A taxonomy of material appearance, Material Codes (from now on referred to as MCodes) are used to drive the rendering parameters of different rendering engines, based on physical properties.

The taxonomy is structured along 4 attributes, called taxons:

1. Group

2. Type 

3. Finish

4. Coating

Each attribute contains a set of agreed upon keywords such as wood, metal, etc. for group or raw, satin, glossy, etc. for coating.

Group Taxon

The first attribute is the Group. We have split materials based on their physical properties, composition and origin.

If you are looking for common or suggestions of mcode go to Common Mcodes.

Type Taxon

This property is a textual description of a material type within a group. It varies depending on the Group choice.
Types of Metal include Chrome and StainlessSteel, for instance.

This property will depend on the selected group; the groups do not necessarily have the same type.

Finish Taxon

This property is a textual description of the surface roughness. At a micro level, you can illustrate the scattering of light rays based on the roughness of the surface.

This property will depend on the selected group; the groups do not necessarily have the same finish.

Coating Taxon

Several materials are produced by coating a base material with a transparent or semi-transparent coating.
This produces a very characteristic look which is the combination of the coating material with its own reflectance pattern combined with the reflectance pattern of the base material.
The final reflectance is a more complex one than either of the two materials.

This property will depend on the selected group; the groups do not necessarily have the same coating.

The Taxonomy (per Group)

Metal

For certain metals with known reflectance properties, supplying texture color is unnecessary. Using their physical properties yields more accurate rendering. If color or textures are provided, the renderer should use them.

Appliance panel metals are never coated. Some noble metals like brass and gold are sometimes simulated with tin or aluminum plus a tinted coating. Painted metals should use Paint as their MCode, not Metal.

Type lists different metals because catalog provided colors or textures are unreliable in those cases.
Finish and Coating are listed from "roughest" to "smoothest".

Wood

Woods are classified as Hard or Soft wood, which affects the finish appearance.
The wood species mainly differ in texture, not direction. For example, maple is a hard wood with a maple texture.
If wood is painted, its MCode should be “Paint” instead of “Wood.”

Finish and Coating are listed from "roughest" to "smoothest".

Paint

Paint it’s classified by substrate, which affects its appearance.
Paint does not have coating specifications; the coating is part of the paint finish.
Flat paints appear uncoated, while eggshell to glossy paints look like the base with a rough to smooth coating. Finish ranges from "roughest" to "smoothest".

Mineral

For textured ceramic tiles imitating materials like marble or terracotta, the type should be “Ceramic” since the actual reflectance is from the ceramic base, not the imitated material’s texture.

Finish and Coating are listed from "roughest" to "smoothest".

Plastic

Plastics are composed of colored pigments suspended in a transparent polymer substrate. There can be a good dose of diffuse subsurface scattering in the plastic base material and the transparent substrate has the appearance of a coating. They are always coated so to speak so the coating does not have to be specified.

Finish is listed from "roughest" to "smoothest".

Solid Surface

Solid surface materials are engineered for use in countertops, sinks, and architectural surfaces. They consist of a natural mineral filler and a resin binder, plus additives. These components are combined, then cast or sprayed and cured into sheets or shapes.

Finish is listed from "roughest" to "smoothest".

Laminate

Common laminates feature color-printed paper covered by a clear plastic sheet. They are widely used in furniture, cabinets, countertops, and wall panels. The decorative layer mimics materials like wood, stone, or metal, available in various colors and textures.
Types are classified by the visible layer beneath the clear plastic, which defines the laminate's look. The surface is smooth with a Glossy or Matte Finish. Laminates have no separate Coating properties, as all are covered by a protective plastic layer.

Finish is listed from "roughest" to "smoothest".

Fabric

Fabrics are classified by fiber type, which mainly determines their appearance. For example, wool is rougher, while rayon is smoother.

Fabrics have no coating entries since they aren't coated. nSome synthetic fibers are naturally coated, but the weaving technique mostly affects the look.

Leather

Dressed or tanned hide of an animal, usually with the hair removed.

Carpet

Thick heavy covering for a floor, usually made of woven wool or synthetic fibers.

Wallpaper

Wallpapers are not all made of paper. Some of the more expensive wallpapers are made of fabrics. The vast majority of wallpapers are not coated. Vinyl wallpapers have a plastic appearance. And the appearance is mainly influenced by the actual material type

Glass

Glass is a hard, brittle, translucent or transparent material, often white or colored, made by fusing sand or silica with lime, potash, soda, or lead oxide, and has a conchoidal fracture. It's used for windows, tableware, lenses, and decorative items.

The Glass MCode defines only the glass surface appearance, not how it transmits light. Glass both transmits and absorbs light. For example, red wine bottles absorb much of the red spectrum but less of yellow, green, and blue, giving them a greenish look. This absorption effect isn't included in MCode and must be added via the baseColorFactor.

Emitter

A material that Emits light. Used to define light sources for rendering purposes. An example could be a lit TV screen, light bulb, or neon sign. Not only would they not be affected by scene lighting, but they would also emit light.

Miscellaneous

Odd materials that couldn’t be placed in the above list (ex: food and drinks, flora, animals, human skin, etc.) Also used to flag certain materials as Invisible or Undefined for rendering purposes.

Common Mcodes

Here are some common MCodes.