Project Focus:
The Historical Society of Pennsylvania:
Philadelphia, PA
Masonry Conservation, Specifications
Consultation, Construction Supervision

The Historical Society of Pennsylvania is one of the nation’s most influential and prestigious historical research institutions. Its collections include more than 500,000 books, 300,000 graphic works, an extensive manuscript collection, and serve as the Mid-Atlantic region’s largest repository for genealogical information.  Architecturally, Horace Trumbauer's 1906 work is a Federal Revival composition executed in brick with marble ornamentation.  

Our work at HSP has also yielded important information about the conservation of Pennsylvania Blue Marble, a locally significant building material which is highly susceptible to deterioration in an urban environment.

Quarried in nearby Chester and Montgomery Counties, this stone experienced its highest levels of popularity in the 18th and 19th centuries, which suggests that the 1906 Historical Society of Pennsylvania may be one of its latest large-scale uses.  Often selected for its rich color and texture, it was an extremely workable stone which could be carved into elaborate detail, and one which provided an inexpensive alternative to imported European marbles and marbles from elsewhere in the United States. 

Our 1996 conditions survey for Venturi, Scott Brown and Associates concluded that the stone's relatively weak internal structure played an important role in its deterioration,and if left unchecked, that deterioration would most likely accelerate.  Further study found that the weak recrystalization of the marble renders surface grains more reactive to gypsum alteration than they might otherwise be, and that weak intergranular bonds enhance the likelihood of deformation due to disaggregation and delamination. 

We completed a documentary search of previously-completed projects, constructed testing matrices and completed a series of mock-ups before writing project specifications.  Based on results obtained on-site and examination of samples in the laboratory, we opted for a conservation program which included gentle cleaning with the JOS Water-Microabrasive system to remove surface contamination and selective consolidation to stabilize certain surfaces at risk of immediate loss.  Because of the delicate nature of the stone and the desire to retain as much original material as possible, Noble Preservation supervised the work in its entirety to ensure quality cleaning without damage to the stone.

Given the sensitivity of the marble, we supervised the JOS conservation-cleaning of the portico to continually evaluate the procedure's success.

Performed properly, we found that cleaning with JOS preserved important details and did not damage the stone.