface and tilted it until it covered every bit of exposed epoxy. It takes less then you might think. Only a thin layer of glass will stick and the rest will fall to the next but. When it is all covered, the remainder will just fall off when tilted and can be reused. Within 45 minutes, it will be rock solid. The next day, any excess can be brushed off and it's ready for testing.
On the increase in gain, it kinda depends where you are sitting. You need to be opposite the screen and ideally, on the same level at the projector. I was using it more as a translucent light diffusing layer to give me a watchable screen on a surface that would normally have been too dark. With the lights on, it gave me a really clear high contrast screen with amazing depth. With the lights off, it is noticeably a little brighter than the white screen. I saw a larger increase in gain when I applied the glass to a plan white surface which I also found to be a waste of time. In bright conditions, it isn't gain that suffered with white screens, it's contrast and even with greater brightness, blacks still look washed out.
One thing I would say about glass powder sized beads is that you do end up with a really smooth, but well diffused surface. Nothing like the visible sand like texture I have seen with larger beads.
I am always skeptical about the gain numbers claimed by commercial screen makers. They often claim a gain of 2.5 for their glass bead screens but the ones I have seen are all white and still look terrible with the lights on when using a dim home theater projector. Has anyone ever seen a white glass bead screen that looked good in a well lot room?
Either way, this method is cheap enough to warrant a few experiments if you are like me and enjoy that kind of thing.
