Here I've done a technique where I laid multiple layers of colours on a surface and once it dried I proceeded to scratch it away. The deeper I went the brighter the colour. It's a bit of a tiresome work to do, my hand hurt by the end of it because of the pressure I had to maintain on the knife with each stroke.
The result though is one worth taking your time for :)

More: https://www.weasyl.com/submission/981593/in-trance