Square Nail Corrosion Mystery

[Appalachianman76]

I've been hunting a Civil War camp over the last month and have discovered a mystery in how some of the square nails have corroded. 99.9% of them show the normal corrosion of heavy rust to the point of "popcorning" (developing large incrustations with the surrounding soil and minerals) and even dissolving away. However, I've found three square nails from the same depth and time period that show little or no corrosion at all. They're almost like new! What's really weird is that half of the nail on the far right rusted away while the top half remained in great condition. I've posted a picture below showing the normal examples and the abnormal ones. All the nails have been cleaned by washing in hot soapy water with a toothbrush to get the dirt off (No electrolysis). These came from heavy clay soil on the top of a hill with no water around. Does anybody have a good explanation on how this can happen? How can a nail that is 150 years old not rust? Thanks for the thoughts.

 

Amazon Forum Fav 👍

Agony and Death on a Gold Rush Steamer: The Disastrous Sinking of the Side-Wheeler Yankee Blade - Grab it through Amazon!

[Clay Diggins]

I live in the Southwest and most nails we find are not rusted. Without moisture - no rust. Consider that your site may have been partially covered by a building or shelter of some kind.

Another possibility is that the nails are modern. Square, cut and rose head nails are all still made today. Maybe a friendly humorous detectorist left a mystery for you?

 

[BosnMate]

I have the same question. I hunted the site of an long missing cabin on a homestead in SW Oregon. Someone must have tipped over a can or bucket of square nails, because in one tight local spot, there was a bunch of nails, so many I quit using the detector and screened them. Some were encrusted with rust, and others were hardly rusty at all, and all came from the same hole. The photo is the nails as found. I also found an Indian Head penny, forget what the date was, somewhere around 1900, so the nails were probably in the ground for more than 80 years. There were no wire nails found at the site. Anyhow, you would expect them to be very rusty, and they weren't.

 

[villagenut]

There may be different types of iron content in nails which allow some to be more corrosive resistant, such as hand wrought nails compared to the later cut nail. Also too, there is possibility that nails that have been in rotting timbers in the ground or from a building burned, may have years of protection before totally exposed to ground effects.

 

[Appalachianman76]

There may be different types of iron content in nails which allow some to be more corrosive resistant, such as hand wrought nails compared to the later cut nail. Also too, there is possibility that nails that have been in rotting timbers in the ground or from a building burned, may have years of protection before totally exposed to ground effects.

I hadn't thought about the different iron content. Makes more sense though. We get a lot of rain here in Kentucky. A nail starts to rust in a matter of days if it is left out. I found a strip of nails from a nail gun were the owner built his house in the 1990's. They where rusted and fused so bad I could barely recognize them. The area had been open and used during the 1800's but abandoned and left to grow up into forest by the 1940's.

 

[redbeardrelics]

Perhaps the non-rusted nails were for some purpose oil impregnated, and that provided some protection from ground moisture. Maybe similar in effect to the "seasoning" that is done on cast iron frying pans?

 

[1320]

There may be different types of iron content in nails which allow some to be more corrosive resistant, such as hand wrought nails compared to the later cut nail. Also too, there is possibility that nails that have been in rotting timbers in the ground or from a building burned, may have years of protection before totally exposed to ground effects.

^This

 

[Clay Diggins]

If you consider that rust is a chemical process you will see that a simple change of acidity in soil can have a huge effect on the rate that iron rusts.

Rust is the natural state of iron (ferrous oxide). Rust occurs when an exposed area of a ferrous (iron-containing) alloy (like steel) drops below a pH of about 8.2 or 8.3.

Alkaline soils have high pH (above 7.5). Clay soils in combination with most forms of salt can cause an alkaline soil usually in the form of carbonate or caliche. High alkaline soil = no rust.

All rusting requires the presence of water. Even low pH soils that are dry prevent rusting. High pH or no moisture = no rust. If you are seeing rust in one are and no rust in an adjacent area one or both of these factors are the reason.

 

[Appalachianman76]

If you consider that rust is a chemical process you will see that a simple change of acidity in soil can have a huge effect on the rate that iron rusts.

Rust is the natural state of iron (ferrous oxide). Rust occurs when an exposed area of a ferrous (iron-containing) alloy (like steel) drops below a pH of about 8.2 or 8.3.

Alkaline soils have high pH (above 7.5). Clay soils in combination with most forms of salt can cause an alkaline soil usually in the form of carbonate or caliche. High alkaline soil = no rust.

All rusting requires the presence of water. Even low pH soils that are dry prevent rusting. High pH or no moisture = no rust. If you are seeing rust in one are and no rust in an adjacent area one or both of these factors are the reason.

I never knew about the pH level having a effect on rust. We do have natural pockets of salts in the area. In fact there where salt works close by that were destroyed during the Civil War. Thanks for the great information!