CG Education

Chrome Material
By Neil Blevins
Created On: June 19th 2002
Updated On: Oct 17th 2007

Here's a tutorial on how to create a chrome material in a number of different ways for 3dstudio max, although the theory will work for any renderer. I highly recommend reading my Metals and Reflections tutorial first, as it will discuss what a diffuse reflection is, a specular reflection is, how a specular reflection and a "reflection" relate to each other, etc.

Chrome

Polished Reflection vs Glossy Reflection

Polished and Glossy are two words I'll be using a lot in this tutorial. The difference is this...

A Polished Reflection is a undisturbed reflection, like a perfectly mirrored surface.
A Glossy Reflection means that tiny random bumps on the surface of the material cause the reflection to be blurry. Also known as a Blurred Reflection.

For more explanation see my Anisotropic Reflections tutorial.

Polished Raytraced Chrome

The basic ingredients are as follows:

No Diffuse (Black Diffuse)
Fresnel Reflections, IOR between 8 and 20

Here's the max file that made the image above, max5, brazil rio: polished_raytrace_chrome.zip

The first material in the file is a Brazil Advanced Material. Set the diffuse to Black. Add a falloff map to the reflect slot, set to fresnel, check the Override Material IOR checkbox, give it an IOR of 20. Turn off specular highlight if you want to use real raytraced reflections only and not light the scene with specular lights.

The second uses the Brazil Chrome Material. These materials are quite similar. The Chrome Material automatically has no diffuse, turn the reflections on, note that there's no IOR control, this material will be 100% reflective. While an IOR of 20 is ALMOST perfectly reflective, it's not completely, and so you'll notice a little of the black diffuse color peaking through on the Brazil Advanced Material. This material has none of that. Turn off specular highlight if you want to use real raytraced reflections only and not light the scene with specular lights. Note: the advantage of using the chrome material is that it's more optimized than the Advanced material (since it's been specifically written only for chrome), so it'll render faster. The disadvantage is that if you want to add a little diffuse back to your material, you can't, hence I would generally recommend using the Advanced Material since it's more flexible, but the choice is yours.

Remember, half of what makes a material look like a particular material is the environment it's in. A wise man said reflections only look as good as the environment the object is reflecting, keep that in mind. For this scene, I have a a smooth gradient from white (low) to black (high). I also have a few self illuminated white cards near the camera to appear in reflections. These cards have an output map in the diffuse slot, and a higher then 1 RGB level, which blows out the cards to values above white, making them appear brighter in reflections.

Glossy Raytraced Chrome

The basic ingredients are as follows:

No Diffuse (Black Diffuse)
Blurred Fresnel Reflections, IOR between 8 and 20

Here's the max file that made the image above, max5, brazil rio: glossy_raytraced_chrome.zip

Identical to the polished chrome above, except I turned on Brazil's Glossy Reflection Control, and set the Glossiness to 60. Now the reflections will be blurred. Play with the Max Error value to find the perfect balance between speed and image quality.

The Relationship Between Diffuse Reflection and Specular Reflection

In any real surface, the diffuse component and the specular component when added together must be equal to a value of 1. So if your specular is at a value of 1, or pure white, your diffuse should be a value of 0, or pure black, so together they equal 1, or reflect back as much light as it receives. In cg we can cheat this, however, the more we cheat it the less real the surface is likely to look. So in metals, since they have a strong specular reflection, you must compensate that by reducing the diffuse. That's why in the above examples the diffuse is always black or close to black, the more specular reflection, the less diffuse. For more info on Diffuse and Specular Reflections, see my Metals and Reflections tutorial.

Don't Use The 3DStudio Max Metal Material

Here's some tips about doing faked or environment mapped chrome in max. First off, a lot of max people think that to get good metal all you need is the metal shader inside the max standard material. Seems logical, it is called Metal afterall. However, I highly recommend not using the metal shader EVER, due to the complete lack of control it gives you over the look of your material.

The problem is that with the max metal shader, if you increase the specular highlight, it automatically reduces the diffuse amount. But wait, isn't that what we want? Well yes, we do want a material with a strong highlight and almost no diffuse, but the problem is the "automatically" part. The metal shader in max is a vast over-simplification of a shader known as Cook-Torrance. Such a simplification, that it takes too much control from the user's hands. As an artist, we need to be able to control that diffuse amount so that a material can look the way we want it to under many lighting conditions.

The problem manifests itself like this. You make a metal shader, increase the highlight, think it looks all good, but then when you place it in your scene, you can place a light an inch from your model, crank its multiplier to like 1000, and still only see the highlight and no actual object (see the example below). Well, to make this look nice, we'll need to add a slight amount of diffuse in. But wait, adding diffuse means the specular will automatically get less. But I don't want that! Well too bad, you used the metal shader! One quick fix solution is to have two lights for every light in your scene, a specular only light and a diffuse only light. But that adds unneeded complexity, not to mention slower rendering.

Metal Shader 1

The solution is to throw away the metal shader, and use blinn for your metal materials. Here's how to make the conversion. Here's the max file that made the images below, max5: no_metal_shader.zip Open the file and follow along with the instructions below.

Slot 1 is a max metal shader (such as the one on the left in the image below). If you grab the diffuse color swatch of the metal shader, and bring its luminance value up and down. Notice how the highlight grows and shrinks. Do the same with the ambient swatch. Notice the slight change in overall color. So basically, the diffuse color is now the highlight control, the ambient color controls anything that is not highlight, and you no longer have any control over the diffuse. So your material might look fine in your default lighting setup when you make the model, but in complex scene lighting situations, you'll waste countless time trying to tweak that lighting. So lets change it over to Blinn. Copy your material to the next slot. Change the second material's shader type to Blinn. Notice the changes, the highlight looks smaller, and the diffuse got brighter.

Metal Shader 2

So the second material no longer looks like metal, but now you have full control over both the diffuse and the highlight again. The first thing to try is to get back to something that looks like our metal shader using the Blinn controls. Reduce the glossiness to 50, and bring specular level to 250. Take at look at your highlights, they're now about equal. Now bring your diffuse color to RGB 35, 35, 35. Notice the two materials look very similar now. The difference being if I now want to add some diffuse back into the material (or remove it) once I start lighting, I can.

Metal Shader 3

So in general, to make a blinn material look like a metal material, make the diffuse color close to black, push your specular level to 200-300 (for a large intensity), changing your glossiness changes the size of the highlight.

Also note, the Brazil Advanced material also has an automatic feature that will decrease the diffuse as you increase the reflection amount. First off, this is based on much better math than the metal shader, so it's not a bad idea to use it, but if you really want the extra control, just switch the reflection mode from "Blend" to "Additive", now you can adjust the reflection amount separate from the diffuse amount. Just remember to try and keep that diffuse to specular balance we discussed before, or the material will look fake.

A final note, a guy named Michael Bailey did write an actual Cook-Torrance shader for 3dstudio max, available here. However, it's only available for max 4 and 5, it never got recompiled for max 6 or 7. Here's an interface shot...

Cook Torrance

Notice it has a specularity value as well as a specular level. If you need more diffuse color, you can reduce the specularity and then increase the specular level or index of refraction to keep a strong highlight while still retaining some diffuse shading, something the max metal shader can't do.

Glossy Environment Mapped Chrome

The basic ingredients are as follows:

No Diffuse (Black Diffuse)
Environment Map
Fresnel Reflections, IOR between 8 and 20, attenuated by a Shadow/Light Map

Here's the max file that made the image above, max5. It contains both a material for use with Brazil rio, and a raytrace material version for those of you who are using the scanline renderer in max: glossy_envmapped_chrome.zip Note that in the scene I used a raytrace material, but even though the name is raytrace, you can set it to not raytrace, and use an environment map instead. Just wanted to reiterate that a raytrace material doesn't always have to raytrace.

First off, what's an environment map? Well, when you're doing raytracing, your material is reflecting the environment in the scene. But sometimes your object isn't in an interesting environment, or you don't have the extra rendering time to do real raytracing, in which case you use an environment map. An environment map is just a 2d texture that is a stand-in for the environment. Otherwise, everything else is the same, you control the amount your material reflects, just instead of calculating a real reflection of your environment, it uses the environment map instead. Ideally your environment map should have the same general colors and brightness as your real environment, but it can also be more abstract. Here is the map I used as the environment map for the image above...

Env Map

I created this abstract env map using two gradients mixed together in max, but you can also use a bitmap painted or blurred in photoshop. This kind of abstract map works well for glossy reflections, but not as good for polished reflections, since you'd want a more detailed map of whatever is in your scene. For example, here's a rather popular bitmap used in reflections that comes with max:

Lake 03

Unless you want to blur this and use it as an abstract map, this map is really only useful as a reflection if your object happens to be by a lake at sunset.

So, back to the material. I have 2 versions, a raytrace material version for use with max's standard scanline renderer, and a version for Brazil. Both are basically identical. First, a very dark diffuse. Then the above environment map in the Environment slot. Then we need to turn off raytracing, so for the raytrace material, make sure the Enable Raytracing checkbox is unchecked. For the Brazil Advanced material, make sure Mode is set to Environment map.

Dialogue 1

Next, 2 falloffs in the reflection slot. Why 2, you may ask? Well, the first is our standard fresnel falloff to reflect the scene, but the second is a shadow/light falloff. What this does is makes sure it reflects the environment map only where the material's being hit by a max light. When doing pure raytraced chrome, you don't need this because you're getting a real reflection of your scene. Take the following example. Here's a reflective object in a simple scene.

Shadow Light 1

The environment is black on the right, and white on the left, and the reflection looks correct, since it's doing real raytracing. Now, lets replace the real raytraced reflection with an environment map.

Shadow Light 2

Wow, that material is glowing. It's because it's doing a fake reflection, and so doesn't realize there's a big black area on the right in the environment.

Shadow Light 2

Here's the material with the environment map, and a shadow/light and fresnel falloff. There's also an omni light on the left side of the image. While still a cheat, this cheat is far more convincing, because it's not reflecting the environment where there is no light.

You can also use a standard material to make chrome, however note that the standard material has a single reflection slot that holds both the thing the material should be reflecting (the environment map), and the intensity of the reflection (based on the luminance values of your bitmap). The raytraced material breaks that up into an environment slot, which controls what to reflect, and a reflect slot, which only controls how strong the reflection is using any black and white map (a colored map in this slot will also tint reflections, but that topic is beyond the scope of this lesson). I prefer using the raytrace material because it gives me 2 slots which means much easier control over my material, rather than trying to squeeze both functions into a single map like standard does. And of course, if using brazil, use the Advanced material, since it has similar controls to max's raytrace material.

Another note about Environment maps, instead of adding the map to the environment slot of your material, you can also place the environment map in the Environment map slot in the Environment dialog. This allows you to declare a global environment for all the materials in your scene. It will also show the environment in the background of your rendered image too, so if you don't want that, use the material slot instead. Also, if a material has an environment map in the slot, AND you have an environment map in the Environment dialog, the material will use the one in the material and disregard the one in the Environment dialog.

Glossy Environment Mapped and Raytraced Chrome

The basic ingredients are as follows:

No Diffuse (Black Diffuse)
Environment Map and Raytracing
Blurred Fresnel Reflections, IOR between 8 and 20, attenuated by a Shadow/Light map

Glossy Environment Mapped and Raytraced Chrome

Here's the max file that made the image above, max5, brazil rio: glossy_env_ray_chrome.zip

Here's the deluxe model, it contains an environment map AND raytracing. The idea being that objects in your scene will be reflected, however, you don't have to build an entire environment for your objects, you can replace any part of your scene that doesn't have actual geometry with an environment map. I use this quite a lot, it's sort of the best of both worlds, so I can build whatever I need to of my environment, have that reflected, and then have the rest taken care of with an environment map.

The same settings as above, except make sure the Mode is set to Raytrace.

Dialogue 3

With raytrace set, it will both raytrace, and if you have something in your environment map slot, it will also do environment mapping. If the slot is empty, it will only raytrace. And make sure you have the 2 falloff setup, since you don't want your environment map glowing.

Go here for information on how to do Brushed Metal.