Is there an "industry standard" way of getting the BRDF equation from actual real world materials?
Or do I have to just manually play with the parameters and equations for the BRDF until it approximates what I see in real life?
I'd imagine there are some kind of expensive devices that make rough BRDF equations of real object, but I'm curious what the go-to solution is...
Hi, the follow paper's Intro and Related Work sections discuss some methods to obtain BRDFs: https://cseweb.ucsd.edu/~ravir/tisbrdf.pdf.
As I far know, there is no one "industry standard" that everyone uses. The BRDFs used in computer graphics can be either computed from theoretical models or captured. For example, "Data-driven BRDFs" are obtained by using empirical measurements and then trying to fit a mathematical function to the data. Simple, theoretical models such as Blinn-Phong can have their parameters changed, which, as you observed, is a tedious but surprisingly practical and accurate process (this is most likely due to the fact humans are not very sensitive to the small details present in materials)
However, the models don't always need to be physically-based. Disney developed a BRDF model that was a "principled" model rather than a physical based one. You could read more about it here: https://disney-animation.s3.amazonaws.com/library/s2012_pbs_disney_brdf_notes_v2.pdf
In terms of the different types of material, one thing I found was a mixture of the different types of reflections in certain materials. Here is a diagram depicting what a mixture between diffuse and specular reflection would look like: http://www.vacuumcoating.info/wp-content/uploads/2011/09/RW_Fig1-450x138.png