This topic has generated a great deal of discussion, even controversy, among
phonograph collectors. Some claim that only tin-clad lead is authentic. Others argue
for pure tin, and some for pure lead. Unfortunately the subject is not quite so simple.
Research shows that there is no single standard for "original tinfoil" and logically we shouldn't expect there to be. Foil as a recording medium was subject to a great deal of variation, just as wax cylinders in the brown wax era. Edison did indeed buy tin-clad lead foil from J.J. Crooke of New York, who patented a process of laminating layers of tin to a core of lead. Unquestionably recordings were made on such laminated or clad foil -- a few samples still survive. However the composition of clad foil seems to have varied. Two reported lab tests show one with a tin content of 8%, another with 28%. But not all original recording foils were clad. Paul Israel, head of the Edison Papers Project at Rutgers University, believes that Sigmund Bergmann, Edison's associate who manufactured several tinfoil phonographs, made non-clad pure tinfoil in his shop. The Edison Speaking Phonograph Company, which controlled the rights to Edison's newly invented phonograph, advised its customers to buy foil directly from Bergmann, saying "The Record Foil especially manufactured for the Phonograph, may be had of S. Bergmann & Co." It was offered in wooden boxes of 5, 10, or 20 pounds at 45 cents per pound (about 30 sheets per pound). I have examined several samples of Bergmann-produced original foil, but without destructive testing there is no way to determine its metallic makeup. However, there are differences among the samples. One, found in an original box of foil (pictured on page 12 of Fabrizio & Paul's book "The Talking Machine"), measures 1.3 mils in thickness. The others measure 1.5 mils. Bergmann himself gave up on the tinfoil business in May 1880, saying "I have lost money on it all along and I have decided to turn over all orders to John J. Crooke...." It is also reasonable to assume that not all phonograph operators bought foil from Bergmann or Crooke. Tinfoil was readily available and there was no doubt an economic incentive to buying whatever commercial foil was at hand.
According to a very detailed article in the December, 1977 issue of Audio Age, the "oldest documented tinfoil sample" at the Edison National Historic Site measures 2.0 mils, and was reportedly made of tin-clad lead. I have been trying to find documentation for this claim but it seems that no one at the Edison Site today can corroborate it. There is ample documentation in Edison's papers for the use of 2.0 mil foil ("the thicker the better," Edison once wrote) and a recorded sheet of foil in the collection of the Henry Ford Museum, dated to 1878, is indeed 2.0 mils thick. However another recorded sheet in Ford's collection, recorded by Sarah Bernhardt in 1880 on a Bergmann exhibition phonograph, is 1.5 mils thick.
Further complicating the question, Paul Israel points out that by August 1878 Edward Johnson, President of the Edison Speaking Phonograph Company, wrote that Bergmann found "pure silver foil -- very thin -- costing less than 2 cents a sheet -- is as readily indented as tin foil" and had less surface noise. On October 22, 1878 Bergman announced that "After continued and expensive experiments to find some way of getting rid of the unpleasant ‘scratching' of the needle in the Phonograph, we have succeeded in producing a superior quality of foil, which almost entirely obviates that trouble. This foil we are now prepared to furnish in boxes containing 300 and 600 sheets, each @ one and five-eighths cents per sheet. Being of a different composition from that heretofore used, it can be used to advantage only on machines provided with the wedge fastening. Shellac, or other gums not readily adhering to it, it cannot be used on machines having that method of fastening. For these machines we will furnish the old style of foil at one and one-eighths cents per sheet, in packages of 170 and 420 sheets each."
Did this foil actually sell, and are any existing recordings in archives actually on silver foil rather than tin? Without destructive testing we will probably never know.
(Illustration from Harper's Monthly, March 30, 1878)
I have examined over a dozen surviving tinfoil recordings at the Smithsonian,
the Edison Site, the Henry Ford Museum, and in a few private collections. Some have
a much heavier feel than others, even when the thickness is the same. These are presumably
higher in lead content. Others handle exactly like pure tinfoil being manufactured
today. The thickness varies somewhat but the majority of existing foils are 1.5 thousands
thick, which seems to offer the ideal balance of recording quality and ease of handling.
The long and the short of it is that there is no single "correct" foil, but aluminum foil is very definitely not appropriate. Aluminum was an expensive metal in that era and aluminum foil did not become practical until the middle of the 20th century. Heavy-duty aluminum foil measures 1.0 mils in thickness, slightly less than the thinnest original tinfoil I've handled, but it is infinitely more rigid. The 1977 Audio Age article discusses the differences among metal foils: "The Modulus of Elasticity (Young's Modulus) is a measure of stress (in millions of psi) required for a unit strain (deformation) and can be used to describe the amount to which foil can be embossed. The Modulus number for tin is 6.5, for aluminum is 28.5, and for tin-clad-lead is approximately 3.5." Clearly the difference between tin-clad lead at 3.5 and tin at 6.5 is infinitely less than the difference between either of those foils and aluminum, at 28.5. You need only to handle tin foil versus aluminum to understand why aluminum causes so much more metallic rasping of the stylus against the foil than does tin. As for the difference between tin and tin-clad lead, Audio Age noted that the clad foil was very slightly superior in reducing surface noise, but that pure tin had "more clarity" than clad, and also that the sound impressions deteriorated less quickly in playback. They also noted that "both were definitely more distinct than aluminum."
In terms of performance, I have experimented with making recordings using several original tinfoil phonographs dating from 1878 to 1881, with 1.0, 1.5, 1.7, 2.0, and 3.0 mil thicknesses of pure tinfoil, as well as 0.5, 1.0 and 2.0 aluminum foil. I can only grade the results subjectively, but there were certainly differences. The flexibility of the thinnest tinfoil made it less easy to handle than the thicker foils, but it gave the loudest recording of the five tinfoils. My conclusion is that it takes less force to intent, so that the same level of loudness on recording makes a deeper impression on the foil, which then plays back with accordingly higher volume. The thickest foil was too heavy to handle easily and gave only fair reproduction. The intermediate thicknesses are perhaps the best compromise in that they combine comfortable weight with good recording qualities. Aluminum foil actually made for the loudest recording, but with by far the most surface noise, with 2.0 mil aluminum being almost unbearably noisy. (Wiping the surface of aluminum foil with a light coating of oil immediately prior to recording helps to reduce some of the metallic rasping.)
There is no doubt that tinfoil, or tin-clad lead, of anywhere between 1.0 and 2.0 mils falls within original parameters and gives vastly superior results than modern aluminum, with 1.5 mils being optimum.