Two step: shadows on ink and then watercolor!

Today I learned something. I followed Robert Muts tip and solved something I had no idea how to do: How to place shadows in a watercolor piece without muddling the color when it mixes with the darker hue. .
Possibly there are many more sophisticated ways, but this one works wonders for my needs. Instead of adding darker watercolor over a brighter one -or the opposite- Robert suggested I paint the shadows with ink, and then watercolor over it. 
As the ink is fixed, it does not melt, and the watercolor over it is perfectly saturated. 
Of course this is a crude example I did as a test, and don't ask me what this is. It's just a thing full of angles and shadows.
Also I drew -and painted- it twice, one with china ink and the other with Noodler's black Bulletproof. I don't see much difference. 
This two step is before and after coloring, quite obviously....

Then I made a real sketch. I always wanted to paint the night, and had no idea how to do it. His method does wonders. First shadows in ink and THEN watercolor. 
This a photo I took on Bologna last year. I always wished to draw an image like that.  That's how to do it.  Thanks, man. 
..
Esta es una idea de Robert Muts para que no se empasten las sombras en acuarela. Primero, dar sombras en tinta china, y despues colorear encima en acuarela. 
Los colores no se mezclan, ya que la tinta esta fija. Una maravilla.
Hice dos pruebas, en tinta y china y Noodlers, ambas diluidas en agua. no veo diferencia...
Despues hice un dibujo en serio, sobre una foto de Bologna del año pasado.. 
Siempre quise dibujar "la noche", y ahora siento que encontre el metodo.