Materials Exposed to the Elements

Dear Readers,

Everything is susceptible to the forces of nature. In time, even the hardest rocks will be ground to dust. However, in archeological time scales rocks are usually preserved quite well. The site of Fort St. Joseph is located in a floodplain area, so the soil is generally saturated with water. You might think this is a bad thing, but it actually means the soil is an anaerobic environment, like a swamp. This prevents harmful microbes from growing. The cyclical flooding and draining of the site kind of washes the dirt, preventing it from becoming acidic. Stone and ceramic pieces haven't really had a reaction due to the water, however, some materials have and the chemical reaction can have drastic effects on an artifact. To learn more about this, I wanted to research how to identify these objects and see the true history hidden beneath the patina.

A piece of copper wire and two pieces
of scrap found at Fort St. Joseph.

Copper 

If you’ve ever seen an old penny or the Statue of Liberty, you know what to look out for. Copper + oxygen creates copper oxide. Copper artifacts can be identified by their bluish-green patina. Brass and bronze also have the same patina, as they both contain copper. In this picture, we have a thicker piece of copper wire perhaps part of a handle to a copper kettle and two copper flakes. The copper flakes have varying levels of patina, but the wire has none.

A musket ball that was fired and hit an
object with enough force to impact its shape.

Lead

Lead has a grey patina. Those new to the field may mistake lead shot for pebbles, and impacted musket balls can sometimes look like weird rocks. However, any lead artifact can be identified by its density. To test, drop one into the palm of your hand from a few inches above. Even a 5mm diameter lead pellet will feel unusually heavy for their size.

An iron fishhook that has had
some larger pieces of rust removed. 

Iron

Of all these materials, iron is the most susceptible to oxidization. After 300 years in the moist earth, something like a square-cut nail may look like nothing more than an amorphous reddish-brown blob. They may look a lot like concretions (iron-rich solid masses in soil) so a magnet is sometimes useful to distinguish an iron artifact from an extra-hard concretion. Metals will also continue to oxidize after excavation, so it’s important to store metal artifacts in a moisture-free climate.

Glass

Glass has the most interesting patination of all the materials recovered from the site. Certain glass types may patinate, as the moist condition at the fort allows minerals in the soil to bond with impurities in the glass. The color and texture of patination is not consistent, but it’s generally a tan grey color and has a texture like soft flakey sandpaper (below). To me, it seems that more of the green bottle glass (left) can be patinated rather than the blue-green glass found at Fort St. Joseph. 

Another interesting effect of weathering on glass is iridescence (below). Iridescence is the result of the same processes as patination, however, instead of minerals in the soil bonding to the glass, the impurities in the glass leech into the soil, causing microscoping flakes of glass to break off, creating a complex geometry that causes a prism effect, resulting in a beautiful oil-spill-rainbow effect on the glass. It’s not unusual for glass artifacts to have both patina and iridescence.

Conclusion

It’s important to note that weathering processes do not stop once an artifact is excavated. If stored improperly, metal will rust or tarnish. Wood, paper and bone are attacked by mold and microbes. They are also subjected not just to the forces of nature, but can also be impacted by humans and the curation crisis. Improper storage puts an artifact’s context and history at risk as the artifact itself can be damaged and/or lost. Proper curation requires climate control, security, cataloging, and regular maintenance which is expensive. The cause of this curation crisis is not just a lack of funding, but also a lack of personnel.

Hopefully this blog has enlightened you to the importance of curation, and if you’re interested, maybe consider a career in conservation, museum studies, or cultural resource management.

- Evin