Thanks a lot, Greg.
The mix is close to how you have described it, intuition, experience, and, let me add, the willingness to fail forward.
The other part is observation and excluding the phrase “I know that” for good from the process. Why? Because it closes the mind off and accesses the illusion of memory.
So, how to do it then? I wish I had a tile of that stone here and could hold it into the sun. I have stayed four weeks near the Spanish Staircase (Piazza Di Spagna), where you have 32,300 square feet (3,000 m2) of travertine stone, and we were sitting there every day. You get an idea of that stone, yet when I googled it (avoiding the “I know that” stuff), I was reminded how many varieties there are.
However, something is always given: color changes, patches of more or fewer dents, while sometimes these dents are filled and polished.
I have used Noise options for over 25 years, and the options in the Node system to offset or scale those noises are very powerful.
Besides, just scaling one Noise axis seemed to be a good starting point. Then came the failing forward part, exploring what works and whatnot.
As you can see, I have some math nodes in it. The only general idea I can give is “information flow”, providing or excluding (mask/alpha) information or changing it. Some are for color, others to drive certain things. Also, here is the main idea, lean back and think about it. Can you express what you like to have in one sentence? If that is said out loud, you have a direction. Anything that doesn’t fit in is the failing part, or as someone said, we found 2000 ways it will not work. However: There is no failure, only gained experience.
So, it took me a while, but if I would invest more time, I would certainly include some sliders to explore a working setup even more.
The second suggestion I can share is if the work seems to lead to nothing, go with the current idea, and exclude anything but two parameters (max) and when that is nearly muscle-memory, go back to the complex setup.
Yes, that is not a tutorial, and certainly not a do-this-do-that thingy, which I think is not ideal anyway. But I hope my answer will lead to exploration and patience. Whatever you do and what isn’t working, you might find in the future some use—filling the Creative Library, as my philosophy is.
Enjoy.