I had a wonderful opportunity to be involved in beta testing Algorithmic Substance Alchemist, and what a tool! It draws you in and then makes you experiment more and more.
What you see here is a bunch of various material blends, and every blend has between 4 and 7 materials. Those materials are either photos I took or found on the internet or procedural substance files from my collection/substance source/substance share. You can mix all and any of that quite easily and iterate really fast. It's material doodling :)
If you would like to know more just watch the Siggraph 2018 - Substance Day Keynote on the link below. They keynote even features some of my tests.
Link - https://youtu.be/hlAxkJGeAT0