New Hampshire State House
The monumental dome on the New Hampshire State House is gilded in gold leaf. After regilding in the early 1990s, the gold leaf started discoloring. The state wanted to understand the cause of discoloration and identify any inherent problems prior to restoring the dome’s gilding. SGH investigated the discoloration and subsequently worked on the regilding project.
Using a crane-suspended basket, SGH performed a hands-on survey of the dome, performed in situ adhesion testing, and obtained samples for testing. We observed discoloration of the copper substrate, delaminated/missing gilding, and abrasion and wearing of the gold leaf. In our laboratory, we used a scanning electron microscope to examine the gilding and performed chemical analyses of the samples.
SGH determined the discoloration was primarily due to installation procedures and that damage from access equipment and birds lead to abrasion and wearing. We provided recommendations to help the project team mitigate these problems in future applications.
The architect subsequently retained SGH to work on the dome gilding restoration. We researched gilding processes, developed a gilding specification, and provided construction phase services, including reviewing samples and visiting the site to observe ongoing work. Based on our recommendations for mitigating abrasion, the project team developed an exterior scaffolding system that would not contact the dome structure and was instead supported off an internal platform.