This article is focused in converting theory into practice. We won't delve too deep into the theoretical part of how materials work from a physical point of view but will instead try to focus more on which parts of the theory are the most important for artists. There will be some more advanced practical tips but we won't also focus too much into practice.
Having a solid understanding of the theory behind light physics, is important for making more realistic and refined materials. Before you start reading this article it is strongly recommended to familiarize yourself with the theory behind Physically Based Rendering (PBR) - a concept that is going to persist and will be followed throughout all the examples below. There is a lot of information on the internet and you will find some links too at the bottom of this page - that's why there isn't a separate article here. A lot of smart people have addressed the topic already and my suggestion is to at least read through these couple of articles written by the guys from Substance:
The PBR Guide - Substance: https://academy.substance3d.com/courses/pbrguides
After you've finished going through these, you can continue to read through this article. Hopefully, most of the still unclear information from the Substance papers will be cleared here.
This article is focused on the Diffuse part of a material. You will find some information about the different types of diffuse maps, what the difference between sRGB and Linear color is and what are the recommended RGB values for proper Diffuse.
The IOR is one of the most misunderstood parts of a material. This article will illustrate the difference between Metals and Non-Metals and how their IOR is characterized. Furthermore, you will find information on how to create IOR maps - something that is rarely used but can boost the realism of materials.
The Reflection of a material is often filled with a texture - something that is totally incorrect. Following the previous article on IOR this one will shed even more light on how simple this component of a material is, how it works and how it should be treated.
The Glossiness map is one of the most artistic maps - it gives true character to a material, yet it is often forgotten. This article is about clearing some possible misconceptions regarding Glossiness and illustrates some ideas/techniques on how one can achieve a more complex and interesting map.
What is the difference between a Bump and a Normal map? What are the Pros and Cons and how to use these maps to their full potential? This article will shed some light on these questions.
Displacement might be quite heavy on your hardware, but it's totally worth it. This article showcases different displacement techniques while comparing the results they produce. You will also learn how to finetune your displacement to give the best possible results.
All the information in these articles illustrates the workflow used in most high-end VFX and Architectural studios. This is the industry standard and as such is meant to only help and facilitate the artists work. So do take the information you've read seriously but remember that even though some of these things haven't changed for the past 10 years, others could change a few times per year - you should always strive to look for the most current information and techniques used in the industry so you can upgrade your own skills. Good luck in creating some nice materials!
The PBR Guide - Substance: https://academy.substance3d.com/courses/pbrguides
Understanding Glossy Fresnel - Chaosgroup: https://www.chaosgroup.com/blog/understanding-glossy-fresnel
Mastering CGI Courses - Grant Warwick: https://masteringcgi.com.au/
Dubcats Secret Little Hideout: https://dubcats-secret-little-hideout.fandom.com/wiki/Dubcats_secret_little_hideout_Wiki
Map Explanations - Megascans: https://help.quixel.com/hc/en-us/articles/115000612165-What-maps-are-included-and-how-do-I-use-them-
Physically-Based Shading at Disney: https://disney-animation.s3.amazonaws.com/library/s2012_pbs_disney_brdf_notes_v2.pdf
GGX Shading Model For Metallic Reflections - Neil Blevins: http://www.neilblevins.com/cg_education/ggx/ggx.htm
Pushing the Limits of Realism of Materials - Maxwell Render: https://blog.maxwellrender.com/tips/pushing-the-limits-of-realism-of-materials/