During the development of the scene and this tutorial, a terrorism activity happened in Madrid, the city where I was born and where I still live. More than two hundred people died, and more than one thousand people have been wounded. Please permit me now remember all of them. I wish art save us all someday.
This scene has been completely done with the textures of the 3DTotal collection. More so, with the textures of 3D Total's last delivery, Total Textures v5 Dirt & Graffiti, where you can find some very useful dirt maps.
The first thing that you have to consider when you are going to make an architectural scene (or another kind of image) is to get the best references. Best of all is that in this case the references have already been done for you by 3DTotal. With this idea, I don't want to invite you to take pictures of walls to get textures (all the textures made for this tutorial was made from clean maps). Contrarily, you have to observe how walls get dirty, how time affects to the rock, the concrete and the bricks. How the different materials react with the light. Also, you can go into the street to look for some buildings that could inspire you, or that help you make good compositions (to make a good scene something essential is the location of the camera). Very important too, is that you take note of how the light draws the shadows. You have to consider the light as one of the most important element of your scenes.
I rarely know how the scene is going to turn out. Think it's very important to improvise above all when I'm lighting or composing. I usually have very clear idea of what I want to reflect or what kind of ambient I want to obtain. However, how it will turn out is always a mystery.
How to use the dirt maps
This is the fun part.
In photoshop use the multiply, overlay layer etc styles... - Control the mixture with the opacity setting of each layer.
Using color range selection - Select the black or white tones of the dirty map that you consider interesting and bring that selection to your clean map, paint over it. Then, as before experiment by changing the layer styles.
Select the black or white tone of the dirt map. Create a new layer over the clean map, and paint with any colour you want and experiment with the layer style.
Again using the selection from above use it on another texture and cut out the parts that interest you with the mask selection. Again layer these parts of the selected texture over your clean map and try to change the layer style as before.
If it is necessary you can always apply a feather to the selection to avoid cutter lines.
Select the black or white tone of the dirt map. Bring selection to another texture and cut the part you want. Paste the selection over your clean map and experiment with the layer styles.
Or use black and white map as mask between two materials
When you want to apply two kinds of material with different over a wall surface for example, you could use a blend material and a dirty map to mix them naturally.
Don't forget that you can also mix the above ways of using a dirt map. Try to experiment with them and try to create your own ways to use them.
I hope that this tutorial has helped you any way.
Thanks all of you,