I have tried hide glue with good results except with charcoal pigment, wich seems to somehow hinder the glue from hardening. It still will, but much slower. One probelm I had was that these paints clogged up my brush. I soon used a wood shaving instead with better results.
But since the glue is a watery solution, you cannot really paint over oiled surfaces.
I have also tried egg white. Not bad results, but the stuff tends to lump, and it pulls into strings instead of a little bit remainig on your brush. A bit of cream will solve that, but extend the drying time
I have also used curd (take the low fat variant). This stuff is brillant, but it tends to have a white colour by itself turning all colors into pastel. Works pretty well with charcoal.
All of these are not waterproof. If you want a waterproof primitive paint, there is no way around adding resin. Since resin does not solve in water, it is a bit complicated.
I have used powdered limonite, mixed with curd, linseed oil and pine resin about 20:1:2, and got a nice, easy to apply yellow paint that was as good as waterproof (though it was still possible to rub it off). The resin was heated and mixed with the oil first.
Last week, I have experimented with clay that contains iron and powdered oak bark, and I'm quite confident this will make a good black ink. I'm not quite happy with the clay as a source of iron, though (now that I write this I realise I should try the limonite)
Also, there's all kinds of coloured juices and saps. They come in reddish tones mostly, like berries, but will turn brown eventually.
