Response by: Majinko, July 17th 2017 5:10:39 pm
Chloe has a great suggestion but I would recommend a few tweaks. I would not use Plastidip as in my experience, that does not bond very well to smooth surfaces.
I would suggest:
Make the cape in yellow and then coat one side in black. It's easier to make one side black with less latex applications. To do this, use liquid latex, which is available in bulk on Amazon for about $7 for 16 ounces (which will be more than enough), and mix in black acrylic paint. The liquid latex will dry darker than the mixture's color so try a test patch to perfection your ratio.
Be sure to thoroughly clean and dry the side you intend to paint black so the liquid latex adheres to it. If you find it is not sticking to your liking after your first few applications, light sand the latex and try again. You can also use a solvent to loosen up the pores on the latex but that will make creating a smooth finish slightly more laborious.
When applying the latex paint mixture, use a bristle brush and do thin coats in one direction. Before the coat completely dries, apply another layer in a perpendicular direction to create an even finish. Continue building light coats until you can no longer see the yellow. Then apply a few more to make it final. Once dry, the black latex will have bonded to the sheet of yellow latex and should last indefinitely. You can perform touch ups to the finish as necessary. It'll be far easier to match your black paint than it will the yellow, which is why I suggest painting a yellow side black. If you start with black and paint it yellow, it will take more applications, more paint, and will be harder to match.
I hope this helps, keep us posted!