Tin and lead, both easily processed materials, have always been the metals of choice for organ builders. Organ pipes made from tin alloy are favored not only for their visual beauty but also for their mechanical and acoustical properties as well as for their longevity. It has recently been discovered that otherwise well-preserved pipes from the 17th century are suddenly showing signs of serious corrosion.
Until about 80 years ago, metal was more expensive than labor. It was therefore common practice to recycle Sn-Pb alloys in the construction of new pipes. Old pipes were sent to the melting pot along with scraps from any available source. Even virgin smelter metal showed traces of foreign elements because the techniques needed to produce pure metals had not yet been developed.
Occasionally, the presence of foreign trace metals had the advantageous effect of creating hard, somewhat creep-resistant alloys. Many pipes made with such alloys have survived. Whether these were the result of coincidence or of specific knowledge remains speculation. However Dom Bédos de Celles’ 1770 treatise, L’Art du Facteur d’Orgues, provides detailed instructions for the production of good pipe metal. Until well into the middle of the 20th century, organ pipes were often produced from scrap metal alloys and showed corrosion damage after only a few decades. Presumably similar patterns existed in earlier centuries. When corrosion appeared, instruments were either rebuilt or simply replaced. Only the very best survived.
The famous organ of St. Jakobi, Lübeck, dates back to the year 1467 and provides invaluable insight into the music of the Renaissance and the early Baroque. It has been known as the “Stellwagen Organ” since the 17th-century rebuild by the organ builder of that name. In 1992, it became apparent that the large pipes, made of nearly pure lead, have been gradually losing their voice. Corrosion has taken the form of small holes in the pipe metal. Other valuable organs like L’Aquila north of Rome and Oegstgest north of The Hague are also suffering from corrosion, while on the other hand many organs from the same period show no evidence of corrosion.
Many physical illnesses are preceded by an incubation period. Perhaps the same may be true of pipe metal corrosion. Although the affected organs remain in their original locations, the environment within their buildings may have changed. Often, interior restoration involves the application of chemicals such as acid, lye, ammonia, thinners, etc. Renovated walls, ceilings and floors may incorporate new materials that introduce, for example, acetic acid from new oak. Stain and corrosive fluids, in conjunction with high humidity, can promote lead corrosion even in relatively new pipe metal. Newly installed heating systems can create fluctuations in temperature and humidity and can generate dew points at the building walls and even within the organ. With almost no ventilation provided in ancient church buildings, relatively little exchange of air is possible. Conversely, today’s modern heating and ventilation systems can exchange the air in a whole room within a short time, including that within the organ.
With increasing tourism, more dust, humidity and carbon dioxide is carried into venerable old church buildings. Air currents carry charged, sooty dust particles to the pipes, where they precipitate with the vapor of the visitors and moisture at the dew point to produce a light chemical cocktail. This, together with increased levels of carbon dioxide, can attack pipe metal. Organ builders are all too familiar with the carcasses of dead flies, bats and birds in organs. Their excrement on pipes is a common cause of corrosion. Even the droppings of flies and spiders can be so aggressive that a nucleus for corrosion can form under supportive environmental conditions.
Techniques have been developed to stop corrosion in organ pipes made of tin. The pipes are cleaned and placed into a neutralizing liquid, then into a dilute electrolyte solution. Within the solution, a sheet of austenitic steel is connected to the anode of a power supply, while the organ pipe is connected to the cathode. Under the flow of electric current, the oxidized coating of the tin surface is removed, revealing the naked metal beneath. This process has been applied to the 99.5% tin façade pipes of the 1743 organ in the Cathedral of Dijon.
Lead organ pipes exhibit a different damage profile than those of tin. Environmental conditions such as those described above are assumed to be the cause of damage. A cure will likely be more difficult to find, since the corrosion process of lead involving lead white or lead acetate is not presently reversible.
Lead (II) acetate, commonly called salt of saturn, lead white, lead carbonate or sugar of lead, is a solid, colorless, white solid that was used by the Romans to sweeten wine. It was also known as the Viagra of antiquity. Unfortunately, the price for excessive consumption was the beginning of infertility. Perhaps this is why the Romans were the first to have adopted children.
In 300 BC, Theophrast described the production of lead white. In oxidation rooms, up to ten tons of lead plates were placed in stone pots packed with oak bark and horse dung. The heat of the dung, in conjunction with the acetic acid of the bark and carbon dioxide in the air, caused the lead to disintegrate into a white powder (lead white) in only four weeks. In ancient times, lead white was used for makeup and, until the 20th century, as pigment in paint. When heated, lead white first turns red (“Massicot”), then yellow. When sulphur is introduced, black lead sulphide results; we know it as graphite.
As an apprentice in organ building, and later in the Masters’ course, the writer became familiar with tin plague or “tin pest.” Teachers explained the chemical reactions that convert beta to alpha tin, and the terrible, irreversible damage that results. In the almost 46 years of his career as an organ builder, the author has seen many types of damage to organ pipes, but true tin plague could almost never be verified. The first pipe with confirmed tin plague was shown to the author in Estonia in 2000. Sometimes damage by saltpeter (potassium nitrate, often found in fertilizers) or other corrosive agents has been attributed to tin plague in order to stress the severity of a problem. Indeed, damage by such corrosive agents can be just as devastating, even though not actual tin plague.
Corrosive damage to organ pipes is increasing. This is undisputed, and some of the famous historic organs of Europe are suffering from it. Within the span of only a few years, ancient organ pipes have suddenly exhibited frightening signs of disintegration. Organ builders and curators are struggling to understand the phenomenon and to find a means of rescuing these instruments, preserving their unique sound portraits and preventing such damage in the future.
Since there had been little research into this issue, project COLLAPSE has been established and has been funded by the EU in Brussels with an initial grant of 900,000 euros. COLLAPSE (Corrosion of Lead and Lead-tin Alloys of Organ PipeS in Europe) is headquartered at the GOArt Centre in Göteborg, Sweden (www.goart.gu.se/collapse/). The University of Göteborg Department of Inorganic Environmental Chemistry, as well as the University of Bologna Metallurgic Institute, will assist in the research. Although COLLAPSE deals mainly with lead corrosion, there is also awareness of tin corrosion and tin plague, and these may become the subjects of future projects.
It is planned that the lead pipes of the St. Jakobi Stellwagen organ be coated with protective resin in order to close the small holes that have developed in the pipe metal. The resin coating would also protect the metal from further damage. Artificially produced resins would be used on a temporary basis until a cure or a more permanent remedy can be found. Modern principles of monument conservation require that any work done on original materials be reversible. Therefore any such resin that might be applied now must be removable without the damaging effects of solvents. This leaves open the possibility that new techniques and better understanding might allow restoration to near original condition at some future time.
It is hoped that after the EU funds have been expended, new knowledge and techniques to resolve these problems will have been developed and that our valuable cultural heritage will be preserved for future generations.
