In order to complete this EarthCache, please visit at least one of the 5 listed waypoints and take a photo of yourself in front of your favorite example of clay terracotta in downtown Aurora. Then send me the answers to the questions below.
*Please note, all of the listed waypoints are visible from the public sidewalks/roadways. You do not need to visit all 5 waypoints but these 5 buildings have good examples of terracotta architecture*
Terracotta generally will have an reddish-brown or orange/tan color. It is typically found above doorways and around windows. Some terracotta artworks are very intricate and detailed ornamental pieces.
Waypoint #1 - N 41° 45.452′ W 88° 18.950'
Waypoint #2 - N 41° 45.498′ W 88° 19.088′
Waypoint #3 - N 41° 45.426' W 88° 18.791'
Waypoint #4 - N 41° 45.455′ W 88° 18.963′
Waypoint # 5 - N 41° 45.569′ W 88° 19.376′
1) What is clay?
2) Natural clay can come in many colors. What are they?
3) Which type of clay is terracotta typically made from? Earthenware, Stoneware, or Porcelain?
4) Take a look at the terracotta architectural designs on the buildings. Do you see any examples of weathering? If so, describe what you see. Which type of weathering do you think may be responsible?
5) Post a picture of yourself (face not required) or a personal item in front of one of the listed waypoints. This photo should prove you physcially visited this EarthCache. You can also opt to email/message me the photo instead of including it with your log.
Historical Background
Founded in 1834, the City of Aurora emerged as a trading point along the Fox River, benefiting from its abundant natural resources, including fish, freshwater, limestone, and rich deposits of clay. This natural clay is one of the primary ingredients in "terracotta." While many people are familiar with terracotta as the orange-colored clay used for flower pots, its applications extend far beyond that. Terracotta has been utilized in architectural designs for thousands of years, dating back to around 26,000 BC and today, this versatile material can be seen through the architectural designs on several buildings of downtown Aurora. When you look at these examples of terracotta, remember that they began their lives as natural clay. There are 5 waypoints listed for this EarthCache but you do not need to visit all of them.
Understanding Clay
What is Clay?
Clay is a natural, earthy material composed primarily of fine-grained minerals, particularly phyllosilicates rich in aluminum and silicate. At first glance, it can easily be mistaken for mud. It is characterized by its soft plasticity when wet and its ability to harden upon drying or firing, making it valuable for a variety of applications. In its natural state, clay can appear in various colors, including white, gray, brown, tan, brick-red, orange-red, and even blue.
Formation of Clay
Clay forms through several geological processes:
- Weathering: The breakdown of rocks, particularly igneous and metamorphic types, through physical and chemical weathering. For example, feldspar decomposes into clay minerals like kaolinite.
- Erosion and Transport: Weathered particles are moved by water, wind, or ice, with rivers carrying these particles to calmer environments like lakes or floodplains.
- Deposition: As rivers slow, they lose energy and clay particles settle, forming sedimentary layers rich in clay.
- Compaction and Lithification: Over time, sediment accumulation on top of clay layers leads to compaction and potential lithification, turning sediments into solid rock.
Types of Clay
Different environmental conditions and parent materials give rise to various types of clay:
- Earthenware: Low-fired, porous clay used for pottery and architecture, typically reddish-brown or orange.
- Stoneware: Mid-fired, durable clay used for tableware and art, typically gray or tan.
- Porcelain: High-fired, white, and translucent clay used for fine china.
Uses of Clay
Clay has diverse applications across various fields:
- Construction: Used for bricks, tiles, and pottery.
- Art: Essential for sculptures and decorative items.
- Industrial: Found in ceramics, porcelain, and cosmetics.
- Environmental: Acts as a barrier in landfill liners and waste treatment.
Terracotta
Terracotta, meaning "baked earth," is a ceramic made from earthenware clay, typically unglazed and reddish-brown due to iron oxide content. Its common uses include:
- Pottery: Flower pots and vases.
- Building Materials: Roof tiles and bricks.
- Sculpture: Artistic pieces and ornamental elements.
Process of Creating Terracotta
The creation of terracotta involves several steps:
- Raw Material Preparation: Clay is extracted, purified, and mixed with water.
- Forming: Shaping using hand-building or wheel-throwing techniques.
- Drying: Air-drying to prevent cracking.
- Firing: The first firing (bisque firing) hardens the clay; a second firing may be needed for glazes.
- Glazing (optional): Enhances color and waterproofing, requiring a second firing.
Weathering of Clay and Terracotta
Weathering processes significantly affect clay and terracotta ornamentation, primarily through physical and chemical weathering.
1. Physical Weathering
This process involves the mechanical breakdown of materials without altering their chemical composition. Key factors include:
- Temperature Changes: Fluctuations can cause expansion and contraction, leading to cracks.
- Freeze-Thaw Cycles: Water infiltrates cracks, freezes, and expands, further damaging the structure.
- Wind and Abrasion: Particles can erode surfaces over time, especially in exposed areas.
2. Chemical Weathering
This involves chemical reactions that alter the material's composition:
- Hydration and Hydrolysis: Water can react with minerals in clay, causing it to swell and lose strength.
- Saline Weathering: Salts from the environment can crystallize in cracks, exerting pressure and leading to spalling.
- Acid Rain: Pollutants in rain can react with clay and terracotta, weakening the material and altering its color.
3. Biological Weathering
Although not a primary type, biological factors can contribute to weathering:
- Plant Roots: Roots can penetrate and expand cracks, exacerbating physical damage.
- Lichen and Moss Growth: These organisms can produce acids that chemically weather the surface.
Further Reading
For those interested in exploring the topic further, consider these resources:
- "Clay Minerals: A Physico-Chemical Approach" - Clay Minerals Society
- "The Geology of Clay" - U.S. Geological Survey
- "Understanding Terracotta and Its Uses" - Smithsonian Magazine