Conservation Should Be the Artists Mantra
Since I paint on a lot of unique materials, I find myself having to adjust the chemistry of my paint. While artists traditionally use substrates like wood & canvas, many of us are pushing the boundaries by exploring new surfaces to paint on. Every artist should know a little about the chemistry behind their materials. While artists like Picasso occasionally painted on cardboard (which makes a terrible archival substrate because cardboard is full of acid), it is important to insure the longevity of your work both for your collectors and for your legacy as an artist. There is lots to say about the spectrum of proper archival methods but I will save that for another time. Instead I want to talk about adhesion and substrate, which falls under archiving. Surfaces like canvas are ideal for painting. The fabric grips the paint, absorbs, and ultimately bonds together. But what about glass, aluminum, and plexi? Those 3 are non-porous which means that the paint would sit on the sleek surface without any "tooth" to hold onto. Without proper steps taken, your paint would be at risk of being scratched or peeled off. Here is what I recommend for painting on these non-porous surfaces: First, you should use a scotch-brite pad to scour the surface. This will damage the shiny appearance of the surface but it will create "tooth" for the paint to grip to.
If you don't mind painting the entire surface white first, then I highly recommend Sherwin-Williams Adhesion Primer. It is an incredible product.
If you want to keep the background of your substrate natural in appearence, then let me introduce you to Golden's GAC-200. GAC-200 is a specialty primer that increases adhesion and film hardness. I recommend adding 30%-50% GAC-200 to your acrylic paint.
The best paint for non-porous surfaces will always be enamel but with the proper steps, you can begin to use other painting mediums with great success.