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..::terracotta material::..

Technically, it’s the same kind of material that bricks are made of; traditional terracotta is a lot darker and “aged” than the commonly used type today. That out of the way, the first suggestion I would give is to use a texture map of a pot and wrap that around your mesh. But if that’s not feasible due to complex mapping and the like, then we can create a procedural material with a bit more effort.

But why is it more effort? A material like this isn’t just a single coloured matte material, it’s a combination of varying specularities, texture, and colour. Take a close look at a terracotta pot that has been out in the garden for a few weeks and you’ll see that we’d have to create damp marks, the texture of the pot itself, changes in colour where these textured surfaces have scraped against adjacent objects thus revealing a lighter shade. All these elements justify the use of a texture map, even if the base texture is procedural, to get the effect bang on.

We will start out on a standard object in the shape of a pot. Instead of using a standard primitive, such as a teapot or sphere, using an object that has the material we are trying to emulate gives us a good comparison when working. As with all emulation in CG, try to get an example of the real thing in your hands to see exactly what is going on. We are also working in a scene that has a lighting condition in which the object would be situated – daylight with a bright sun. For this example, we are using 3ds max 5’s Light Tracer (with low preview settings for speed) for GI and a Direct light for the sun.

The colour of the material varies over the object; we don’t have a single colour, but multiples thereof. Slight variations suggest imperfections in the design and weathering; a clean single colour would look totally out of place and would suggest that the object was fake. If the pot has been used before or has been out in the rain, chances are that there will be darker water marks over the surface, hairline cracks caused by changes in temperature, mildew and mould over the surface and so on. It should also be noted that some designs are shinier around the rim, while the sides are more textured and matted. Some are glazed inside and are smooth around the base, so adjust and mix materials together based on your preferred design.

Most, if not all have imperfections due to mass production. These take on the form of collections of ceramic material around the sides in the form of tiny raised areas which can be simulated using procedural maps. In addition, the sides are slightly bumpy, which is also due to the manufacturing technique, and can be simulated using small Noise procedural maps. If desired, instead of using bump mapping for these small nodules, displacement mapping could be utilised to produce effective results.

Because of dust and debris collected on the ceramic surface, we would also need to create a slight falloff around the edge depending on lighting. This can be generated using self illumination and/or falloff maps in the diffuse slot that are mixed with the main colour(s) to create a white (or otherwise) falloff around the perpendicular if there is light present.

Overall, this is a relatively straight-forward task, provided we analyse every element and build it up from the base colours, to the imperfections, to the water marks, to the dust and lighting effects.

Enlarge Screenshot Load in the terracotta_start.max file. In the Material Editor, label a new material “Terracotta”. Set the Specular Level to 20 and Glossiness to 15. In the Diffuse slot, add a Mix map and label it “Watermark Mix”. Add a Noise map to the this Mix map’s Mix Slot and label it “Watermark Control”.
Enlarge Screenshot In this noise map, set the Noise type to Fractal, Size to 20, High to 0.75, Low to 0.55 and Levels to 8. This will create large blotches over the surface of the object it is assigned to. Back up in the Watermark Mix map, add a new Noise map to the Colour 1 slot and label it “Diffuse Colours”
Enlarge Screenshot In this new noise map, set the Noise Type to Fractal, the Size to 40 and the Levels to 10. Set Colour 1 to RGB 160,80,65. Drag and drop this colour into the Colour 2 slot and amend it’s colour slightly so it’s just every so slightly lighter. This helps break up the surface a little.
Enlarge Screenshot Back up in the Watermark Mix map, add an Output map to the Colour 2 slot and label it “Watermark”. Instance copy the Diffuse Colours noise map into the Output’s Map slot and amend the Output map’s RGB level setting to 0.9 to darken the Noise map a little to create the watermark shade.
Enlarge Screenshot Back up at the top level of the material, drop in a Falloff map in the Self-Illumination slot and label it “Edge Sheen”. Set the Falloff Type to Shadow/Light. Drop in another Falloff map in the Light slot and label it “Perpendicular”.
Enlarge Screenshot At the top of the material, drop a Noise map in the Bump slot and label it “Noise Texture”. Set the Type to Fractal, Levels to 10 and Size to 0.2. Add a Splat map to the and label it “Faults 1”. Set the Size to 5, Iterations to 3 and Threshold to 0.15. Set the Colour 2 swatch to white (Continued in the Tips section...)
Enlarge Screenshot The final material setup rendered using Light Tracer and a standard directional light to simulate the sun. Depending on the scale of your objects you may need to tweak the map settings a little due to the mapping types used to get it looking right.
Download the max file! Zip file to accompany.

..::tips::..

Add a Splat map to the Colour 1 slot of the Faults 1 Splat map and label it Faults 2. This is to add some finer imperfections to the material. Set the Size to 3, leave the Iterations as 4 and set the Threshold to 0.15. To reduce the height of these additional imperfections, the colour strength isn’t that high, so set the Colour 1 to RGB 128,128,128 and Colour 2 to RGB 180,180,180. Finally, at the top of the material, set the Bump strength setting to 100 and assign the material to the pot in the scene.

If the pot has been situated outside for a substantial amount of time, or has been in an environment with a fair amount of moisture, mould will form around the sides (not necessarily the base) of the pot. This can be emulated by mixing two materials – our main ceramic material, and another “mould” material and use a noisy gradient to blend them together.

If the pot has been used, then you will find some internal staining of the surface caused by soil and other material. To create this, create an additional debris material and blend the two materials together using a noise map similar to using a gradient with the mildew. This time, select the internal polygons of the pot and assign the blended materials so this material setup is only applied to the inside of the pot. If the dirt uses new mapping, then the original ceramic material should still have it’s original mapping, therefore should blend together with the external polys without any problems.

Other fired ceramics can be created in the same fashion. Now you have covered the process to create terracotta, try tweaking the material to create fired clay by amending the diffuse colours to a lighter and slightly more yellow shade. Depending if the object was hand-made, adjust or include any modelling and/or material deformations to give this impression.

Initially published: 3D World magazine, Issue 45, December 2003.

Copyright Pete Draper, December 2003. Reproduction without permission prohibited.

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