The area around the National Capitol
This area includes the Capitol building, the Peace Monument, the Grant Memorial, and the Botanic Gardens. We begin the tour at the southeast corner of the Capitol, and go clockwise around the Capitol (along the south, west, and then north sides). We then follow a walkway heading west, from the northeast corner of the Capitol, to see the Peace Monument at the intersection of First Street and Pennsylvania Avenue, NW. We continue south along First Street to the Grant Memorial and then south again to the Botanic Gardens. Total distance is about one kilometer, or about three-quarters of a mile.
The Capitol Building—Site 1
The Capitol was built in stages; the cornerstone of the main building was laid in 1793, the north wing was completed in 1800, and the south wing was completed in 1807. Both wings were burned by the British in 1814. The capitol was then rebuilt, and it has been modified several times throughout the years. A major program of cleaning, replacement, and repair was begun in the late 1980’s. The center building of the Capitol is painted sandstone, but the north and south wings, housing the Senate and the House chambers, are marble. Around the Capitol we will observe various examples of dissolution and blackened alteration, especially on the marble balustrade that surrounds the south, west, and north sides of the building.
Beginning at the southeast corner of the building, by using binoculars we can see some areas of blackened alteration in the Corinthian column capitals. A more accessible example is found under the overhang of the large square ends of the marble balustrade at the southeast corner of the building. The black crust is made of gypsum plus dirt that accumulates in sheltered areas. No black crust is present along the cracks between the stones; rain water probably flows in these areas, dissolving the gypsum and preventing accumulation of a crust. Not all black areas on this baluster are gypsum; in some places near the bushes, you can see greenish-black moss growing on the stone. The top surfaces of the marble balustrade are coarse and rough, because of dissolution between grains, compared to areas that are protected from running or washing water where the black alteration crust forms.
The United States Capitol building.
Blackened alteration has accumulated under the overhanging edge of this marble balustrade corner. Southeast corner, U.S. Capitol Building.
Pock marks in marble columns, south side of U.S. Capitol building. Silicate mineral inclusions in the marble loosen and fall out when the calcite around them is dissolved by acid rain.
Another dissolution feature of marble is the pock-mark effect on the square bases of the building columns. Silicate mineral inclusions in the marble were loosened by the dissolution of the surrounding calcite, causing the inclusions to fall out of the stone. A particularly good example of this is found on the fourth column west from the southeast corner of the Capitol building. The pock-mark dissolution is also found at several other places on the building.
The marble balustrade on the west side of the Capitol building shows both dissolution and alteration.
A recently replaced marble baluster at the Capitol has edges that are only beginning to round.
Black alteration crusts under the west balustrade of the Capitol have begun to spall (peel) off, revealing crumbling white marble underneath.
We will follow the marble balustrade around the building, noting differences in deterioration. Some parts of the balustrade have obviously been replaced, thus enabling us to observe various stages in the stone deterioration. The edges of the balusters are sharp when new and become rounded as they age. Blackened alteration crusts have accumulated on the sheltered sides of the balusters and under the overhanging top of the balustrade. In some spots under the rail the blackened crust has spalled off, exposing fresh surfaces and more vulnerable stone. Some carvings on the balustrade corners are worn, whereas others have blackened alteration; this difference in weathering may be due to local effects of wind and rain. Along the steps leading to the terrace on the west side of the Capitol, gypsum has accumulated on large areas of the wall. Gypsum can accumulate on any surface that is not washed by water.
As you walk north along the west side of the Capitol, look at the central part of the building. The walls here are painted sandstone. Despite recent restoration of the building, you can see evidence of past stone deterioration, including the accentuated lines from bedding in the stone and the pock marks where rounded inclusions have disappeared. We will see an example of this same sandstone that is not painted in the buildings near 17th Street.
At the northeast corner of the Capitol building, the marble balustrade ends in square blocks like the ones we first examined. Here you can see an example of preferential dissolution where the silicate mineral inclusions remain and the calcite around them has been dissolved away. Also, on the north side of this block, examine the blackened grains on the top surface with a hand lens. Not all of the black material you see on stone is gypsum; some is of biological origin, probably algae or a fungus.
A marble block that forms the northeast corner of the Capitol balustrade shows preferential erosion of the calcite around a silicate mineral inclusion.
To continue the tour, follow the pathway that heads west along the north side of the Capitol, towards First Street. As you approach First Street you will see a sandstone, diabase (a dark igneous rock), and granite fence with various carvings. Because these stone types are resistant to acid attack, the carvings show little damage.
The Peace Monument—Site 2
The Peace Monument, dedicated in 1878, is made of Italian marble.
This monument, dedicated in 1878, is made of marble from Carrara, Italy. The statue does not show much damage, but if you look closely, you can see alteration crusts (some are light orange) in protected places and graininess and roughness in places that are exposed to rain. Carved statues present varied surfaces that direct rain washing and runoff.
MAP OF WASHINGTON
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Sites on the tour: 1. THE CAPITOL BUILDING 2. THE PEACE MONUMENT 3. THE GRANT MEMORIAL 4. BOTANIC GARDENS BUILDING 5. JEFFERSON MEMORIAL 6. LINCOLN MEMORIAL 7. CAPITOL GATEHOUSE 8. ORGANIZATION OF AMERICAN STATES BUILDING 9. DAR—CONSTITUTION HALL 10. DAR—MEMORIAL CONTINENTAL HALL 11. CORCORAN BUILDING 12. RENWICK GALLERY 13. FEDERAL TRIANGLE BUILDINGS 14. WASHINGTON MONUMENT
Continue south along First Street to the Grant Memorial on your right.
The Grant Memorial—Site 3
The Grant Memorial consists of bronze statues on marble bases; although the statues were cleaned, the staining on the marble remains.
This memorial, dedicated in 1922, consists of a group of bronze sculptures mounted on marble bases. Bronze weathers outdoors if it is not cleaned and waxed regularly. Like stone, bronze dissolves where it is exposed to rainfall, developing a green color and a pitted surface, and it also alters in sheltered areas, with accumulation of a blackened layer. The most notable stone deterioration visible here is the green stain on the marble bases, caused by runoff from the weathered bronze. The green stain does not damage the marble, but it is unattractive, and there are no methods currently available to remove the stain without damaging the marble.
The light-green color on the bronze statues at the Grant Memorial is typical of the way bronze weathers when it is exposed to acidic rain; the rain dissolves some of the metal and causes staining of the white marble bases.
Continue south, crossing Maryland Avenue, to the Botanic Gardens.
Botanic Gardens Building—Site 4
The Botanic Gardens building is made of limestone.
This limestone building was built in 1931. Like many of the limestone buildings in Washington, this building has been cleaned, so it does not have an accumulation of surface dirt. However, the cleaning and regular washing by rainfall have accentuated the fossils in the stone, which dissolve less readily than the calcite matrix. Some of the sculpted heads above the arches of the building show small black crusts. On the east side of the building, microorganisms naturally present in the stone contribute to the deterioration (blackening) of the stone, where water drips from a joint in the roof.
Fossil details stand out on the limestone at the Botanic Gardens building; the fossils are more resistant to dissolution than the calcite matrix that holds the fragments together.
The Botanic Gardens Building is the last stop in the Capitol area of the tour; you may wish, however, to see some bronze alteration on the Garfield Memorial (First St. and Maryland Ave.) and the accentuated fossils with surrounding algae or fungi on the limestone posts near the Capitol Reflecting Pool. The next stop, the Jefferson Memorial, is about 3.5 kilometers (2.2 miles) from the Capitol.
Jefferson Memorial—Site 5
The Jefferson Memorial is made of marble and was dedicated in 1943.
The Jefferson Memorial is a marble building, dedicated in 1943. One of the most striking deterioration features to observe here is the loss of silicate mineral inclusions in the marble columns because of dissolution of the calcite matrix. Close examination of the grooves shows flakes of mica and sometimes grains of pyrite. Blackened crusts are visible on the column capitals that are sheltered from rain and from regular washing of the monument.
Several of the column shafts at the Jefferson Memorial have grooves that follow the inclusion traces in the marble, where the mineral inclusions have weathered out and been lost.
A close look at some of the weathered grooves in the columns shows that small bits of mica and pyrite remain.
The National Park Service began a survey of the condition of this memorial and the Lincoln Memorial in 1992. The results will be used to help make decisions on treatment, cleaning, and preservation. The information gathered from the survey will serve as a known baseline for the condition of the stone, so that future changes in the condition of the buildings can be assessed. In May 1990, a part of one of the column capitals (called a volute) broke off and fell onto the northwest portico. This failure raised concern about all the volutes at the Memorial, so several other cracked volutes were removed, and studies are being conducted to determine why they cracked. Because of where and how the volute broke, it is unlikely that acid rain or air pollution contributed to the failure. The broken pieces will probably be replaced, but only when the reason for their failure is understood, so that an appropriate replacement technique can be chosen.
Part of one of the column capitals at the Jefferson Memorial broke off and fell onto the portico in 1990.
The next stop is the Lincoln Memorial, 1.8 kilometers (a little more than a mile) northeast of the Jefferson Memorial.
Lincoln Memorial—Site 6
The Lincoln Memorial, dedicated in 1922, is made of marble from Colorado. This building has few alteration crusts, in part because it receives regular cleaning and in part because of the design of the building. Except for the features around the entablature (the edge of the roof), there are few sheltered areas where alteration crusts can accumulate. With the aid of binoculars, you can see some alteration crusts along the underside of the roof overhang; in these places the marble is very badly crumbled under the alteration crusts. Some columns show preferential weathering or loss of inclusions, but some of this damage might be from graffiti removal. The most visible dissolution feature is sugaring, where the stone has lost its polish and the surface now feels rough. Visitors have affected this popular memorial too; several of the columns, especially the limestone columns inside the chamber, show darkening and rounding of edges where visitors have touched them over the years.
One interesting feature at the Lincoln Memorial is differences in stone condition that must come from variations in the stone. At several places around the outside of the memorial, adjacent blocks of marble show very different surface roughness. Since the blocks of stone have the same orientation with respect to wind, rain, and pollution, the difference in condition cannot be due to exposure and must be related to basic characteristics in the stone that was used.
The Lincoln Memorial is made of marble and was dedicated in 1922.
Under the roof overhang is one of the few places at the Lincoln Memorial where alteration crusts have developed on the marble.
Some columns at the Lincoln Memorial have flattened chalky areas where inclusions have weathered differently from the surrounding calcite.
The marble guttae on the roof overhang are crumbling and falling apart underneath blackened alteration crusts.