The Statue of Liberty (Liberty Enlightening the World), a colossal sculpture on Liberty Island in New York Harbor, underwent an extensive conservation-restoration between 1984 and 1986, in advance of its centennial. The statue, designed by French sculptor Frédéric Auguste Bartholdi, is part of the Statue of Liberty National Monument. International attention to the Statue of Liberty's poor state was called upon the restoration of similarly-built Aimé Millet's Vercingétorix statue in eastern France. Much of the Statue of Liberty restoration effort was based on unprecedented restorative methods, as metallurgical repair work on such a large scale had never been attempted. Many scientists, engineers, government organizations, and professional consultants evaluated and dealt with the various problems and tasks facing the restoration effort.

The restored statue was reopened during Liberty Weekend, its 100-year anniversary celebration held July 3–6, 1986.

Pre-restoration documentation efforts

The preparations for the centennial celebration of the Statue of Liberty began in 1979. The centennial conservation-restoration project was formed by the National Park Service (NPS), the custodians of the statue since 1933, to investigate possible development alternatives. A report titled "Analysis of Alternatives", published in December 1980, proposed measures to remedy the certain conditions confronting visitors to the Statue of Liberty, such as the long lines and waiting time to enter the crown of the statue. The proposed measures included the instatement of systems for numbered ticketing and early warnings that would allow visitors to estimate any possible waiting times and to be conveniently advised if and when to visit or enter the statue. The report also discussed ways to streamline ferry access both to and from Liberty Island and Ellis Island. The early report did not address the ever-deteriorating physical condition of the statue, which was already readily apparent.

The French American Committee for the Restoration of the Statue of Liberty was formed in May 1981.Blumberg, B., "Celebrating the Immigrant: An administrative History of the Statue of Liberty National Monument," p.139-140. The Department of the Interior (of which the National Park Service is a bureau) later that month, on May 26, agreed to a working relationship with the Committee. In June 1981, the Committee was incorporated as a non-profit foundation licensed by the State of New York to raise funds for the restoration effort. The Committee hired four French consultants said to have considerable expertise in their respective fields: an architect-engineer, a metals expert, a structural engineer and a mechanical engineer who were asked to compose a technical report on the physical condition of the statue. The French consultants visited Liberty Island in May, June, October and December 1981, before presenting a preliminary white paper to the National Park Service on the seventeenth of December in Washington, D.C., titled "French Technical Report on Restoring the Statue of Liberty".Also see Cliver, E.B. and Baboian, R., "Corrosion on the Statue of Liberty: an overview". In: The Statue of Liberty Restoration: Proceedings of the Statue of Liberty - Today for Tomorrow Conference, October 20–22, 1986, New York City, New York. [Ed. Baboian, R.; Bellante, E.L; Cliver, E.B.], Houston, Tex.: National Association of Corrosion Engineers, 1990, 149 pp.

The report, written with the assistance of a regional historical architect from the NPS, was an attempt to identify and address the apparent problems associated with the statue. In the report, the consultants took note of what they saw to be the most serious problem affecting the statue: that two predominant sections, the torch-bearing arm and the rest platform at the head level, had corroded significantly. The report also alluded to the corroded girders toward the top of the pedestal and the bottom of the central pylon. The report also discussed the serious structural problems associated with the long-ago deteriorated insulating layer between the copper sheet of the statue and the iron bands of the structural armature, as it had caused the iron bands to corrode. Alterations over the intervening years (1887–1916) to the torch had created such irreversible damage to the integral stability of that segment, that it was advised in the report that the torch be replaced. In order to more thoroughly assess possible damage that may be hidden beneath the layers of paint on the central pylon, the French consultants also suggested that the layers of paint covering it be removed. Two alternative proposals for modernizing the stairway within the statue were also proposed. From these preliminary observations, a number of preservation and replacement priorities were made. The white paper was further assessed and scrutinized by the NPS and other officials at the Department of the Interior in the nation's capital on March 5, 1982. The director of the NPS was impressed by the report, but also concerned about the future prospects of the Committee's fund raising efforts.

Shortly thereafter, the Secretary of the Department of the Interior announced in May 1982 the creation of a 21-member Statue of Liberty-Ellis Island Centennial Commission (better known as the Statue of Liberty-Ellis Island Foundation) which would act as an "umbrella group" overseeing the French American Committee and the Ellis Island Restoration Commission. The Statue of Liberty-Ellis Island Foundation would try to privately raise funds for the restoration efforts. A report prepared by the NPS in September 1982, titled "General Management Plan", sought to discuss the fundraising aims and objectives of the newly created foundation, but reiterated most of the proposed measures (concerning the statue) of the earlier 1980 report "Analysis of Alternatives" (such as numbered ticketing systems, etc.).

Earlier in 1982, the French American Committee began looking for U.S. consultants to complement the technical work already begun by the four French consultants. They would need to prepare a detailed diagnostic report to investigate the conditions of the Statue in further detail, as many of the French consultants were unfamiliar with the construction procedures and standards, and the design and business practices employed in the United States. Several architects, structural engineers, and representatives from the NPS were brought aboard on the project. Construction work would be assigned to U.S. contractors, and by July 1983, a joint diagnostic report was completed by the newly joint group of consultants and presented to NPS officials. By December 1983, the U.S. group assumed many of the responsibilities concerning the design aspect of the project, and by August 1984, the U.S. team terminated its contract with the French American Committee, owing to the Committee's considerable fundraising problems and other related matters. The associate architect for the restoration was Thierry Despont, who would later rise to prominence as the architect of homes for Bill Gates and Les Wexner.

Just prior to the restoration efforts, there were an insufficient number of photographs documenting the initial reassembly of the statue (when it had been given), and too few photographs documenting the condition of the statue since its construction that were relevant to the maintenance of the statue. The NPS vowed to support the historical documentation effort, and a photographer was hired to photograph the entirety of the restoration—before, during, and after. Owing to this decision, an archive of two hundred large format photographs—both black and white, and multicolor—were developed for NPS and the Historic American Engineering Record (HAER). According to The New York Times, the American Society of Civil Engineers (ASCE) would also be donating a set of three-dimensional computer drawings of the statue, rendered in the computer-aided design (CAD) program. The drawings were to aid in the future maintenance of the statue. These drawings were later given to the NPS, and were important in analyzing the wind bearing capacity of the structure within the statue.

Implementation of diagnostic assessments

Early beginnings

From November 7, 1982, public announcements were made by project officials that the Statue of Liberty would be completely closed to the public for as long as one year beginning in 1984. The statue had been closed only once before for such an extended period of time, and that was at one point in the late 1930s. Later announcements stated that the erection of the scaffolding surrounding the outside of the statue would begin in the fall of 1983, and it was still believed in July 1983 that the restoration would begin sometime in the fall. NPS representatives retracted and revised the earlier announcement concerning the closure of the Island to the public; Liberty Island would in fact remain open and closings would be intermittent and only for several days at a time at most. The restoration would not begin until January 23, 1984. An article from The New York Times published the day after, indicated that the 30-month project had officially begun the day before, and that visitors would have approximately two weeks remaining before the statue would be completely enshrouded by the tons of extruded aluminum scaffolding that had just been deposited on Liberty Island.

The scaffolding contract was awarded to a company called Universal Builders Supply (UBS) Inc. on December 14, 1983. The contract stipulated that the freestanding exterior scaffold was to be completely assembled by April 27, 1984. The scaffolding was designed specifically for the statue, and required ingenuity from its designers, as it could only be attached to the granite pedestal and not the statue and had to accommodate the intricate contours of the statue as well. Furthermore, the exterior scaffolding had to maintain a distance of at least 18 inches from any exposed section of the copper sheathing. The 6,000 or so separate components of the scaffold, made of a high load capacity aluminum (alloy 6061 T6), were unloaded onto Liberty Island on January 23, 1984. Aluminum was used to prevent possible rust stains from affecting the exterior patina of the statue. Screw jacks were used to brace the aluminum against the granite pedestal of the statue. More easily an interior scaffolding was developed made of interlocking pipes held together with friction clamps and anchored to the central pylon of the statue for structural support. The twenty UBS workers often resorted to assembling the interior scaffolding when the severe winds and dreadful winter weather conditions prevented them from continuing their work outside.

Interior coating removal

Once the interior scaffolding was installed, a thorough evaluative survey of the interior coatings was executed. The acknowledged presumption of most involved in the restoration was that all coatings would be removed from the interior metals, that repairs would be made, that metals would be recoated, and the interior would be adequately weatherproofed. The preexisting interior coatings on both the secondary wrought iron framework and the wrought iron central pylon would be removed along with the multiple layers of coal tar and paint that had been applied to the internal copper sheathing. An article in The New York Times of February 8, 1984, mentioned that the interior copper which was at that time painted "government green" would be cleaned to resemble the salmon color of a new penny. That outermost "government green" layer was a vinyl paint applied in 1975.