to clean the marble surface without damaging the material. Arch reproduction and patinization In the process of removing of the 1947 and 1950 third-floor additions, Page & Turnbull discovered the extent of the damage to the brick and terra cotta arches of the nave. Twenty-two arches span the length of the nave on each side, and of the 44 total, 11 had been destroyed. Over 25 percent of the original material had been removed in the first remodel, including terra cotta scroll-work, the arches themselves, and sections of the surrounding brickwork. In order to restore the highly significant nave, Page & Turnbull had to design and create replacements for these 11 arches that would be accurate enough not to detract from the sight line of the second story that these arches flank. The prohibitive cost and effort of replacing these materials in kind led to the choice of a cast-stone with fiberglass support that mimics the buff brick in both color and finish. Through the use of a cast material, Page & Turnbull was able to create a fiberglass mold to be used for casting each arch as a unit that could then be inserted into sections where original fabric had been lost. The addition of fiberglass as a support material—that allows for both flexibility and compressive strength—was seen as an added benefit in meeting concerns over the building's continued seismic safety. Creating visual continuity between the new and the old was critical in this instance due to the significance of the long stretch of the nave; here an obvious alteration in material or color would detract from the pattern of springing arches that continues through the length of the structure. Page & Turnbull invited faux-finishing specialist Jacquelyn Giuffre to disguise the new sections and recreate the continuity of pattern and color. Guiffre's job was made more difficult by the fact that the structure had not been completely sealed against the elements during the restoration and the salts of the bay air triggered a staining process that created green marks in the yellow and buff brick. In order to match the texture and patina of the old brick, Guiffre used six different pigments applied by hand, and then applied green shading to mimic the new staining process. Once the pieces were installed, a final stage of blending was completed on site to ensure the greatest possible accuracy. Clocks The original