Design of the Second Bank Construction of the Second Bank History of the Second Bank Architectural Conservation of the Second Bank Related Links & Site Information Second Bank Home
Repair & Conservation History
Repair & Conservation Timetable
Material Characterization of Pennsylvania Blue Marble
Photographic Documentation
Overview of 1999 Conditions Survey
Glossary o f Masonry Conditions
AutoCAD Drawings of Recorded Conditions
Preliminary Observations & Analysis
Samples Taken & Materials Testing
Laser Scanning
Survey Recommendations
Report Bibliography
Acknowledgments
Exterior Treatments

 

1999 Conditions Assessment Survey of the Exterior Marble:
 ~~ Samples & Materials Testing

Portion of wall under north portico displaying the brown staining.
Portion of wall under north portico displaying the brown staining.

Limited analysis was conducted on the Pennsylvania marble from the north portico. Characterization included confirmation of the mineral content of the marble inclusions, gypsum crusts, and the identification of brown streaking apparent on the facade that was believed to be an earlier treatment coating.

Previous testing of the Pennsylvania Marble at the Second Bank was done for portions of a graduate thesis in 1996 by Jocelyn Kimmel, at the First Bank as part of a graduate thesis in 1998 by Guy Munsch, and at the Merchant's Exchange as part of a multi-year Conservation Strategy (Brookover, McGee, Mossotti, Dolske and Sherwood, 1992). Further analysis and testing of the stone will proceed once the exterior conditions survey has been completed. Testing as required to evaluate specific treatment and repair strategies will also need to be incorporated into the future phases of the project.

Scanning electron micrograph (SEM) taken from the north facade of the Second Bank of the United States displaying the blistered surface of an external coating on the marble.
Scanning electron micrograph (SEM) taken from the north facade of the Second Bank of the United States displaying the blistered surface of an external coating on the marble.

The scanning electron micrograph (SEM), on the right, shows a coating which has blistered on the surface of the marble exposing the stone surface through the opening near the center of the image. To confirm the visual observations, an EDS analysis was performed. A central target inside the opening of the coating was selected and an elemental spectra was taken and recorded. A second target over the coated surface was then used for a second reading.

The spectra below on the left shows the marble surface without the coating. It exhibits a high calcite (Ca) peak with minimal readings for silicon (Si) and iron (Fe). The spectra below on the right, taken from the coated area, still has a high peak for the dominant mineral of the marble, calcite, but there is a substantial increase in the silicon and the iron peaks. The silicon confirms the presence of the silicone based waterproofing polymer coating. The iron that would normally be present in the stone in small amounts and would naturally weather off of the surface is held just below the surface of the film contributing to the orange brown staining on the surface of the marble.

Spectra from area of exposed marble surface and Spectra from area where brown coating is present on marble.

Spectra from area of exposed marble surface.

Spectra from area where brown coating is present on marble.


Several samples were taken from the north facade of the Second Bank in 1999. Following, are short summaries of a range of samples tested using X-ray diffraction analysis to confirm physical compositions of some of the more prominent inclusions, a white powdering on the surface, and "gypsum" crusts. To view a reference drawing of the locations from where the samples noted below were taken, click here. All original samples and laboratory data have been deposited at the INHP archives.

Analyses were conducted on stone samples using an X-Ray Diffraction Rigaku Diffractometer at the Laboratory for Research on the Structure of Matter (LRSM) at the University of Pennsylvania. The instrument was set at kilovolts and milliamps. The scans were run between 5 and 65 degrees 2T, at 2 degrees per minute. All of the samples were reduced into powder with a mortar and pestle. A glass slide was prepared by covering it with a thin layer of vaseline and spreading the powder over it.

  • Marble Dust
    From an unknown area of the North facade (ground collection)
    XRD, Files     Z12228.raw and Z12228.pks
    Best match for marble dust is JCPDS spectrum 72 1651, calcium carbonate (calcite). The Pennsylvania Blue Marble is mainly composed of calcite (CaCO3).
    Secondary minerals from the marble did not display any prominent peaks.

  • Mineral Inclusion 1 (MI.1)
    XRD, Files Z12229.raw and Z12229.pks
    Best match for mineral inclusion 1 is JCPDS spectrum 83 0577, calcium carbonate. A secondary search was carried out on the spectrum of mineral inclusion 1 minus 82 0577. Two good matches of the resulting spectrum were JCPDS spectrum 06 0263, potassium aluminum silicate hydroxide (muscovite 2M#1) and JCPDS spectrum 40 0020, potassium magnesium aluminum silicate hydroxide. It is expected that calcite is the dominant mineral since almost all samples were sampled by scraping the stones, and are mixed with marble dust. The mineral inclusion is probably a type of muscovite.

  • Mineral Inclusion 2 (MI.2)
    XRD, Files Z1 2230.raw and Z1 2230.pks
    Best match for mineral inclusion 2 is JCPDS spectrum 06 0263, potassium aluminum silicate hydroxide (muscovite 2M#1). Second best match is JCPDS spectrum 76 0929, potassium aluminum oxide silicate hydroxide (muscovite 2M1). Calcite does not appear as a dominant mineral in this sample. It is probably a relatively pure sample of the inclusion, minimally contaminated by the marble dust. Mineral inclusion 2 is similar to mineral inclusion 1. It belongs to the muscovite mineral family.

  • Mineral Inclusion 3 (MI.3)
    XRD, Files Z12231.raw and Z12231.pks
    Best match for mineral inclusion 3 is JCPDS spectrum 77 2255, potassium aluminum silicate hydroxide (muscovite). Second best match is JCPDS spectrum 76-0929, potassium aluminum oxide silicate hydroxide (muscovite 2M1). JCPDS spectrum 40 0020, potassium magnesium aluminum silicate hydroxide, second best match for mineral inclusion 1 is the sixth best match of mineral inclusion 3. JCPDS spectrum 6 0263, potassium aluminum silicate hydroxide (muscovite 2M#1), best match for mineral inclusion 2 is the seventh best match of mineral inclusion 3. Mineral inclusion 3 is similar to mineral inclusions 1 & 2. It belongs to the muscovite mineral family.

  • Mineral Inclusion 4 (MI.4)
    XRD, Files Z12232.raw and Z12232.pks
    Best match for mineral inclusion 4 is JCPDS spectrum 5 0586, calcium carbonate (calcite). A secondary search was carried out on the spectrum of mineral inclusion 4 minus 5 0586. The best match of the resulting spectrum was JCPDS spectrum 82 1572, silicon oxide. The second best match is JCPDS spectrum 76 0668, potassium aluminum silicate hydroxide (muscovite 2M1). A tertiary search was carried out on the spectrum of mineral inclusion 4 minus calcite (5-0586) minus muscovite (76 0668). The best match of the resulting spectrum was JCPDS spectrum 42 1340, iron sulfide (pyrite). Mineral inclusion 4 has a different color and appearance than mineral inclusions 1, 2 and 3. The three first were gray and very layered, almost fibrous. Number 4 was red brownish and of a smaller quantity. The best match of mineral inclusion 4 minus calcite is silicon oxide. (Note: As later testing confirmed evidence of a silicone based coating, the results of this test would seem to reflect the presence of the coating material on the marble sample.)

  • White Deposit 1 (W1)
    XRD, Files Z12233.raw and Z12233.pks
    Best match for the white deposit is JCPDS spectrum 70 0984, calcium sulfate hydrate (gypsum). This white deposit is present in areas which may not receive rain water washing through direct exposure or run off.

  • White Deposit 3 (W3)
    XRD, Files Z12244.raw and Z12244.pks
    Best match for the white deposit is JCPIDS spectrum 72 0596, calcium sulfate hydrate (gypsum).

  • Gypsum Crust 1 (G1)
    XRD, Files Z12246.raw and Z12246.pks
    Best match for gypsum crust 1 is JCPIDS spectrum 72 1650, calcium carbonate (calcite). A secondary search was carried out on the spectrum minus 72 1650. The best match of the resulting spectrum is JCPDS 6 0046, calcium sulfate hydrate (gypsum).

  • Gypsum Crust 2 (G2)
    XRD, Files Z12247.raw and Z12247.pks
    The best match for this sample is JCPDS spectrum 70 0095, calcium carbonate (calcite). A secondary search was carried out on the spectrum minus 70 0095. None of the matches proposed by the database for the secondary search was appropriate for this type of sample, gypsum did not appear in the spectrum. The sample appears to be a soiled sample of friable marble, but is not in a deterioration state that has produced a true gypsum crust. The analysis underlines the difficulties in distinguishing a real gypsum crust deterioration pattern from a surface soiling of the marble.

  • Gypsum Crust 3 (G3)
    XRD, Files Z12248.raw and Z12248.pks
    The best match for this sample is JCPIDS spectrum 72 1652, calcium carbonate (calcite). A secondary search was carried out on the spectrum minus 72 1652. The best match of the resulting spectrum is JCPDS spectrum 6 0263, potassium aluminum silicate hydroxide (muscovite 2M1). A tertiary search was carried out on the sample, the third best match is 78 1253, silicone oxide (quartz alpha). The sixth best match is 36 0432, calcium sulfate hydrate (gypsum). The sample contains the dominant mineral from the marble, calcite, and from an apparent inclusion, muscovite, there are traces of the silicone treatment coating and of a mild gypsum crust.
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