What is a V-Ray Material Made Of?

Understanding what makes a realistic material

01. Introduction – What you’re going to learn

Materials are made up of several different components and in the end, these components come together to form a full material. You can adjust the values using simple colors but for most materials you will need to use image maps. Afterwards you will see how extra realism comes when showing objects with a subtle bit of use and wear on their surface. In this section you will be learning about all the individual pieces that come together to create a realistic looking material.

Example of metal and wood materials with surface variations for added realism


02. What is a Material?

A material tells a surface how to behave when light interacts with it. Does the light pass through, does it reflect, does it get absorbed? If you modeled a cup without a material and hit render it would just look like a cup shaped object with a solid flat color. A material can make that geometry behave like anything from polished glass to old, weathered wood.

The VRayMtl node is a blank canvas material that is specifically designed to work with V-Ray. All materials that you will create will use this node. It allows for physically correct illumination in a scene with faster rendering. This material can be easily set up to simulate a huge variety of surfaces from plastics to metals to glass and more by adjusting a handful of parameters.
Furthermore, with the VRayMtl you can apply different texture maps to parameters, control reflection and refraction, add bump and displacement maps, and much more. Learn more about V-Ray Materials here.

a. The basic elements that make up a material are:

Diffuse – The base color or pattern that defines the object, i.e. is it green or blue?

Reflectivity – How much light it bounces back. Does it have a mirror finish or is it dull?

Reflective Glossiness – The clarity of the reflection and highlights seen across the surface.

Refraction – How light bends as it passes through a transparent object (not the same as opacity).

Refraction Glossiness – The clarity of the refractions seen (think clear or frosted glass).

Bump – The surface characteristics that give it texture you can feel. Wood grain, fabrics, scratches, etc.

BRDF Shader – How the highlight behaves (crisp edges or soft and feathered) in the rendering engine.

We will walk through the elements that make up materials more before moving on to creating one.

b. Basic parameters of a VRayMtl Node

All of the elements mentioned above will plug into the VRayMtl. From here you will set the values of the material you are building. We’ll go deeper into some of these later when building materials. For now, know that the color of the text relates to the color of the box on the image to the right.

Diffuse will set the surface color of the object or tell the material to use a map (texture image), indicated by a capital “M” in the box. If you’re using a map, but have it disabled it will show a lower-case “m” instead. Roughness gives the surface a flat, or dusty, appearance but isn’t the same as changing reflectivity.

Reflect color will be a grayscale value in most cases unless working with certain metals. Avoid using pure white or black as nothing is completely reflective or without reflection. The lighter the value the more reflective the surface is. H.Glossiness stays locked, R.Glossiness should always be .98 or less because nothing is perfectly glossy. Max Depth controls the amount of times a light ray is allowed to bounce off of this material and can usually be left at the defaults.

Fresnel Reflections should always be checked and unlocked (click the uppercase “L”: in this image it is shown as locked). This controls the spread of the reflection across the surface depending on viewing angle. Think of it as pulling the reflection closer to your view, so a polished metal would be between 18-50 because it’s entire surface is reflective. While a polished wood or leather surface would be around 4-6 because it’s only more reflective at grazing angles.

Translucency doesn’t get touched unless working with materials that require light to penetrate its surface. Candle wax is a good example.

BRDF controls the softness of the highlight across the surface independent from the R.Glossiness value. There are older methods that are sometimes still used, but the newest and most accurate is GGX. Values between 1.6-2.2 usually work for most cases and really should be changed for artistic purposes. Generally you will only need to set this to Microfacet GTR (GGX) and that’s it.

Anisotropy/Rotation controls how the reflection stretches across the surface. Some metals distort the reflection and give it a radiating rotation appearance (like a stainless steel pan). We’ll cover this more later.

03. Determining a Material’s Basic Surface Details

Learning to look at an object in the real world and visualize the different elements that make up its surface is going to make creating materials a lot easier. After that it’s just about just blending those elements together to find the combination that creates the look you need. When you start working with a lot of materials you’ll start to notice the similarities shared in those values.

For example, the image below looks like wood – but take away the color (diffuse map) and it would still look a bit like wood because it has a bump map making the surface look rough. This surface has many different elements – roughness, reflection and color – that combine to make the final result. If you only used one of them it would not be realistic. For example, if you used only the diffuse map then the light would not bounce off of the wood grain. This would leave the color looking painted on and unrealistic.

Let’s get into detail on the different elements that make up a material…

a. Diffuse Maps

Below are some examples of what you would place in the diffuse map of a material. These are images that will show what the surface is made of. They should be flat lit images, preferably seamless (which means they can repeat and you can’t tell where the edge is), and not show obvious highlights or shadows. If the reference image does have these there are tricks in Photoshop to remove them.

Here we are showing wood grain, but no other maps are telling us if it’s reflective, bumpy, glossy, etc. The material looks flat and unnatural.

b. Reflection Maps

This controls what areas of the surface are reflective or not. It does not control the clarity of the reflection seen on the surface. Darker knots in wood grain are not as reflective as the lighter grain, fabrics can be a mix of dull and reflective threads. These are generally black and white unless the material is a conductor of electricity (gold, copper, other metals). These materials will reflect back color because they’re creating energy from the light, and if your map has some color in it it will reflect back that color in the final render. The reflectiveness of a material can also be controlled using the reflect channel color. White = Mirror, black = not a mirror. Remember though that nothing has a perfect surface and you should use a map in the reflection channel to show use.

Here you can see the darker grain of the wood isn’t reflecting back any of the background pattern (especially on the top of the cube). If this were a metal the map on the top right would reflect back that color variation.

c. Reflection Glossiness Maps

Often confused with Reflectivity, this controls the clarity of the reflection seen and not how reflective the surface is. The texture map controls how much the light will scatter when it hits the dark areas of the texture. Light that scatters will produce wide, soft highlights and light that bounces off and does not scatter will have sharp highlights. Highly reflective surfaces have smaller, sharper highlights, duller surfaces have larger, softer highlights.

The image on the left does not use a gloss map but has a very high glossiness value. The image on the right has the same glossiness value but uses a map to make some areas of the reflection more or less defined.

You can also adjust the overall reflectivity of a material by adjusting the RGloss value. In the images above, the left image has an RGloss value of .99, while the one on the right has a value of .6. Notice how the object is reflecting the same amount of light, it’s just the sharpness of that reflection that’s changing.

d. Bump Maps

These are black and white images, sometimes just black and white versions of the diffuse map with higher contrast, that show elevation differences (cracks, wrinkles, coarseness) in the surface. These do not affect the geometry though.

The bump map is telling the light that the darker grains in the wood are deeper, causing the lighter grain to catch the highlights and cast shadows. For bump maps, white is up, gray is flat and black is down. They only give the appearance of distorting the models surface. Displacement maps distort the actual geometry and rely on the mesh to be more dense to get those details.

e. Displacement Maps

These are very similar to bump maps – you can even use the same maps that you would use for bump! However, displacement maps are used to physically distort geometry, instead of just creating the illusion of surface detail. They also differ in that they are only positive: black is no change, 50% grey is 50% height and white is raised. Black does not make geometry go “inwards”.

Displacement maps are especially useful when the silhouette of the model needs to change but it would require a lot of modeling to create that physical detail.

f. Normal Maps

Normal maps are similar to bump maps except they use specific color values to indicate height and angle to viewer. So instead of just up and down you now have bumps that can go in all directions. Photoshop offers a quick method to create Normal maps from images under Filters>3D>Generate Normal Map. These maps produce more realistic results than bump maps in more lighting conditions.

04. Adding Variation Using Grunge Maps

Things that look too clean and new in 3D can often look fake because nothing is ever as clean as it can be in 3D. By adding “grunge” or “dirt” textures to these nodes you can add wear and character to the surface. It’s important. We don’t want products look beat up, but to look somewhat used. Plates being slide across tables, cushions sat in, mirrors wiped with a towel. All these actions add life to a surface and a little variation in reflectivity and glossiness really goes a long way in making something look photorealistic. In the image below, a grunge map has been added to the Reflect Glossiness channel.

And you’re not just limited to one grunge map. You can combine several with different tweaks to get an infinite amount of variety. Notice the quality of the reflection on the top of the sphere – it’s still shiny and looks new, but it also looks like it has seen a little real-world use.

05. Other Material Options

a. Fresnel IOR

As explained above, Fresnel (pronounced “Freh-Nell” – it’s French) IOR will wrap a reflection around an object. Below are some examples – on the left we show an IOR of 1.6 (which is common for most materials) and on the right we show an IOR of 40 (typical for a metal).

b. Microfacet GTR (GGX) Shader

This is the shading methodology at a high level that controls how light bounces off a surface. Below we are comparing two different versions of the shader: on the left is 1.3 and on the right is GGX 4.0. Note that this is the same material with the same settings, minus the shader type. GGX 4.0 is creating a sharper transition between light and dark on the reflection of the surface, creating an overall crisper reflection.