Need to make (node setup) of realistic dirt/ grime/grunge on top of image texture of ceramic tiles

Question

I've already created a node setup with bump mapping and gloss, but I have no idea how to add or combine an image or texture to create a realistic dirty/worn look on the clean tiles.
I tried the tutorial http://www.blenderguru.com/tutorials/how-to-grunge/ , and I can bake the image but I am not sure how I would combined them to give the desired effect.

The image I wish to improve on or change (add dirt to) can be found here. http://www.cgtextures.com/texview.php?id=65010&PHPSESSID=rklgncit37atdpanj155e3jvg5

Any advice would really help me out! Thanks

Answer 1

Adding convincing dirt and grunge to any model requires multiple layers of shaders. I usually use three main layers, surface dirt, crevice dirt, and dust.

Surface Dirt:

Surface dirt is just smudges and such that accumulates across the surface of an object. To create this just mix your normal shader for your material with a dirty shader using a grunge texture for the mix factor.

Note: Make sure the image texture you are using for a mask is set to non-color data.

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Crevice grunge:

Usually grunge doesn't accumulate evenly over an entire object, it likes to get caught and pile up in corners and crevices where it isn't easily brushed or blown away. To simulate this in Blender I will be using the brand-new pointiness input from the input > geometry node (so make sure you are using Blender 2.74 or later). You usually have to tweak it's output with a color ramp to get some better contrast, then just add it to the grunge mask you are already using.

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Dust:

Dust usually doesn't stick to an object very much, it just settles on the top. To get this effect I plug the normal output of a geometry node into a Seperate XYZ node, the Z output of this node will give how much the face is pointing upwards. Just use this output, multiplied by another grunge texture, as a mix factor for the dust shader.

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Here's the final result:

Answer 2

There are two types of dirt masks you should consider for this type of a surface. Firstly the dirt that accumulates in the crevices of the surface, in this case the grout lines, and secondly surface dirt/tarnishing.

I've set up a nodetree demonstrating one method of creating both these effects here:

And here is a progression gif showing the stages of the effects:

In addition, the noise and masks are generated with procedural textures not image textures, which can be beneficial in many circumstances, particularly when it comes to tiling issues across large surfaces.