Let's use powder pigments to give the tablet a very believable stony/dusty look!
Pigments are just paint in its powder form, not mixed with any medium to create a liquid.
I usually use a round, soft brush for this. I take small quantities of the pigment and start rubbing it in randomly, as if you were applying make up.
Leave all the “specks” that fall from the brush as you are rubbing it, as this will give it a lot more detail. We will fix them to the prop later on.
I use Medium Rust from Ammo MIG for this step.