Rust pattern on carbon steel...

[galadduin]

I left a couple of stanley knives in the rain (not intentionally). Today I noticed the rust patine. It looks like a web, first rust begins from some points and expands in lines originated from that point. The path of the rust lines resembles the fractal geometry. When the lines connects to each other the lines grow wider and enlarges to circular pattern. Can an expert explain why the rust behaves like this... Here is a crappy photo about it...

 

[mete]

Fractal patina !! HA, HA ! Actually that photo shows rust, pitting .We wouldn't call that patina.Rust starts as pits. Where depends on various surface conditions - surface energy, scratches, oxide layer, contaminents such as oil etc.Once a pit starts you can even get galvanic corrosion between oxide layer and metal.

 

[galadduin]

Fractal patina !! HA, HA ! Actually that photo shows rust, pitting .We wouldn't call that patina.Rust starts as pits. Where depends on various surface conditions - surface energy, scratches, oxide layer, contaminents such as oil etc.Once a pit starts you can even get galvanic corrosion between oxide layer and metal.

Thanks mete, I was just asking why the rust begins from a point and grows. I wasn't identifying as a usable patina, but it looks like there is a growth behavior. Photo doesnt show enough details I know, and I know it is just an ordinary rust... I didn't notice before but under magnification the pits has some linear rust lines like spider web around at the beginning. I was asking are those small lines follow a crystalline structure boundaries or is a random spreading... It is not on topic, just out of curiosity....