Mastering Materials: Rust

Introduction

Since I started diving into the games industry back in 2008 I saw many rust textures in form of photos and images converted into texture maps which fell short from looking authentic due to hardware and software capabilities. Today as a 3d weapons artist I haven’t touched any rust materials whatsoever as weapon manufacturers coat each firearm with a thick coating, cosmoline and gun oils to protect bare metal from the elements.  

In this article I want to give valuable insights to help them achieve exceptional material definition.

In the realm of modern games, rust stands out as a remarkably intriguing yet challenging subject. What makes it particularly challenging? Inquiring about rust from various artists will result in many answers which will ultimately result in many different texture approaches. When viewed in PBR theory rust is often treated as dielectric material (non metallic). In this article I want to give valuable insights to help them achieve exceptional material definition. This involves a solid understanding of references and processes behind metal oxidation, the very process responsible for the creation of the "rust" as we perceive it. Furthermore, I intend to outline a strategic approach for seamlessly translating believable features from image references into the digital realm.

Understanding Rust

It is important to understand metals and what they are made of and which different types of metals does exists. In general there are two groups of metals; the one which can rust (oxide over time) ferrous metals and the ones which are not able to rust; non-ferrous metal.

Non-ferrous metals are metals which doesn’t contain iron in appreciable amounts such as; Copper, Tin, Titanium, Gold and Silver for example.

Corrosion Or Rust?

Some people believe that corrosion and rust is the same thing. Corrosion is a broad term that refers to the deterioration of metals of all kinds. In general, corrosion is the degradation of a metal through oxidation or other chemical processes. Rust is a term that describes the actual corrosion of iron and iron alloys.  

What Is Rust?

Many people don’t realize that rust (also known as iron oxide) is actually a chemical reaction.

A type of corrosion, rust occurs when iron, water, and oxygen combine to create hydrated iron oxide. The result is the crumbly, reddish-orange that we call “rust.” When rust occurs, it is actually the normal electrochemical process of metals returning to their natural unrefined state.  

Rust, commonly referred to as oxidation, occurs when iron or iron-containing metal alloys like steel are exposed to air (oxigen) and water over an extended period of time. Rust forms when iron undergoes the process of oxidation. Not all oxidation leads to rust. Only iron or iron- containing alloys can rust, but other metals can corrode in similar ways.

It is important to understand that the metal volume is growing due to the addition of mass on the metal surface (rust) which results in tensions during the corrosion. That’s why lacquered or painted layers peel form the surface as the rust is pushing through those painted layers. Furthermore the metal becomes porous, expands and blisters. The destruction process (corrosion) is progressing over time. Tensions arise (due to growing rust volume on the metal) and more layers of rust flake off.

Oxidation or rust occurs when the protective oxide layer on the surface of stainless steel is destroyed and there is a loss of electrons in the underlying metal due to oxidation combined with a corrosive aqueous fluid. Once formation takes place, it’s forming an orange, red-flaky coating that weakens the iron. Due to the existence of water in the equation, rust is more likely to happen on metal that has not been shielded against moisture. This is the reason why metals left outdoors, like older cars, gates, or tanks, are more likely to corrode. Especially when coatings or paintings tear down due to scratches or other collision damages.

Strategy Of Rust Creation

Reference Reading

It is easy to get overwhelmed at the beginning as there is so much to see and study - try not to start with a noise pattern first!

When searching for references or taking images you will notice that rust has a lot of information such as patterns, noises, bubbles, many colors and fine details. It is easy to get overwhelmed at the beginning as there is so much to see and study - try not to start with a noise pattern first! One of the main challenges is to avoid your rust material being too noisy. Planning your layers and folders in a logical order can help you creating your material without getting distracted by fine details or polish additions, which are better suited for the final stages of your work.

When approaching the creation of rust in a logical order, I followed a systematic process by thoroughly analyzing all the layers in my main reference to develop a strategic battle plan. This method allowed me to establish a logical hierarchy for organizing the layers and folders effectively.

0 - Clean plate, screw and plain washer as base geometry as foundation

1 - Metal and paint coating with various damages as groundwork material

2 - Dynamic rust layer to define the distribution and amount of rust

Since I wanted to create my own screw design I picked a slightly different one and started the analysis first by selecting larger details from those references as my primary focus. By prioritizing these larger elements, I ensured that the overall composition of the asset captured the representation of rust accordingly.

Additionally, I got myself into in-depth research on related topics, such as fungus on rust and its interactions with various surfaces. This approach allowed me to create a layer of authenticity to my 3D asset, ensuring that even the smallest details like spider webs were replicated.

No Preset Materials

It allowed me to maintain complete control over the artistic direction while adopting a highly procedural approach.

Since I don't favor third-party material presets, I took the entire process from the ground up, layer by layer. It allowed me to maintain complete control over the artistic direction while adopting a highly procedural approach. I often draw a parallel between this process and sketching a glass of water – the more you create it yourself from scratch, the more impressive the outcome becomes, even after replicating it over a thousand times.

Having said that, it's crucial to approach matters differently in game development, as you're unlikely to have the luxury of creating a procedural material more than once due to time constraints. Given that this is a LookDev project, I turned away from using any preset materials and limited my usage to just one or two custom imported maps. The majority of the work was accomplished using Adobe Substance 3D Painter resources.

Creation Of Rust

Is rust a metal or non-metal?

Due to multiple chemical reactions rust is a mixture of metal and non-metal materials. It does contain traces of iron but is not actual a metal since the physical properties of such are no longer present. Metal conducts electricity and energy (heat) which provides a certain color shift and luster which - after oxidation is no longer preserved.

Often metal surfaces and tiny spots are still visible underneath the rust layer. In between there are other layers of dirt, dust and particles and even fungus which can drop on top of rust. The decompose state will basically define how much metal is still visible which means you will likely have parts of metal, non metal and grey value definition in your metallic map to represent all those details.

First of all I created a working folder structure where I could put my feature layers into and be able to cross reference them with anchor points if needed. For a dynamic approach to be able to "live" paint the reveal mask of the rust it's essential to keep layer names and functions as clean as possible. In my project file, there are more than 40 references. To maintain a clear overview of each function, it is essential to be able to locate them without losing control over the arrangement of layers.

Anchor points play a crucial role, as I expect the need to retrieve specific height details later on.

Anchor points play a crucial role, as I expect the need to retrieve specific height details later on (Displacement creation). Furthermore, they prove valuable when working within a single layer stack, especially during expansion, where instances arise in which you wish to ensure that underlying layers remain unaffected -Levels adjustment for example. Using anchor points in combination with references enables you to effectively address and prevent such cases.

The main strategy involves a lot of color variation and moving on to the first larger details, rust height layers ( chippings) to bubbling pattern. Finally, attention shifts to noise distribution and small interesting elements like particles, dust, spider webs, or any other macroscopic features.

Noise Distribution

Noise is one of the most important elements in the creation process. This is particularly vital due to the fact that many rust textures and materials have either way too excessive noise information or employ overly uniform noise, resulting in a lack of clarity and structure of features such as bubbles, scratches, and other chippings within the material. Too noisy materials will hide your larger and smaller details. Also the essential amount of height strength is worth considering.

Gathering those microscopic detail images of rust thus taking photos myself helped me to get a sense for distribution of noise variants. Understanding the different sub-patterns and scaling of the noise is beneficial to achieve a realistic and well readable appearance of the material.

Roughness Texture

If someone were to ask me about the most important texture, I would say "Definitely the roughness texture!". In my opinion a material rises and falls with it’s definition, which is all about how a material interacts with light.

...a material rises and falls with it’s definition, which is all about how a material interacts with light.

Creating authenticity for the viewer is key to success. My motivation is to bring materials alive by establishing the haptics of a material with it’s roughness texture. I want to create the immersion for a viewer so they can actually feel the material while looking at it. In virtual reality (VR), this works really well since you're up close to everything. I want to capture that same feeling on a regular screen, as close as I can get.

By introducing many different variation in the roughness texture that correspond to the specular highlights of the material will create a great balance of details. Specular variation can help you adding depth and visual interest to the surface, making it appear more convincing and natural. Different pattern can enhance the overall quality and complexity of the surface. This is achieved by introducing gloss values to enhance finer details, while reducing gloss on imperfections and surface irregularities.

I experimented with layering multiple roughness textures and blending them together using various techniques such as masks, overlays, or blending modes. This approach can help simulate different surface properties or localized variations, adding depth and richness to the texture.

Summary

• collect as much references as you can and try to read the images with an artistic eye ( identify large, medium and fine details as well as nice touches for polishing)
• create a clean layer and folder structure with logic naming in Painter before you start creating anything - it will help you later on with references and finding features implemented
• take notes of the things you plan to avoid becoming overwhelmed right from the beginning - especially rust has many structures, layers and fine details
• if time allows start a material from scratch in order to retain max control of your layers and artistic direction - the more you build up from scratch, the greater your potential is to improve
• focus especially on the roughness texture to deliver the most realistic material possible - light plays a very important role in your definition
• take breaks and occasionally step back; it's vital for your mental well-being and creativity (I took several breaks and at times, I even began to re-do certain features if I wasn't satisfied with them during the process)
• it's okay to ask questions - actually do continue asking lot's of questions and stay curious
• feedback; seek feedback from others to gain fresh perspectives - the more the better and don't take it personal, most people around you want to help you
• experiment a lot, explore unconventional paths to discover new insights - avoid yourself from solely "working your way" and be open minded for new ideas

Thank you for dedicating your time to read through or scroll parts of my article! My sincere aspiration is that I have managed to offer you interesting insights and effective strategies for refining your approach to material creation. Breaking down the complexities of rust textures can be both challenging and rewarding, and I hope that the knowledge shared here will be valuable for many people.

About The Artist:

Malte Resenberger-Loosmann

Hard- Surface | Material | Artist Romero Games Ltd.

Artstation

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Company Workshops

In addition to the article, I'm thrilled to announce an upcoming workshop titled "Mastering Materials" that I'll be conducting exclusively for our company's internal teams. This workshop will delve deeper into the strategies and techniques of material creation, providing hands-on experience and interactive sessions to enhance your material skills.

Workshop Website