PIPEMAKING

David Smit

davids@astrolabegroup.com

Metal Pipes — Part I: Metallurgy

Contents

Introduction
Pipemaking Materials
Metal Properties, Structure, and Ageing
Metal Analysis and Composition
Metal “Diseases”
Metal Dangers

Introduction

The purpose of this series of papers is to review various technical topics related to the making of organ pipes. The first paper (this one) discusses the various metals and alloys commonly used in pipemaking, their physical and chemical properties, and some special characteristics that may give rise to problems.

A few general remarks beforehand might not be out of place. I have tried to give both Imperial and metric measurements as far as possible. As a rule I go to only one decimal point as anything finer than that is usually not practically significant. The obvious exceptions are metal thicknesses and percentages. I have also tried to stick to one unit as far as possible.

I take as a point of departure for discussion the casting of high lead alloys. The reason for this is that the tin casting and spot casting are mere simplifications of this technique. However there are some differences; these are noted in the body of the discussion.

Some of the sources mentioned in the bibliography are either very general or dated in their approach and are not quoted directly in this paper, but are mentioned for the sake of completeness. I have shied away from quoting too much from any one particular source in the case of the older works, as that necessarily promotes that writer's opinion. Particularly in the case of Audsley, who can be very verbose, I have tried to extract only the facts.

I must here express gratitude to the numerous correspondents on the PIPORG-L electronic mailing list who have contributed to the subject over the years in their postings to the list. PIPORG-L is the single largest source for this document. In this same vein, readers are urged to suggest to the author corrections and improvements to the end of making these papers ultimately as useful as possible.

Pipemaking Materials

To set the stage for discussion, I reproduce below an article by Charles Fisk (published 1978 - AGO/RCO Magazine). This article, along with “The Organ's Breath of Life” (1969) were the pioneering works that set pipemaking trends for the latter part of the 20th century.

Some Thoughts on Pipe Metal

Charles Fisk

As I write this, the price of tin hovers around six dollars per pound. Five years ago it was less than three dollars. For organ builders, most of whom tend to feel that their instruments are already too expensive, the rise of tin price has been a throughgoing headache.

Each builder in his own way has sought relief from the tin price problem. Some have shifted upward the breaking point between their zinc basses and their tin alloy trebles. Others have cut their spotted metal from a flashy 52% to the old prewar 42%. Flutes that once were made of spotted metal are now made in common or Hoyt's metal. Polished tin façade pipes, ever a luxury, are now regarded as a shocking extravagance. And some builders are beginning to use 97% lead for a large part of their flue work; these builders are, in effect, turning their backs on tin as a material for organ pipes.

If you look inside an EM Skinner organ of the 1920s, you are made aware that in America tin was not always used on the extensive scale we have come to regard as normal. G. Donald Harrison, Ernest Skinner's successor, was the man who started us all on our tin habit, a habit later much intensified by the postwar Dutch, German, Swiss and Danish export builders who often used tin alloys for all bass pipes, thus eliminating zinc entirely from the organ. Nowadays most organists will tell you that tin is good, lead is not and zinc is something one tries not to talk about. (Most organ builders agree zinc is primarily a metal of convenience. Large bass pipes made of soft metals like lead and tin are very difficult to handle in the workshop and in transit without denting; zinc has more strength for its weight and produces a very durable pipe.)

But if there is little argument over zinc, the lead versus tin argument cannot be disposed of so easily. Centuries old, it has always had to endure the influence of the cost factor, one aspect of which is the popular assumption that the more expensive metal produces the better sound.

If American organ building, through economic necessity, is headed for more lead, does this mean a loss of quality for America's future instruments? For an answer to this question we should consult history.

Tin has always been an expensive metal, and while it boasts a long history of use in organ building, the fact is that “pure" lead - without any additions whatever - was the normal material for making organ pipes almost up to the time of Schnitger. (By “pure” lead I mean the purest lead available at the time, i.e., a metal which analyses at around 97% lead and 3% trace metals which the refining process of the time could not remove.) Schnitger rebuilt a great many Gothic and Renaissance organs, and what a scavenger he was! He never threw aside any stop that in his eyes had virtue. We thus find in his organs stop after stop from earlier builders made of pure lead. His elegant organ at the Aa Kerk in Groningen retains many old stops, including de Mare's 16, 8 and 4 foot foundations for the Great chorus. These are of “pure” lead and lend a surpassing dignity to Schnitger's instrument. Interestingly enough, Schnitger often saved the lead foundation stops but habitually threw out the lead mixtures he found in the Gothic and Renaissance organs, preferring the schneidern quality of his own mixtures, which were usually made with about 20% of tin.

What are the characteristic sounds of the old lead stops? First, a darkness, a hollowness, a sound as of deepest antiquity. Second, an astonishing agility, an ability to move as the music moves, to flit about like a freshly hatched insect. These two characteristics seem contradictory, and indeed, as I see it, the attractiveness of lead pipes seem to lie in the paradox that qualities of youth and great age can cohabit the same mysterious envelope.

Another paradox relates to the strength of the sound. A lead pipe, when voiced in the old way, yields a tone with a softness about it, an unformed, amateurish kind of tone. Yet a chorus of lead pipes produces resultants of great carrying power. Lead is what gave the small Gothic organ the power to fill a vast cathedral. Recall the little organ at Oosthuizen and its “brave sound,” as E. Power Biggs so aptly titles it. That bravura, that all-out quality, is the sound of lead.

What, alternatively, is the sound of tin? I think of it as the sound of refinement, the argentine sound of the French Plein Jeu, or at its very best, the blaze of weightless color and light that Gottfried Silbermann knew so well how to achieve in his paper-thin, hammered tin choruses. Tin pipes love to produce overtones, and there is something about the metal that lends itself to the production of pleasing overtones, particularly when the voicing is done in the old way, with high cutups. This is how the “silver” of Silbermann is achieved. In our own time, unfortunately, there has been a widespread tendency to make tin pipes with walls that are thick (a waste of material) and with cutups that are low ( a French technique) and with toeholes that are wide open (a German idea). No wonder that upperwork made in this polyglot way is piercing beyond the bounds of music; no wonder that foundations so constructed are foundationless and characterless. Low cutups put the tin in a bad mood, so to speak, whence it cannot rise to its natural elegance. I believe the misapplication and abuse of tin will come to be seen historically as the great organ building mistake of the '50s, '60s, and '70s.

Those Americans wishing to seek out the virtues of lead might appreciate a few reflections on the problems lead presents for the manufacture of organ pipes:

a. Lead is difficult to cast into sheets because of the high temperature required and because there is no pasty stage as there is in the lead/tin alloys. Casting must be done on a fiberglass or Nomex cloth; cotton or linen will disintegrate.

b. Pig lead available on the market is generally so pure as to be dead soft and must therefore be doctored. By adding some of the impurities that come naturally in the old “pure” lead of the 17th century, the metal can be made sturdy enough to stand for many years. Antimony (0.75%), copper (0.06%), bismuth (0.05%) and tin (1.0%) when added all together will produce the desired stiffening. Curiously, lead with these trace elements scarcely creeps at all; ordinary common metal (20% tin, 80% lead) creeps far more. This explains why the lead front pipes from the Gothic and Renaissance stand without any sign of collapsing, while American common metal front pipes of the early 19th century always sagged. Adding tin to the lead actually increases the creep. (For this information our whole trade is indebted to Herman Greunke, organ curator at the Oberlin Conservatory of Music, who is a learned source on the subject of lead technology as applied to organs.)

c. The tone seems best when the metal is hammered. When cast, 97% lead is particularly porous. It seems not to be hardened by hammering, but it is made more dense, and this is apparently helpful. Cavaillé-Coll says, “Hammering renders the metal more dense and more sonorous.” Cor Edskes maintains that hammering causes the pipe to speak more quickly.

d. Lead pipes require less nicking than do tin-alloy pipes, particularly if there is a small counterface [counter-phase] (Gegenphase) on the leading edge of the languid.

e. Scales that are right for tin or spotted metal will be too large for lead. A lead stop should be two to three scales smaller than its tin-alloy counterpart. People have often wondered at the slender scales of the front pipes in Dutch and German cases of the Renaissance. These scales were correct for lead, and the organs they served were by no means the bass-hungry devices we might imagine them to be.

f. It is useless to try for an edgy or stringy sound from "pure" lead. Not that it is impossible; indeed a low cutup mouth sharply skived will produce a surprising array of overtones. But it is as if the pipe were saying to the voicer, “All right, I'll do it your way, but you aren't going to like it.” There is something heavy and unpleasant about the overtones thus forced from lead. The solution is to cut the pipe up until the mouth is no longer imposing its will on the resonator and the tone is relatively free of “mouth engendered” overtones. A lead mixture pipe when cut up high enough sounds a little like a traverse flute, especially when blown by mouth.

Returning to Cambridge after one of his many European trips, the late E. Power Biggs was heard to say, “There must be at least a dozen ways of building an absolutely perfect organ.” This brings to mind Landowska's famous pronouncement, “In art there is no progress - only change.” Clearly an organ's artistic merit does not depend on whether its builder uses lead or tin for his pipes but on how he uses what he uses. It is a simple question, really: If American organ builders wish to rely more on lead than they have in the past, let them consider the masterful examples set by the de Mares and Schnitgers of our world, and then let them apply their own unbiased ears and their own immutable good taste.

[Reproduced with permission.]

Another interesting perspective is that given by John Brombaugh in his comments in The Historical Organ in America:

High quality pipework in an organ is its most valuable asset. With an unusually positive and congenial working relationship, a small group of world-class American organ-builders make their own pipes while sharing their ideas, research, and errors with each other. It is a phenomenon unheard of among European builders, even the best. We go to Europe, look at, listen to, and study the ancient instruments, and then work out ideas so we might get results similar to the old masters. The Europeans help, too, as when Maarten Albert Vente gave me several years ago several large Praestant pipes in 1971 made by Hendrik Niehoff's shop for the 1539 organ in Schoonhoven, Holland. Our shop analyzed them, let Charles Fisk and Gene Bedient (plus Paul Fritts, Manuel Rosales, and others later) study them, and finally started making our own pipes in 1975 for Opus 19 (at Central Lutheran in Eugene [Oregon]) utilizing the results of our studies. The alloy is primarily lead (over 98%) with only a bit more than 1% tin and small amounts of antimony, copper and bismuth. These minor portions, however, are absolutely necessary to ensure structural stability to the alloy. A look at historic organs from the 1500's indicates it to be quite practical and stable as found, for example, in the ancient pipes from Niehoff of 1550 and Dirk Hoyer of 1580 in the Johanniskirche organ in Lüneburg. The alloy structure, however, is not the only important factor; the metal must be properly hammered to make good pipes. Unlike iron and brass, tin-lead alloys do not get harder when hammered; hammering stabilizes the metal's crystalline structure to improve the structural stability and the sound of the pipe. It was a must for organbuilders from the earliest times through Dom Bédos' period. Pipes made from a hammered high lead alloy sing that special vocale sound so cherished in the ancient organs.

But hammered high lead is not the answer to all musical requirements; higher tin alloys also have musical benefits for the upper registers in the principal plena, some reed resonators and, of course, string stops. Here, as in so many cases, it is a question of style, since, except possibly in the facades, one seldom finds anything but high lead pipes in the northwest European (especially Dutch) organs before the mid-1600's. We used only the high lead alloy in Opus 19, but listening to its plenum in Bach's music indicated that something was missing that apparently wasn't essential to Jan Pieterszoon Sweelinck's music. Besides the way in which they constituted their mixtures, the later masters differed from their predecessors in the composition of their principal choruses. In the time of Gottfried Fritzsche, Friedrich Stellwagen and Arp Schnitger, one seldom finds less than 20% tin alloys in their principal work, and, for reasons of prestige, front pipes von feinem Zinn, woll Aussgepolirt were always demanded when money was available. . .

The trend of using high lead seems to have been revived in the late 1970's, notably among the big American firms of Fisk, Taylor & Boody, Fritts, David Moore, Pasi and Bedient, who went to great efforts to research the technology applied by the Scherers, Fritzsches, Stellwagens, and later the Schnitgers and the Silbermanns. This coincided approximately with the time that the corroding grade lead became unavailable. This was not the reason that the “Return to the Old Masters" came about, but merely a coincidence. A lot of study went into early construction techniques and the results were rather interesting. It seems that when Charles Fisk was working on his Op 72 - the organ at Wellesley College - he came to the conclusion that metal that had been treated in the old manner (by hammering or such) and having thus been purposely "roughened" in density or thickness were by its very unevenness encouraging the development of a richer sound. Fisk felt that metal such as hammered lead, cast the way it was done in the 14th century, would actually be superior to rolled lead or zinc because of the different nature of the more “crudely” formed metal. He went to great lengths and considerable expense to make pipes according to the principles of construction of historical examples and, in my opinion, succeeded beyond his highest expectations.

What do we require of a successful pipe material?

The basic requirements are structural strength, stability and non-resonance. The sound produced by the pipe should not necessarily be affected by the material of which the pipe is made; i.e. the pipe body itself should not resonate, only the air within. There are those who say that a pipe's material has no effect on its sound, but numerous authorities I have known and respect have very clear opinions to the contrary. Body resonance often manifests itself as nasty buzzing sounds. There are certainly instances where the resonance of the pipe body is encouraged, but then it is allowed in the search of a particular timbre.

While there is nothing really wrong with trying new and different materials for pipemaking, there are several reasons for retaining the tried and tested methods and materials. Most modern materials such as zinc and rolled metals have one thing in common - their density is very even throughout - and this is where their chief “failing” lies. On grounds of strength, however, they are indeed far superior to the high-lead alloys.

Much research has been conducted recently into the metallurgy and casting of pipe metal by the Göteborg Organ Art Center at Göteborg University. It is certain that their work will go far to improve our understanding of this subject.

Over the centuries the major metals used in the construction of organ pipes have been the following:

Lead

Lead has been the standard material for organ pipes for a very long time. The reasons for this are partly because of its availability, cost, high density and softness and its ability to dampen unwanted resonance. However, because of the fact that modern lead is so pure and because of its low strength/weight ratio, it is particulary prone to creep. To compensate for this most pipemakers add the trace elements removed during refining back into the metal during casting. This generally consists of very small amounts of antimony, bismuth, copper and silver and, in rare cases, aluminium, iron and nickel.

Audsley (Vol II Chapter XXXV § 9 pp. 503-504) says:

“LEAD - In anything approaching a pure and unalloyed state lead is absolutely worthless for the construction of organ pipes. It has, nevertheless, been frequently used, stiffened and rendered brittle by the addition of some old type-metal or antimony...

“Lead is a very soft, heavy, and malleable metal of a bluish-gray colour. When freshly scraped or cut, it presents a lustrous surface, but this quickly becomes dull from the formation of a film of oxide. It cannot be polished or burnished on account of its extreme softness.”

Tin

While lead has had an almost universal application tin has often times been avoided almost completely. This is usually due to one overriding factor - cost. Nonetheless, apart from the instances where lead is particularly desirable (e.g. in the case of flutes etc.) tin has been considered the metal par excellence for strings, façades, principals and just about anything else. The French classical builders and the Silbermanns were probably the most famous people to employ tin in a wholesale manner, constructing most of their choruses with it.

Audsley (Vol II Chapter XXXV § 3 pp. 501-502) says:

“TIN - Of all the materials employed in the construction of metal pipes, English tin is unquestionably the best; and this fact has been recognized by all the great organ builders of the world. This metal closely resembles silver in colour, including the whiteness and luster and takes a polish almost equal to it, tarnishing very slightly under ordinary atmospheric conditions. It resists to a remarkable degree the action of impure air, generated by the breathing of large masses of people, and the corroding effects of the fumes sent off from burning gas, coals, etc.”

Zinc

Zinc has always been a metal of convenience only. There is not one instance that the writer knows of where zinc was employed prior to the nineteenth century. Even then it seems to have always been for reasons of economy or strength.

If we look at the types of alloys used by the differing schools over the ages we see the following:

Metal Properties, Structure and Ageing

Properties

Copper Zinc Silver Tin Antimony Lead Bismuth
Symbol Cu Zn Ag Sn Sb Pb Bi
Atomic number 29 30 47 50 51 82 83
Atomic weight (AMU) 63.546 63.390 107.880 118.700 121.760 207.200 208.980
Specific gravity (g/cm3) 8.69 7.04 10.46 7.36 6.70 11.35 9.79
Melting point ºC 1083.0 419.6 961.9 232.0 630.7 327.5 271.3
Melting point ºF 1981 787 1761 449 1169 621 520

Structure

To an extent whatever pipe material is used, the same tone partials (fundamental and harmonics) will be obtained due to the construction of the pipe. However, some materials lend themselves naturally to the enhancement of certain timbres and tones more readily than to others. For instance lead has the ability to generate solid fundamentals that in a chorus develop tremendous power and solidity. Nevertheless, if one chooses materials that are “bright” or “dark” and they significantly change the timbre, it has to be due to these interrelated but separate factors:

Modulus of Elasticity: This is what is commonly called stiffness. Generally a failure in this regard is manifested as creep.

Hysteresis: Hysteresis is easily described as internal friction and basically reduces resonance. For example, a cymbal (the percussion instrument) has very little hysteresis. It becomes quiet after its vibrating energy goes into the air to make sound waves.

Hardness: Harder materials vibrate more than soft materials. When materials reach their elastic limit they remain “altered” (basically they stay bent) because of their low strength.

What about alloys?

Lead alloys: Lead alloys are very soft, but strangely enough the very high percentage alloys are remarkably resistant to creep. The sound obtained from lead alloys is very fundamental, epitomized in the “dark” sounds of a true Posaune or German Praestant.

Spot alloys: The surface character of spotted metal is due to the molten lead and tin having different melting (or freezing) points. As the liquid alloy passes through its eutectic point and begins to solidify, the metals separate and crystallize as the melt solidifies in small regions on the casting table, thereby giving the finished sheet its spotted surface. The general theory is that the lead solidifies first, with the tin “encasing” it.

Tin alloys: The best way to describe the high tin alloys is thus “weightless shimmering light” (as opposed to “dark”). The elegance found in the work of the Silbermanns and the French epitomizes this.

Other alloys & trace metals: Some antimony makes lead/tin alloys very hard. A little aluminum will cause it to have severe and continuing grain growth. Moisture with any trace chemicals on the surface will create white powdery zinc oxide. These variations and compatibilities are true of lead and aluminum alloys as well. Copper, tin and silver alloys are less electro-active and more stable.

Zinc: So, what about zinc pipes? Some say they are tinny, some dull. The hardness varies widely because of metallurgy. Small amounts of other metals will make zinc very hard. Pure zinc is very soft. Very soft metals can dampen sound by hysteresis.

Ageing

It is a well-accepted fact that the structure of metal should alter through the years. Change in metal structure due to heat, rapid temperature change and vibration are well known and documented. Discontinuities in the crystal structure (known as dislocations) seem to move through the metal and combine with each other to form larger dislocations. This happens over a period of time and would certainly have an effect on the resonant properties of the material. Creep is probably the most apparent effect of ageing.

Metal Analysis & Composition

Most of the research into high-lead alloys was conducted during the late seventies and early eighties. Much of the work done more recently serves to confirm the outcomes of these experiments. Before the middle '80's when corroding lead became unavailable there were two available types: M.P. Möller used a substance during the 1930's called "Blue Metal". It looked like high lead content metal and had very high strength.

Techniques of analysis

Electron microprobe analysis is among the most successful of modern laboratory methods for determining the composition of metal pipes. The way it works is as follows:

An electron beam is fired at the sample, which is enclosed in a ultra-high vacuum chamber. These collisions cause the sample to emit electrons (called Auger electrons) and secondary ions. The electrons are analysed by Auger electron spectroscopy and the ions by secondary ion mass spectrometry. These spectrometric results provide “signatures” unique to the material being analysed.

An alternative method is to perform a “raster scan” with the electron beam by setting the beam energy to emit a specific chemical element. This obtains an image of the distribution of that element on the sample surface.

All these techniques are fairly surface-sensitive, meaning that they measure the chemical composition of the surface rather than the bulk. Many alloys exhibit a phenomenon called "surface segregation" where one component of the alloy preferentially migrates onto the surface.

In order to analyse the bulk of the metal, the layer of oxides on the surface needs to be removed by a process like argon-ion milling or mechanical scraping under vacuum. By analyzing the freshly milled surface one could get a fairly close approximation of the composition.

Tone Production

Before we discuss the differing compounds, let us briefly look at the physics of tone production.

Pipes don't vibrate, the air column within them does. Even with reed pipes, the resonator doesn't vibrate, but resonates. If the wall of the pipe were contributing to the sound, a simple test would be to blow a pipe supported only by the foot and then blow it supporting it farther up the wall. The timbre would be significantly different in each case. The resonator of a pipe does have the potential to vibrate, and voicers know that touching a speaking pipe does alter the sound.

Any change you may hear by doing this is due to the characteristics of the pipe material. This is the scientific theory. But in the real world, one finds that the timbre is not “totally” altered, just “noticeably” altered. Mainly it is the upper partials that are affected. It's not obvious and takes a good ear, but anyone who has worked around pipes of differing materials will agree to this. It's subtle, but there is usually a reason why pipes are made of certain materials in preference to others, despite cost. Voicers can get the sound they want from one material far easier than from another and that is why most of these decisions are made based on experience rather than “scientific” study. The explanation for one choice or another might be vague, but the result is due to careful planning.

Fisk and others spent many hours experimenting with pipemetal's effect on sound production. Fisk made round wooden pipes and square metal pipes. The main difference was the porousness of the wood. Wood pipes that were not glue sized exhibited a different sound quality. I have heard of these tests, but have conducted a few myself, and do not dispute the findings. I would like to point out that quite a few builders select thickness for pipe metal on more than just considerations for structural integrity. Stated differently, the deliberate and controlled manipulation of resonance of the pipe walls through the selection of alloy or wood and the thickness of such material is a technique the builder uses in the pursuit of a specific timbre. Yokota's description of his organ in The Historical Organ in America discusses this subject. In it he refers to Töpfer who claims a relationship between the wind pressure, pipe circumference, and wall thickness. Pipe bodies do not react the same way that tubular bells do for instance, but rather the air in it (which is a longitudal compressional standing wave) with a node approximately at the center and anti-nodes at the ends. Here the pipe acts as an open tube despite the presence of the foot. Pipes with bodies that are too thin will not contain the wave energy they produce at their mouths. Too thin, and the fundamental is killed. Too thick, and the harmonics are killed.

Tone production aside, lead pipes often must have thicker walls in order for them to be structurally sound.

Metal Composition (or “To Lead or Not to Lead”)

Alloys and their Treatment: In general the alloys behave such that the higher the tin content, the “brighter” the sound of the pipe, by virtue of increased resonance of upper harmonics. Lead is considered a “dead” metal. It does not resonate very well. The ratios of tin to lead have more to do with the metallurgy than anything else (all things being equal). Certain alloys are stronger and have a lesser tendency to creep.

Organ pipes with high tin content (about 50% to about 80%) are generally used for principals where one wishes to have many upper harmonics as possible. Pipes with approximately 1% to 50% tin are generally used for flutes and mutations where the large number of upper harmonics would actually detract from the timbre, either of the individual pipe, or the combination in which it is used.

Hammering is an antique process used to “toughen” the metal. This should not be confused with strengthening the metal which it does not do. Rather it closes any minuscule pinholes that the casting process may leave.

I have never heard a “real” reason for scraping other than it was done by the “old guys” for the purpose of evening the taper of the sheet.

Here are some recipes used by various builders:

80% Sn, 19% Pb, 1.1% Sb, 0.34% Cu, 80% Sn

(Used for Fisk Op. 91) C.B. Fisk comments: 2,000g Cu (shredded, melted with a rosebud tip acetylene torch) to 600,000g melt. A plumber's stove with a melting pot on top was used. Cu was added into pot and Sn (melted on buzzer stove) was added. The metals went into solution well, but the leftover pigs (cast from the leftover metal) contaminated subsequent castings, and had to be discarded. Later the pills were cast separately, and added to the pigs only in the pot. For non-corroding grade, 28.35g (1oz) Ag was added to 453,590g (1 000lbs) Pb melt.

Dom Bédos:
p. 177 § 862 — (adding Cu to Sn melt):
907.18g (2 lbs) Cu to 1,360-1,800g (3-4lbs) Sn
2.0% Cu is the most solution ever used - more likely 1.0-1.5% Cu.

p. 181 § 884 — he recommends 1.0% Cu to pure Sn.

1% Sn, 98% Pb, 1.0% Sb, 0.03% Cu

Wilhelmy (pp 30-31 § 9):

The alloy for high lead is quite similar for most builders: about 98% lead, 1.78% tin, 0.015% copper and antimony, silver and bismuth to share the remaining part. It is interesting that only two companies have their alloy prepared by a foundry; all the other alloy their metal in house. It might be worthwhile to “have it done elsewhere” - as one put it - so as to save time and irregularities and oxidation in the process. Industrial foundries can so crank up the heat and have their smelting pots enclosed while alloying that the results are often excellent, cheap, fast and available in large quantities. When commissioning a foundry we found it to be a good practice to have a sample of the new work analyzed by an independent metallurgical laboratory.
FJ Rodgers:
They use a 97% Sn, 3% Cu alloy specifically for tin case pipes.

Brombaugh:
The shop uses a 23% alloy for smaller pipes, especially cone-tuned ones. This particular alloy seems to be stiffer than the 98% Pb. However he does put solder seams on the mouth edges to strengthen them.

Metal “Diseases”

There is sometimes significant atomic migration in metals, in some cases even at room temperature. In some case (as with some gold alloys) the metals migrate to the surface; in others the foreign substances disappear into the bulk. Generally speaking, the softer the metal, the lower the temperature at which migration starts to happen.

Tin Plague (Zinnpest)

The Germans - at least in the far North - get zinnpest because it is so cold. Below a certain temperature the tin in pipes can break down into powder. This is the transition to “grey tin” (an allotrope) that occurs at low temperature, however it does not seem to occur in all circumstances. The example often quoted is that involving a shipment of tin ingots to the Russian government in payment for something that was stored in a cellar in St. Petersburg. By the Spring the tin had transformed into a pile of grey powder. The chemist they consulted showed them that by heating the grey powder it turned back into tin. This seems to be is practically unknown in heated churches. One thing to bear in mind is that true high-tin façades were a rarity until quite recently. Many of those “historic” tin principals in Northern Europe are not as old as the rest of the organ. Particularly in Germany the two World Wars ensured the demise of many tin façades where most of their surviving pipework is actually lead.

Tin Leprosy (Lèpre d'etain)

The French work is particularly susceptible to leprosy. This usually refers to the breakdown of pipe metal from casting on sand, impure alloys (perhaps containing iron or silicon) or from the use of something known as “fer blanc”. This condition seems to resemble that where pustules of corrosion form on the surface of the pipes and eventually corrode all the way through the material. Sometimes a powdery oxidation that is whitish in colour is observed.

Sugar of Lead (Lead acetate)

Pipe organs originating or situated in maritime climates are particularly prone to sugar of lead, usually showing up on cast lead reed blocks or high lead-alloy pipes. The Victorian English organs seem to be the worst affected. Sugar of lead or lead acetate (also known as Salt of Saturn) is a chemical compound appearing as a white (sometimes colourless), slowly efflorescent, monoclinic, powdery crystalline substance with a slight acetic odour and a sweetish taste that is, like other lead compounds, very poisonous. In the presence of extensive moisture it is formed as lead acetate trihydrate (Pb(C2H2O2)2·3H2O), also known as plumbous acetate or Goulard's powder. Lead acetate is soluble in water and in glycerin.

Metal Dangers

Lead is dangerous but must be ingested to cause harm. During casting, it is crucial to keep the temperature below about 800°F. Above that level the lead vapourises and can be inhaled. It can also be inhaled as dust, so high speed grinding or filing should be avoided.

Sources

Edwards L., ed. The Historical Organ in America Easthampton 1992 Westfield Centre
Audsley G.A. The Art of Organbuilding vols I & II New York 1905 Dodd, Mead & Co
Buckle S. The casting of pipe metal ISO Information No. 30 November 1989 pp 41-44
Fock G. Hamburg's role in Northern European Organbuilding Easthampton 1997 Westfield Centre
Lewis W.R. The Metallurgy of tin-lead alloys for organ pipes ISO Information No. 11 February 1974 pp 767-774
Robertson F.E. A Practical Treatise on Organbuilding Braintree 1897 (reprint) Organ Literature Foundation
Wilhelmy X. The Art of Casting High Lead Metal ISO Journal No 1 March 1998
Barnes J. & Renshaw M. The Life and Work of John Snetzler Menston (Yorkshire) 1994 Scolar Press
Bartholomew W.T. Acoustics of Music New York 1942 Prentice-Hall
Backus J. The Acoustical Foundations of Music New York 1977 WW Norton
Backus and Hundley Wall vibrations in organ pipes and their effect on the steady state tone quality Journal of the Acoustical Society of America, 39:936-945 (1966).