I had occasion to organize my thoughts on our manufacturing process recently, which over the past several years has evolved utterly without semblance of a plan. Since no one has manufactured copper cookware domestically for over a generation, it was never going to be the sort of path for which maps already existed. Not to mention that scaling hand-making to the level of hand-manufacturing is these days thought to be at least crazy, if not impossible. For example, Industrial development agencies, banks and various labor and building codes here in NYC actively militate against open-forge metal work at the scale needed to produce more than, say, a pan per day. That’s understandable – it’s dangerous work, there’s no training available for it, and space is tight here. So, our dramatic, urban-fire-code-unfriendly work is done further west in shops that have lots of room to breathe, by folks whose skills were passed down from previous generations of metal workers. This region is so steeped in such work it was known disparagingly as the “Rust Belt” until only recently. We like to think BCC is helping to reappropriate that term to a more positive association.
Here in über-creative Brooklyn we take care of the tamer, conventionally “creative” bits; design, marketing and administration – that sort of thing. Our process of creating a new pan blends design with respect for our materials and, literally, getting our hands dirty.
Giving shape to an idea.
How BCC goes about it is substantially different from how most manufacturers develop new designs these days. Barbara Stork has some 25 years experience designing castings. She may be one of the last designers of anything three-dimensional who neither knows nor wishes to know anything of computer-aided design. She draws all of our plans, elevations and designs by hand. Some of you may have noticed that the very first images we posted of our pans a few months back were her pastels – the first visuals we get of our wares all come from Barbara’s hand.
Pattern-making and tooling.
Once we all like the design, Barbara then models our curvy handles in clay and urethane to be sent to our tooling shop in Ft. Wayne, IN. There they are brought into the 21st century by laser-scanning the models in 3D to pilot a CNC milling machine, which produces the “match plate” tools we use in Plymouth, IN to cast our handles in ductile iron.
While that’s happening, mechanical drawings of the pan bodies are sent to our pattern shop in Dayton, OH where they’re used to mill a lathe mandrel – essentially a slab of steel sculpted to the interior volume of a pan. Our first lathe mandrel was a 250 pound 9.5” diameter behemoth which we’ve been using to make the bodies for our first sauté, rondeau, casserole and stocker. It’s tall enough to form any height pan body from the stocker on down, and is vented in several places to help release any height pan once it’s been tightly formed.
Our spinners are also in Dayton, and we teamed up with them specifically because they specialize in working with soft metal and still use manual lathes. While it’s entirely possible to program an automated lathe to “flop” soft copper over a mandrel repeatedly, what’s lost to that method is “work hardening”. We start with very malleable “electrolytic tough pitch” .125 (1/8” or 3mm) copper sheet and work it to what is known as “bell tuning”, the point at which the crystalline grain structure of the metal is organized in a less plastic, more elastic manner.
The skeleton of our pans is copper, whereas in the case of stainless steel-lined pans the hard, supportive structure is the steel lining. Stainless is nearly impossible to spin when clad, alloyed or press-bonded to other metals, so instead it’s deep-drawn on a press. When bonded to copper, as in Falk’s “Bimetal” process, the copper element starts very soft and highly plastic, and remains mostly so through the drawing process, allowing the pan to be formed without “fatiguing” or fracturing the crystalline bonds in the copper (which, according to Falk’s patent, has also been alloyed to further accommodate it to the stresses of deep drawing, harden it slightly in the drawing process, and to allow an interface alloy to form between the two layers).
So, because a tin lining contributes nothing to the structural integrity of a copper pan, we harden the copper. The process of work hardening is as old as soft metal spinning itself, but it requires the human ear, as well as a feel for feedback the metal delivers through the spinning tools. The progressive friction of a spinning wand, wheel or lever against copper slowly heats and enlarges crystal grain size, such that grains begin swapping atoms to meld into larger grains (loosely analogous to how proteins (gluten) join while kneading bread dough). As more grains aggregate the metal stiffens – granular dislocation becomes less likely as a function of decreasing granularity. Technically, this is less “hardening” (which increases energy resistance) than an increase in elasticity at the expense of plasticity – what we’re really doing is toughening the metal while preserving its thermal efficiency.
Spinning organizes a continuous and low granularity across the entire expanse of metal, which is where it departs from planishing (hammering), the effects of which amount to the toughening equivalent of spot treatments. Planishing generally leaves an irregularly distributed fine lattice of looser crystalline structure, but for all practical purposes the differences in performance and structural integrity between spun and planished copper are nugatory.
Bell-tuning is so-called because a lathe operator can hear it evolving as he moves metal up the mandrel. He is listening for the transition from dull rub-of-wand-against-copper to a resonant bell-like metallic pitch. His challenge is to get the metal formed over the mandrel at just about the moment the metal fully stiffens; if it does so before completing its formation into a pan body, it can “potato chip” (warp) or fracture as stress is applied in excess of the metal’s remaining plasticity. It will, in other words, become expensive scrap.
A successful spinning result is a tightly formed, toughened copper pan body that can now be drilled for riveting of its handle. That handle has been poured in its hundreds in Plymouth of a formulation of iron and carbon that crystallizes into ductile hardness that, unlike brittle gray iron, has a very high “coefficient of expansion” and elasticity similar to that of toughened copper. This ensures that the joint between handle and pan, and especially the rivets forming it, experience minimal friction (“fretting”) in normal use. We like when everybody gets along.
Rivets. No need to fret.
The rivets, being forged of the same “tough pitch” copper formulation as our pan bodies, are work hardened on the “shop head” when they’re made, and hardened again on the “bucked head” when they’re used to join our handles. What several millimeters of shaft connects through pan body and handle bearing plate remains soft and, when the bucked head is formed, expands to completely fill the cavity, affording more complete continuity of movement from one metal to another as well as protection against liquid penetration. Although it’s invisible to the naked eye, copper, tin and ductile iron expand and contract an extraordinary amount under normal heating and cooling, so any fretting inside the joint can, over decades, weaken the rivets. Using ductile iron and precise copper matching minimizes fretting and helps ensure our handles will be as firmly attached in 2216 as they are today.
To the tinning line.
Once we have a completed assembly of pan body and handle we move to the tinning line. The first step in lining our pans is a hydrochloric acid wash and “pickling”, which lightly etches the entire copper surface and removes a lot of superficial oxygen, which together bond the metals not only chemically, but also mechanically across three axes (“interdigitation” – imagine fingers locking). Exterior copper and iron surfaces are masked with lime paste so tin can be wiped into the interior without bonding anywhere we don’t want it.
The pan’s base is heated to between 1000 and 1200℉ so the entire interior temperature remains above the 425℉ melting point of pure tin long enough for the entire surface to be wiped by hand. Once the tin is thickly and evenly distributed the pan is immediately quenched to seize the tin’s crystalline structure within the etched copper and force a molecules-thin bronze alloy to form between distinct element layers, bonding evenly to both. This leaves a shiny tin interior, and a copper body that has been slightly annealed in the process. Upon completion of tinning and removal of masking, the visible copper in a pan is very well patinated.
Chaos, but only superficial.
Conventional dictionaries define patina as oxidation, but we understand oxidation more as corrosion – a process that produces by-products; in the case of corroded copper, carbonates, sulfates, sulfides and oxides. The truth about patina is more nuanced. We call patina the shift in color from the brilliant red-orange shine associated with new, polished copper to the less-reflective, brown/red-shifted finish of copper that has been used, but not yet oxidized. This color shift registers the action of heat in settling a copper surface from molecularly chaotic (counterintuitively, polished copper is extremely chaotic at the surface) to molecularly smooth.
Polishing compounds contain super-fine abrasives. These abrasives mechanically etch a surface to create microscopic prisms, which bounce and refract light at all frequencies and in all directions, registering to our eye as a mirror effect because we are able to see most of the visible frequencies of light in a polished surface. Owing to its native crystalline coloration, copper favors red-to-orange color shifts, but as a relatively soft metal it’s very easy to etch and therefore create the complex full-spectrum effects for which it’s famous. Indeed, the first mirrors made by humanity were polished copper.
Merely using a copper pan over heat causes it to lose its shine. What’s happening is the etched surface effects of a high polish are settling down to form more uniform crystalline structures (again, granularity is decreasing). In other words the metal is becoming microscopically more smooth with less superficial granular dislocation, resulting in fewer angles in which to bounce and break up light into distinct frequencies. Patina is a sign of increased thermal efficiency and surface toughness. Many professional chefs jealously guard their patination from the scullery line and polishing.
This also explains why commercial and other copper polishes work the way they do. Cream polishes contain light caustics such as ammonium chloride and citric acid, which gently etch the surface to create light effects similar to, though not as deep or complex as, what we get from mechanical polishing, which forms nice, even, parallel etching. When we polish we first “cut down” the copper surface, scoring it coarsely without removing metal, and then proceed through several steps of progressively crossing and recrossing finer and finer grades of scoring until reaching the “rouge” stage, where visible lines are mostly invisible and mirror effects are uniform.
Since every pan comes out of its spinning and tinning process slightly differently toughened, polishing time and compounding grades vary, each pan needing slightly different treatment. There are automated metal polishing techniques, but they tend not to work very well with copper.
After polishing, the ductile iron handles are wiped with food-grade butcher’s wax, a thin, penetrating coat that protects the handles from rust during shipping.
From our hands to yours.
To work copper to its best advantage takes a human touch with a proper respect for friction, heat and time. About a dozen-and-a-half hands care for your pan before yours do, guiding it through one trial and into the next, ensuring every step refines, strengthens and enhances. Copper’s reputation as an “intimate” metal is well-deserved – few materials transform quite so obviously for merely being handled.
In a way it’s even unsurprising that patina should further the mission of your cookware; as the darkening of time increases a pan’s utility measurably, to many eyes its beauty is likewise enhanced. Copper attracts us by revealing its wisdom and abilities as it ages. Like shadow, patina is the luster of the deep, beckoning energy into it. An excellent piece of cookware conducts heat as well as your creative energies.
At the end of our process the pan you receive is ready for your process, to begin a long history of making your dinner, of being known, of being included, of improving with age and of being loved.