This effect was generated in Filter Forge, a Photoshop plugin that allows you to create your own filters.
This filter generates a rust texture with transparent areas. The rust is concentrated in the darker areas of the source image, the lighter areas are transparent. Use the Noise / Image slider to adjust how strongly the source image influences the distribution of rust areas.
rust, stains, metal, iron, steel, old, worn, corrosion, corroded
This filter has earned its author one of our rewards. They are given to the authors of popular filters and include a free copy of Filter Forge.