Cast iron pitting, what causes it?

[Ray Emerson]

I have seem multiple exaples of cast iron pitting.  What causes it in an old piece like this:


Much of the rest of the waffle iron looks so pristine, I didn't understand why these areas looked so bad.

Thanks!

Ray

[Ron_Wheeler]

Usually rust from moisture or an acidic solution left on the surface would be my guess on the waffle iron.  You'll also see pitting on the bottom side of a lot of skillets that problably was caused by exposure to extended open flames from the old wood and coal stoves.  It was common in those days to remove the 'eye lid' and place the skillet in the hole to get more direct heat.

[Jesse and Kim Dunfee]

Agree with Ron. Thats some nasty pitting there. Something sit on them for a very long time and ate the iron.......

[Jeff Seago]

This pitting is kind of weird, where it is at anyway.  Last time I saw pitting that occurred in a place that I considered odd was on an old international 566.  We pulled it out of the shed and the mice had overran the engine compartment.  There were spots of pitting like this on the frame where the nests were.  Can you guess what might have cased them???

I am not suggesting that this is what happened to this piece, just to clarify.  I am only saying that pitting this deep in these areas seems strange to me.

[Ray Emerson]

We pulled it out of the shed and the mice had overran the engine compartment.  There were spots of pitting like this on the frame where the nests were.  Can you guess what might have cased them???

I suspect urine from the mice.

Ray

[Roy G. Meadows]

Harold,
Much of the severe pitting on items such as your waffle iron occurred in the early 20th century and was caused by sulfur in the natural gas. This gas was often called "town gas". In those days the naturally occurring sulfur compounds were not removed from natural gas as they are today. Direct impingement of the flame containing sulfur compounds on the cast iron would result in the reaction of the iron and sulfur to form iron sulfide. This loss of iron would form deep pits in the cast iron. This is a simplistic explanation; the actual corrosion mechanism is more complicated.
This is not to infer that rust, accelerated by the presence of moisture or water or p___, did not cause corrosion. However, it is usually more general and less pitting in nature and occurs where moisture collected.
                                                                                       Roy Meadows