Painting dirt using vertex painting
Written by: Julio Juárez

In this tutorial you will learn a very simple but effective way to add dirt to an object using the vertex paint tool. Take note that you can also use this method for applying rust to metals or for adding more detail to a texture.

 

1. First well start by creating a teapot and upping the segments to ‘6’ but feel free to use any other mesh if you want.
2. now well convert this object to an “editable poly” by right clicking->convert->editable poly

Note: you can use this method in all types of surfaces (nurbs, patches, poly’s and meshes)

3. now we will make a sub-object selection in order to choose witch parts of the object will be paint able (selected) and which parts will not (unselected), click on the polygon sub-object button and marquee select all the polygons of the teapot which will make them all paint able.

4. Now apply a “vertex paint” modifier to the object.
5. under the vertex paint parameters click on the ‘vert color’ toggle in order to display or disable our paint in the viewports, you can also use the illumination toggle to turn scene lights on or off, keep illumination ‘off’ and vert color ‘on’ for now.
6. now were ready to start painting, before we start ill explain that in this case we will only need to paint using black, gray and white colors what this will do is define the areas were the dirt will be visible, dark colors is were the dirt ‘will’ be visible and white/light colors is were it will ‘not’ be visible, with that in mind lets start painting. 
7. Click the paint vertex color button in order to activate the paint tool.

Note: to change a color just right click that specific color and pick another one in the color selector, it is up to you were you want to paint your dirt. Here’s a screen of my finished paint.

8. After you finished painting the object were ready to use this information in the material editor in order to add the dirt to our material, press the ‘M’ key on your keyboard to open the material editor.
9. we will use a “blend” type material in this case in order to separate our dirt material from our base material, so click on an empty material slot, then click on the material type button (the button that says standard by default), from the material map browser window select ‘blend” and click ‘ok’.

Note: It will ask you if you want to discard old material or keep the old material as sub-material, just select discard.

10. Now what will make the dirt material in the ‘material 1’ slot, expand the material 1 slot.
11. scroll down and open the ‘maps’ rollout, we will use a noise map for our dirt color, click on the button next to ‘diffuse’ and pick ‘noise’ in the material map browser.
12. With the noise parameters expanded in the material editor, change the colors of the noise material, give one color a gray-brownish color tone and a lighter gray-brownish tone to the other, and make sure the colors have a low saturation /sat value in order for the dirt to be more on the gray side to make a more realistic dirt material.

Note: for the first color I used a color value of R:113 G:103 B:78 and used R:161 G:146 B:111 for the second color.

13. Change the noise type to ‘turbulence’, the size to ‘10’ and the ‘high’ threshold value to ‘0.5’ in order to give more detail to the dirt.

Note: feel free to add more detail to your noise material you can even use yet another smoke map or even a noise as one of your smoke colors and one for the other in order to make an even more detailed dirt material.

14. Click on the ‘go to parent’ button ‘twice’ in order to go to the root of our blend material, now click on the button next to the mask and assign ‘vertex color’ to it from the material/map browser. What this does is that it blends our dirt material with the base material (material 2) according to the color information in the vertex color map we painted.

Note: like stated on step 6, dark colors is were the dirt ‘will’ be visible and white/light colors is were it will ‘not’, so you can say that material 1 (our dirt material) is the black color and material 2 (base material) is the white color and the mask image blends the two together.

15. Were finished!, you can change the parameters in material 2 in order to get a more interesting base material but since this is a tutorial for making dirt we will live the base material as it currently is.

Note: this is not necessary but for testing purposes you can change the diffuse color for the material 2 to white in order to make the dirt a little more apparent especially if you plan on making further tweaks to it.

With that said just render your scene!.

 

Final note: you can use this method for making things such as metal rust or adding details or different maps to only certain painted areas, this is a very good method because it gives you allot of control over the final look of the dirt especially to more complex models because were using vertex coloring we don’t have to deal with unwrapping or dealing with uvm’s in order to add the materials to them, hope you got something out of the tutorial.

 

This tutorial was written by: Julio Juárez

Copyright © by Julio Juárez