The Lorton Reformatory is well-known to locals as a brickmaking center in southern Fairfax County. From 1912 to 1967, Lorton Reformatory produced tens of millions of distinctive red bricks for the Lorton Prison and other buildings. By 1929, 6+ million bricks were produced annually. Brick making benefited from labor of the prisoners, the reduced cost of producing bricks locally for the Lorton penitentiary, and proximity to the Potomac to export bricks to Washington, DC. In this Earthcache, we're going to learn about an often-overlooked reason - the availability of the clay and sand that make up bricks! Let's get started.
Bricks are made through a series of steps:
- 1) Quarrying of clay and sand
- 2) Weathering of the raw ingredients
- 3) Shaping the bricks
- 4) Drying the bricks
- 5) Firing the bricks
In this Earthcache, we visit two locations that illustrate these steps in reverse order. A few notes: Permission for this cache has been generously granted by the Fairfax County Park Authority. We appreciate their support of our hobby. NO NIGHT CACHING IS ALLOWED. There is no need to leave the paved path or bridge to finish this Earthcache, although you can get closer to the object of interest at Stage 2 using the optional reference points given.
Stage 1 is the historic brick barrel arch bridge at the posted coordinates. Built in 1946 by prisoners with bricks made at the Lorton Reformatory. Let's take a closer look at the bricks and how they were made.
Firing the bricks - Firing bricks at ~1800-2400°F has three major effects. First, firing vitrifies the bricks, forming a melted, glassy layer on the brick surface. Different brick types (interior construction vs. exterior sidewalk) may be fired at different temperatures and have different amounts of vitrification. Second, firing oxidizes FeO to Fe2O3, producing the distinctive red color. Finally, firing decreases moisture in the brick. Bricks lose 10-15 weight % from shaping to firing.
Question set 1: Look at and touch the bricks at the base of the bridge.
- Do they all feel the same (smooth and glassy, rough and coarse) or do they feel different?
- Do you think these bricks all experienced the same degree of vitirification? Why or why not?
Drying the bricks and shaping the bricks - Sun-drying of bricks allows much of the water to evaporate naturally. If all that water was lost during firing, the bricks crack and break. Much of that water is bound within the clays, which is remarkable since clay makes up only about 1/3 of the mix for a typical brick. The rest is sand or larger particles of rock.
Question set 2: Standing in the barrel bridge and looking to the SE, you will find several bricks whose faces have broken off, exposing the interior of the bricks. These are about at head height for an adult. Take a careful look.
- What color is the interior of the brick?
- Are particles in the interior of the bricks sand-sized or larger pieces of rock?
- If larger rock pieces were included, do you think that changed the strength of these particular bricks?
Stage 2 is the center of the bridge over Giles Run. Here we'll think about the raw materials for the bricks. The clay and sand for the Lorton bricks was dredged from the Occoquan. The river naturally carried away any salts deposited, which are normally removed before brick making by weathering of the raw material. The source of the sand and clays in the Occoquan is the surrounding hills. The Potomac formation (familiar to some of you from GC94P7G) is rich in clays, particularly those that contain abundant water in their structure, and sand. It formed + million years ago when freshwater streams meandered along the coastal plain. It is common in SE Fairfax County.
Question set 3: Standing in the center of the bridge at Stage 2, look ~150°SE and down to the edge of the stream. On the bend of the stream, you'll see near-vertical exposures of lighter colored layers free of vegetation.
- What color(s) are the lighter colored layers?
- If they differ from the color of the bricks, why do you think that is? [Hint: The answer is in the writeup for Stage 1]
Extra credit (1.5/3 D/T) [and a few extra precautionary attributes for those making the side trip]
For those who would like to get a closer look at these layers, a side trail at the waypoint given leads to the deposit on the stream's edge. Do not attempt during high water. At the deposit, try taking a small piece of the different color layers and compress them between your fingers. Most of us have worked with clay at some point. Which color is richer in clay and which color is richer in sand?
Logging requirements
After reading the information above, send answers to the three sets of questions to the cache owner:
Question set 1: Look at and touch the bricks at the base of the bridge.
- Do they all feel the same (smooth and glassy, rough and coarse) or do they feel different?
- Do you think these bricks all experienced the same degree of vitirification? Why or why not?
Question set 2: Standing in the arch of the barrel bridge and facing SE, you will find several bricks whose faces have broken off, exposing the interior of the bricks. These are about at head height for an adult. Take a careful look.
- What color is the interior of the brick?
- Are particles in the interior of the bricks sand-sized or larger pieces of rock?
- If larger rock pieces were included, do you think that changed the strength of these particular bricks?
Question set 3: Standing in the center of the bridge at Stage 2, look ~150°SE and down to the edge of the stream. On the bend of the stream, you'll see near-vertical exposures of lighter colored layers free of vegetation.
- What color(s) are the lighter colored layers?
- If they differ from the color of the bricks, why do you think that is? [Hint: The answer is in the writeup for Stage 1]
WITH YOUR LOG, POST A PHOTO ON THE BRIDGE AT STAGE 2. Posting a photo that readily indicates that you (and anyone else logging the find) were at the location. You do not have to show your face, but the photo should include either you or an item with your caching name. Please do not show any answers to any of the questions above. NOTE: Per newly published Earthcache regulations, this is required to claim the find.
If responses to the questions above are not received in a reasonable time period, cachers will receive a request for answers. Failure to respond may result in deletion of your log.
Best Other (Wherigo, Earthcache)