A big hello from PORTUGAL!

I Know that this is not fresco, but I'll ask this here because it's similar!

I need to know if dry pigments mixed with distilled water can be spread over watercolour paper to create a medium that will look and behave, when dried, like a pastel (I would like to make this because pure pigments have more chroma than pastels).
Can I fix a painting made like that with regular pastel fixative?
Can I paint with this kind of medium over canvas primed with universal primer (as long as I fix this medium)?
Can I paint with oil colours or acrylics over this dried and fixed medium? Or should I use this medium only over acrylics?
Thanks for your replies!
Nelson