Depending on the paper most of my ink experiments have been water soluble. They have a great lift-ability. Which is great for sketching and drawing in many cases. However my ability to layer the ink to create deeper darks is limited because the ink lifts up into itself and actually ends up lighter when the brush lifts it off the page. Annoying. I’ve learned how to work with it, but what if I didn’t have to?
Gum arabic is an additive that improve adhesion to the page and improves flow, but it doesn’t seem to reduce the amount that my ink lifts off the page. In increased amounts it seems to simply thicken the ink.
Casein paint enters the chat.
Casein paint is water soluble until it dries then it is water resistant and in some cases waterproof. It’s about the correct blend of stuff to make it waterproof.
I’m more looking for water resistant than water proof.
From Robert Murray-Smith’s youtube I used this as a recipe:
- 100ml water
- 5g borax
- 10g Casein Powder
I mixed the 5g of borax into the water and let it sit until it had fully dissolved. This took just a few minutes with agitation. That is to say, I shook the bejesus out of it. I then added in 10g of casein powder. I added in a shaker ball I have for protein shakes. Again I shook the bejesus out of it. Then I let it sit for 15 minutes.
At this point I added an equal amount, by volume, of my homemade walnut ink.
Again I shook the bejesus out of it.
The resulting ink is highly water resistant and waterproof in some spots once dry. 
Again I’d say this is more like a liquid watercolor than ink. In this case it acts much more like acrylic or gouache than it does watercolor or ink.
It dries to a matte or satin finish depending on how much of the paint is layered onto the page.
I really like the paint and I can see myself using this to tone a canvas or panel or just for this sort of layered image. It is quite a bit more thick than the original ink. The casein glue is thicker than expected. I might need to acidify my casein, but so far this looks and seems pretty decent. My tub of casein powder will make a LOT of paint binder and DIY fixative. If I wanted to make this more ink like, I would test out amounts of the casein glue to add to the ink. I did 1:1 for the paint. But I think 1 part casein glue to 5 parts ink would probably yield an ink that was ink like and water resistant.
One thing to note, the casein has a very very strong odor of sour milk. It dissipates quickly when it’s dry or brushed onto the page but it is gag inducing when the dry casein powder is mixed with water.