Midnight Ride, Industrial Dawn

by Robert Martello

  Technical Experimentation and the “Secret” of Malleable Copper

  Revere launched his new career in May 1794 by contacting a government official (whose name is not recorded on the surviving letter) and discussing upcoming shipbuilding activity:

  I understand that there are to be two Ships built in this State, for the General government, and that they are to be Coppered, if so, they will want Composition bolts, Rudder braces, &c. &c.

  I can purchase several tons of Copper here, and my works are fitted for such business: Should those things be wanted, and I understand by General Jackson that it is in your department, if you will be kind enough to give me the refusal, you will much oblige me.

  I will do them as cheap as any one, and as well.65

  Revere’s networking abilities shine through this letter: he knew about the two ships soon to be under construction before work began, contacted General Henry Jackson and obtained more information plus the use of the general’s name as a contact, and fired off a letter to a government official (possibly Henry Knox or a purchasing agent) in order to lock up a contract. What this letter does not say is the fact that Revere had never produced a single bolt or spike or worked with pure copper on any large scale. As usual he had quite a learning curve to climb, but he confidently and correctly assumed he could master this new process.

  In future letters written long after finishing this first contract, Revere repeatedly refers to the magnitude of his technological achievement, for example, describing the “considerable labour & expense” he exerted when he learned to produce strong but non-brittle copper bolts and spikes.66 He offers even more detail in a revealing letter to Massachusetts Congressman Harrison G. Otis in 1800, in which he reflected upon some of his metallurgical successes:

  Before the Frigate Constitution and the other two Ships were built the new merchant ships that were to be coppered were bolted & spiked with cast composition metal (Copper & Tin) which from its being brittle, did not answer the end. When the Copper came from England for the Above Frigate by some Accident a part of the Bolts were too large, I was applyed to by Genral Jackson the Agent, to draw them smaller. I then found that it was necessary that Bolts & Spikes for Ship Building should be made out of Maleable Copper. After discoursing with a Number of Old Copper Smiths, they one & all agreed that they could not melt copper, and make it so malleable as to hammer it Hot. I farther found, that it was a Secret in Europe that lay in but very few Breasts.

  I determined if possible to gain the Secret. I have the satisfaction to say, that after a great many tryals and very considerable expense, I have so far attained my wishes, that I did supply the Constitution, for dove tails, staples, nails, &c &c to the amount of 1000 Weight drawn from Copper of my Melting. Since which, I manufactured for the Ships Boston and Essex, upwards of 10,000 weight of Copper into Bolts & Spikes, from Old Copper.67

  This letter lays out the context for Revere’s entry into this new field: his first commission asked him to modify existing bolts and spikes, an easier task than creating new ones from scratch. But when his inquiries among the local metallurgical community revealed the difficulty of this challenge and the complete lack of experience among all technical practitioners, Revere attacked it on his own via “a great many tryals and very considerable expense.” He described this process as a “secret,” hearkening to his artisan days, when he pledged to learn the “art and mystery” of his trade. Revere also repeatedly compared his product quality to that of British-made bolts and spikes; it went without saying that only an exemplary grade of copper could equal that of the British. Without any clues regarding his learning process, we might imagine that he probably practiced in his foundry until he could produce items similar to British ones. And while learning the secret of malleable copper manufacture, he also gained knowledge of a number of metallurgical principles that underlay these processes.

  The real challenge faced by Revere and other American metalworkers concerned the tradeoff between the different, and seemingly contradictory material properties that fasteners needed in order to survive the harsh conditions present in shipbuilding and ocean voyages. Metal fasteners often secured massive wooden beams to each other, and they had to resist being pulled apart or bent by the ship’s motion. Resistance to different stresses is a material property known as strength.68 But strength is most helpful in a material when it is combined with ductility, the ability to deform without breaking. Modern materials scientists describe the combination of strength and ductility as toughness, referring to a material that can absorb a huge amount of energy without rupturing. In other words, a tough material can resist most stresses applied to it (strength), and when extreme stresses finally begin to deform the material it bends without breaking (ductility). Tough metal led to more durable spikes and fasteners that enabled a ship to avoid frequent and costly overhauls and refitting, but contemporary practitioners could not express the product’s needs in this manner. Even with respect to iron, a metal used and understood far more than copper in Revere’s day, skilled workers did not fully comprehend the ramifications of their procedures or the different characteristics of metals. One industrial archaeologist contends that “Throughout most of the nineteenth century, mechanics thought that the stronger iron was, the better it was. They failed to appreciate the relationship between strength and toughness.”69 To make matters even more complicated, many fasteners received sharp impacts during the shipbuilding process as shipwrights hammered them into cured wood, requiring the additional property known as hardness to resist dents or deformations from blows. Many copperworkers initially attempted to make fasteners out of cast copper, a complete mistake. As with cast iron, cast copper is brittle and breaks or shatters under impact, possessing hardness but not ductility or toughness. The answer lay in an entirely different direction.

  By 1783, the British copperworking industry had developed a rolling process to produce “malleable” copper bolts and spikes, far stronger and less brittle than cast copper. The proper combination of cold-working, annealing, and hot-working produces fundamental changes in the microstructure of cast copper, successfully achieving the desired toughness. All metalworkers practiced cold-working when they changed the shape of copper or other metals through hammering or bending. Phrased in a more technical manner, cold-working produces plastic deformation, or a permanent physical alteration in the shape of the substance, such as bending a piece of iron into a horseshoe shape.70 Cold-working increases the amount of defects and strain within the metal, making it more brittle and less tough: for example, if a blacksmith bends a horseshoe too many times it will snap into two pieces. Britain’s real discovery came about when metalworkers combined the standard process of cold-working with annealing and hot-working, in order to mitigate the brittleness problem. Annealing is the process of heating metal without melting it in order to rearrange its atoms into a more perfect structure with fewer defects. This releases some of the metal’s strain and brittleness, and thereby restores its ductility and toughness. This process requires careful judgment on the part of the worker: insufficient heating fails to remove the brittleness, while excessive heating, or even prolonged heating at the proper temperature, removes the metal’s strength and makes it soft. Hot-working is the procedure of reshaping a metal after first heating it to the temperature range that restores ductility. Skilled coppersmiths fabricated malleable copper by a combination of hot-and cold-working processes, alternately heating, cooling, and hammering the copper until producing the desired blend of qualities. In this manner, copper could become both hard and tough, or in other words, simultaneously resistant to penetration, resistant to breaking, and non-brittle.71

  Two tasks faced Revere: he had to understand at least the rudimentary theory behind this procedure and he had to learn how to implement it. In correspondence throughout the remainder of his life he correctly uses terms (albeit with creative spellings) such as annealing, malleability, hard, tough, and brittle. He understood some of these concepts from earlier proj
ects dating back to his silverwork and he probably picked up new terminology during his many visits to different metal shops, but malleable copper forging gave him the chance to synthesize and direct all his knowledge toward a single goal. One clue hinting at the actual technical processes developed by Revere lies in his use of the word draw when describing his copper bolt and spike production process. As a part of his earlier silversmith training Revere gained plenty of familiarity with the wire-drawing process. Wire drawing closely approximated several nuances of malleable copper working: too little heating did not restore flexibility to silver wire, and too much heating softened or even melted it. He could not make copper bolts or spikes the way he made silver wire, by pulling them through a series of small apertures, but his silverworking experiences did teach him the concept of working metal to the point of maximum strain before heating it just enough to remove the strain, and then working it some more.

  Revere also learned a related technical skill during this period. In a January 1800 letter he mentioned that he used his furnace to refine 1,800 pounds of copper at a time.72 As noted earlier, copper refining was an extremely complex technology when done properly. Different copper ores could easily become contaminated with other chemicals such as sulfur or oxygen, and British refineries carried out a many-stage process that used different techniques to gradually remove larger and larger quantities of contaminants. Revere almost certainly did not possess the knowledge or equipment to carry out such a difficult operation but he might have imperfectly refined the metal by heating it in a reducing (i.e., oxygen-lacking) environment, which removed oxygen from copper. He might have also used the term refine to refer to the separation of copper from other metals in a mixed batch of “old” copper that often included tin, zinc, iron, and other materials. In this case he carefully adjusted the furnace temperature in order to liquefy metals with lower melting points and physically separate them from higher-melting-point substances. Although Revere lacked the ability to properly refine copper, any partial step toward this technology represented a landmark in post-Revolutionary America. Revere’s bolt and spike “drawing” process, therefore, probably involved a combination of refining cast or “old” copper into a purer state, forming it into bar shapes, and hammering and annealing it to produce the desired proportions and material properties. As always, he failed to commit any of his metalworking knowledge to paper, instead letting his products do the talking. Sales soon followed.

  Revere exhibited his growing metallurgical knowledge in an October 28, 1795 letter to Portsmouth Naval Agent Jacob Sheaf. Revere told Sheaf that he had just delivered fifteen tons of copper bolts to naval agent General Jackson. In his letter to Sheaf, Revere proved that he understood the technical nuances of this work: “should they [copper bolts] be cast, they will not answer for the use they came for, for when that metal is cast in sand, it looses a very great part of its Mallibility Malleable Mallebility and is very easily broken. But those which are drawn retain their Mallebility and are as tough as iron.”73 This advice proved timely because Sheaf planned to reduce the size of his own spikes by casting them, a move that certainly produced brittle products. Revere also singled out “casting in sand” as part of the problem. In another letter, written on February 7, 1796, to an unknown recipient, he uses metallurgical terminology with confidence: “Now Sir, any person who is aquainted with the nature of metals must know, that if it will stand the force of a Trip Hammer, after it is drawn to the size & swaged smoth, it must be tougher than at first, because the grain of the metal is finer.”74 Even though Revere may not have used the term tougher precisely in its modern form, he still shows a concern and awareness of material properties, made all the more impressive by his discussion of metal grain size, revealing a casual understanding of the correlation between a material’s microstructure and its properties. During his malleable copper research period Revere learned to produce quality output, but also strove to understand why metals behave the way they do. This scientific approach set him apart from the majority of practicing artisans and captured the love of learning that guided him through so many metallurgical adventures.

  Revere initially had unrealistic expectations regarding his products. In the February 7, 1796 letter cited above he claimed his bolts “acted under the hammer as tough as Iron,” adding, “I will risque my reputation, that you shall take one of those bolts and place it across two blocks of Iron and strike with a large Blacksmith sledge, backwards and forwards, three hundred times, before you can break them, and yet they are left Hammer hard.”75 This is a bet Revere could not win. He chose this imagery to demonstrate his bolts’ toughness, but even though many contracts attest to the quality of his products, infrequent customer complaints reveal that his bolts were not indestructible.

  Revere wrote another letter to Jacob Sheafe on January 7, 1799, in order to defend his spikes and reject a request to take back a shipment. Sheafe reported that he could not use the 616 pounds of composition spikes Revere recently sent him because workers cut the heads too large and left one side uneven. Even though he and his workers had to turn out many tons of bolts and spikes for each contract, Revere had not truly mastered the precision manufacturing and quality control methods needed for true interchangeability. His two-part response reveals much about his view of his products. Concerning the issue of the spike heads and unevenness, Revere noted “that all the English ones have large heads & the French ones have still larger & ar square,” the only direct response Revere made to the charge that his spike heads were too large. He did not discuss their unevenness at all. Instead, Revere used this letter to defend the workmanship and quality of his spikes in general, and to discuss the different types of metal used in spikes. He took a didactic historical and scientific approach to the subject:

  I wish to mention, when the Brittish Nation first began to [word missing] other than Iron bolts & spikes into their Ships, they were made of a composition of Copper & Tin, but they soon found that it would not Answer, by reason it was too brittle. They then found they could harden copper; they now make use of no Composition Bolts or Spikes, but clear copper.—If you wish to distinguish between Copper & Composition bolts or spikes, lay them across two pieces of Iron, bend them backwards & forwards, & you will soon find which breaks first, then look at the grain.76

  Revere also pointed out that Sheafe erred in describing the spikes as “composition” metal, since he sent only spikes made from “clear copper, drawn from barrs of copper under the hammer in the same manner as iron spikes are made.” In Revere’s terminology, “composition” copper referred to bronze alloys whereas “clear,” “pure,” or “malleable” copper referred to homogeneous copper. He added that Sheafe’s spikes exactly resembled the 1,500 pounds of spikes he had recently sold to the USS Constitution, and “The work men that drove them [the spikes] told me they were equal to the English ones. And what is more no man but my self in the four New England States, can melt the Copper & draw it in to spikes but my self.” The bolts were also “such as the Sec’y for the Naval department ordered to be drove into every Vessell building for the United States.” Revere frequently resorted to this tactic of defending a specific item or product by citing his body of work and overall experience.77

  Revere wrote a second letter to Sheafe on February 13 and did a better job of addressing the actual topic. In this letter, Revere admitted that he rushed this shipment of spikes to ensure they all arrived in one package. Therefore, “some of them might not be quite so even as others & their heads a little larger.” He devoted the majority of his letter to the charge that his bolts were too soft to penetrate the hull of a ship. This time, he contended that some woods, particularly the prized live oak used on certain naval vessels, were hard enough to break even British spikes. The shipbuilders of the Constitution had a similar problem, and overcame it by boring holes before driving each spike. In conclusion, Revere mentioned that he could draw the spikes to a smaller size for $5 per one hundred spikes, and make them strong enough to drive
“near as well as iron.”78 Even though Sheafe clearly had a problem with this shipment of spikes, Revere’s offer to draw them down, as well as his helpful advice about pre-drilling the hull before using the spikes, presented several helpful solutions.

  Although Revere held his technical prowess in high esteem, his self-praise carried a large element of truth. His achievement was, without question, a milestone for America. In his previously mentioned letter to Harrison G. Otis in March 1800, Revere presented a “Short History of that valuable & necessary Metal in this Country,” a history of American copperworking that suspiciously resembled a history of his own copper experiences. This letter confirms some of Revere’s statements concerning the rarity of copperworking knowledge in America: “[Colonel Joshua Humphreys] asured Mr. Stoddard that there were no person in America that could make Copper maleable so that it could be drawn in to Bolts & Spikes. I have shewn him, and he acknowledges that He was mistaken and gave me leave to make use of His Name.”79 If an expert as qualified as Colonel Joshua Humphreys, the nation’s most gifted naval architect, believed that no American possessed the knowledge and experience required to make malleable copper bolts and spikes, Revere’s achievement truly separated him from most if not all American metalworkers. Long after dismissing Revere’s claims, Humphreys had the opportunity to visit Revere’s shop, at which time he observed Revere’s advanced copper processes and products and immediately admitted his error. Humphreys’ retraction may have boosted Revere’s ego in the short term, but this powerful recommendation would have even larger long-term impacts, to be discussed in the following chapter.

  Revere’s malleable copperworking accomplishments soon elicited public praise. An article titled “The Launch,” printed in the May 21, 1799 issue of the Massachusetts Mercury, pointed out that the frigate Boston was the first ship exclusively constructed from bolts and spikes manufactured in the United States: “We think the publick are under obligation to PAUL REVERE, Esq., for his indefatigable attention to this Branch of Naval Architecture, especially at a time when the British Government has prohibited the exportation of that valuable Article.”80 This public use of “Esquire,” a gentleman’s title, surely had a powerful effect upon Revere. Many Americans recognized the importance of Revere’s accomplishment even though he duplicated, rather than invented, an existing British process. Being first was not as important as staying in the race.