I just finished a project where I made a Tetris-themed yukata (finished pictures still to come). To do this I had to paint Tetris pieces on black fabric. This is my first time painting on black fabric, so here is what I learned by trial and error.
Prewashing the fabric will both clean the material and shrink the fabric so you don’t shrink it after you paint it.
A looser weave fabric will hold color less than a tighter weave. In order to get bright colors on a loose fabric you will need to use a lot of paint. This will make the fabric very stiff.
For my project I used a light-weight 100% cotton fabric.
I used Martha Stewart Craft Paint because it was in all the craft stores near me. It is an acrylic paint, so I bought a bottle of Fabric Medium to mix in. One bottle of fabric medium will last you a long time. There are many other paint options available, so if you have the time and money you can explore your options.
In order to make bright colors on black fabric I used a white paint to prime the squares before I painted over them with the color. In all cases the final color was a shade darker than the paint would be normally, even having been primed. I suggest using a scrap piece of fabric to experiment painting with different layer combinations of color. Let each layer dry to the touch before you put on the next layer.
I used one layer of white paint with one layer of color on top. This turned out well for most of the colors, except for yellow and orange, which sometimes required a little touch-up afterwards.
Heat set your paint when done to make it permanent.
The type of brush you use can be important. A fine-haired, densely packed brush will push more of the paint through a loose fabric, which means less color, but give you very even coat of paint. A coarser-haired, loosely packed brush will leave more paint on top of the fabric, which means better color, but can leave the finish streaky.
I recommend buying a large package of cheap bushes. I got 25 assorted brushes for about 7-8$ from my local store. It is also a good idea to use a leftover piece of fabric to test out combinations of paint and brushes on your fabric.
I picked up some ‘storage and solvent cups’ while I was picking up my paint. This ended up being one of the best choices I made. I was able to mix the paint and fabric medium in this container and seal it when it wasn’t being used. You can use any air-tight small container.
Cover your workspace with plastic. I got a yard of plastic from the craft store, and used it to cover the table where I worked.
As long as the paint is still wet I used a stiff-bristled brush with clean water and scrub at the paint until it disappears. It may cause some lint on cotton fabric. Use your best judgment depending on how thin or thick your fabric is.