Recipe: Take half of tea-spoon (flat) of casein for two cups of water. If you are aiming for a rougher texture then put more casein powder and less water,
but maximum one teaspoon for one cup of water. Mix well and let it sit for 10-15 minutes.
In a separate bowl mix the natural color. For this purpose, you can use watercolor or ground sepia powder with water.
Make sure to mix your color separately, so that you can add gradually to the casein mix in the desired amount to reach the intensity of the color you want.
Take an industrial roll (the one you’d use to paint the walls in your house) or wide industrial brush or a sponge.
Stretch the paper on the board. Shake casein mix and add in the color mix to it.
With wide and large moves cover the whole surface, using the roll, big brush or sponge, spread the mix on the paper evenly.
Leave the primed paper on the board to dry completely.