Create a new page (We have used following settings but you can use your own)

Double click on Background layer & unlock it. Set foreground color to Black & background Color to White.

Go to Filter - Render - Clouds (Keep background layer selected)

Got to Channel Palette & create a new channel (it will be named to Alpha 1 automatically)

Keeping Alpha channel selected go to Filter-Render-Difference Clouds

Press Ctrl+F to apply last filter again.

Now select the RGB channel again & go to layer palette.

Go to Filter-Render-Lighting Effects.

Apply Lighting Effect with following settings.

You will get something like this.

Go to Image-Adjustments-Hue/Saturation & use the following settings to colorize it.

Use Burn & Dodge tools to make it some more realistic.