Skill Level Intermediate
- [Instructor] The Arnold standard surface material can produce iridescent effects, using a feature called thin film. It's modeled on the physics of a soap bubble, or very thin films of transparent material that may only be a few molecules thick. The thin film feature can also be utilized to produce other kinds of iridescent effects, such as the back of a scarab beetle or metal flake car paint, or in this case, ceramic glazing that has a metallic or crystalline component to its chemistry.
Let's open up the material editor and assign the Arnold standard surface material to this model. We'll go to the material editor from the main toolbar, and I've got a stripped-down version of the material editor just to keep things simple for the demonstration. I'll create the Arnold standard surface material by right-clicking in the view, choose materials, Arnold, surface, standard surface. Double click it, to load its parameters and rename it iridescent glaze.
To assign it to the geometry, let's open up the scene explorer, got that on the main toolbar here. Toggle scene explorer, and select athena body, hold down shift and select athena helmet, which also selects the hair. We can go back to the material editor. And with that iridescent glaze material selected, click to assign the material to the selection. Okay, we can close the scene explorer and then open up an active shade window, I've got that prepared already.
Click on active shade on the main toolbar, and it renders the Arnold standard surface with its default parameter values. Let's start changing those. I'll go over to the base color and increase that to its maximum of one, but give it a very dark color for the base of this material. So click on the color swatch, and let's set the hue to the blue color, making 0.65, saturation up pretty high at 0.9, and the value very low, 0.03, so it's just barely producing a little bit of diffuse shading.
This is going to make the iridescent effect more dramatic, against the dark background. Moving on, we've got the specular components here. In order for the iridescent effect to work, either the general specular amount must be non-zero, or the metalness must be non-zero. If they're both set to zero, you won't see any iridescent effect. In this case, I'm going to increase them both to their maximum of one. This'll make it very dramatic.
And even without any iridescence, we're starting to see the effect of changing the metalness. We're getting these colored highlights. The index of refraction for the specular component is significant. But since we've got a metalness of one, that's overriding the IOR here, so since I have a metalness of one, the IOR doesn't really do anything. But if you have a metalness value that's less than one, as you change the IOR, you'll see the iridescent effect change.
I also wanna give it a little bit more roughness. Let's set that to a value of 0.5. And now we've got a very subtle effect of a metallic look here, and we got a dark enough background that we can actually see the thin film. To access the thin film, let's scroll down in the Arnold standard surface parameters. And here it is, thin film, and it has an absolute thickness in nanometers.
So it's going to have a valid range of somewhere between maybe 100 and 2000 or 3000. So this is a physically modeled parameter. Likewise, with the index of refraction, that would need to be something in the range of one to maybe three, in order to see any effect. Let's give this a thickness of 400. And now we're starting to see some iridescence. I'll also increase the index of refraction to 1.8.
And because we've changed the index of refraction, the hue actually changed. And again, this is a physically modeled effect. And if we had a thin film that was 400 nanometers thick, and had an index of refraction of 1.8, this is the hue that we would get. We could make this more realistic by varying the thickness across the surface. I can close my color selector here, and add a map here to the thickness. But I can't just connect any old map, because I need to have a range here of 400 or so and a standard map only gives a range from zero to one.
We need to pipe that through a range node, so once again, right click in the view, this time choose maps, Arnold, math, range. Take that and connect it to the input of thin film thickness. I'll set my view to a 100%, just to make that easier to see, and then middle mouse drag to pan around. Connect this to thin film thickness.
And now the range is just sending out a value of zero cause there's nothing connected to it. If we double click on that range node and load its parameters, we can change up the output min and output max. Those are the values that will be feeding into the thin film thickness parameter. Let's set the output min to 350. All right, now we're pushing that value up from zero to 350. Let's also set an upper limit here. We'll make that 400, for the output max.
In order to see a difference here, we need to supply a map, so once again right click, choose maps, Arnold, texture, noise. And once again, connect that. Take the output of the noise and plug it into the input of the range node, and we start to see a pattern. Double click on that noise node, and just change its scale. Let's set the scale values in x, y, and z to 0.1. 0.1, tab, 0.1, tab, 0.1 and enter.
And if we really want to go crazy here, we can start playing around with the lacunarity and octaves and so on, but for now, we can see that there is a variation in color across that surface. If we wanted to exaggerate that just for the demo, we can maybe increase the amplitude up to something really high, like 9.7 or whatever. And now we can see there's some clear delineation in the map. Right, I'll bring that amplitude down to something a little bit more reasonable, maybe a value of two. We've seen how the thin film interacts with the specular component of the material.
It will also interact with the transmission component, and with a clear coat, if any. Let's take a look at the clear coat, as if we had our thick layer of glaze on here. So go back to the iridescent glaze material that we created, and we want to find its clear coat parameters, so we'll need to scroll down, clear coat, set its value to one, so that's the strength of the clear coat. Set its roughness to 0.3, and we've got the index of refraction for the clear coat.
Let's set that to the same value that we chose for the thin film, which is 1.8. And now we've got a pretty realistic effect of a layer of glazing, that includes some metallic or crystalline component to it. And that's how to use the Arnold thin film parameters in order to achieve iridescent lighting effects.