The husband-and-wife team behind Borough Furnace share the process, from design to pouring the mold to spraying the enamel.

By Devorah Lev-Tov
March 02, 2021
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portrait of liz and john owners of borough furnace
Credit: courtesy of borough furnace

Cast iron Dutch ovens, pots with thick walls and tightly fitting lids, are stalwarts of the kitchen thanks to their ability to lock in moisture and retain a consistent heat for hours on end—plus, when properly cared for, they really can last forever. Use them to create tender and flavorful dishes like meat, stews, beans, and bread. A Dutch oven is also an ideal substitute for a slow cooker or deep fryer and the perfect tool for braising since you can sear food on the stovetop and then move the pot in the oven to finish cooking. But how is a cast iron Dutch oven made? Husband-and-wife team John Truex and Liz Seru of Borough Furnace tell us how they craft these extremely useful lidded pots in their workshop in the Finger Lakes region of New York.

First, a little background on Borough Furnace. After years of designing for furniture firms, John Truex decided he needed to be more hands-on. Rather than send his designs off for someone else to produce, he and Liz Seru started their own company in 2011. They design and produce cast iron cookware by hand, completely on their own. While the two had never made cookware before, they soon settled on a modest line including skillets and Dutch ovens. Truex studied metal casting and sculpture in school and Seru has an art background.

Ten years later, what started as a small workshop with homemade equipment has grown to include a new, separate building and state-of-the-art equipment in Owego, New York. They're currently switching over their equipment to all electric, with the goal of being completely solar powered in the next few years, and they recently branched into enameling, becoming the only company to do the labor-intensive process in the U.S. Still, Truex and Seru do everything themselves by hand—they have no other employees.

borough furnace 5.5qt Enameled dutch oven
Credit: courtesy of borough furnace

Design

It starts with the design, of course, and Borough Furnace's is sleek and functional, thanks to its lack of knobs. Truex did the designs himself, included making the lid and handle a single piece that can't break off (if you've ever had the knob of your pricey Dutch oven snap off, you know how convenient this feature is). The top, which uses a three-piece mold instead of a two-piece mold, makes it too expensive to produce for most other companies, but because Borough Furnace is a small shop, they can take the time to make it perfect.

"John is doing the design work so we can prototype everything in house and make tiny tweaks until it's right," says Seru. "Usually, you're hiring lots of outside shops or consultants and cost becomes a factor in the design, but we've managed to sidestep that."

The Furnace

Once they have a master pattern, they use it to create matchbook molds made out of sand. Sand is the only material you can pour molten iron into that can stand up to the heat without melting. And where does the iron come from? "We use recycled brake rotors because it's a high-quality cast iron," says Truex. "There's a recycling plant down the street from our shop and they'll pick up a ton of brake rotors with a big magnetic crane and drop it into the back of our truck."

Before they get to work with the furnace, they don aluminized Kevlar reflective silver suits, making the duo look like intrepid space explorers. While their original furnace that Truex built ran on recycled vegetable oil, now they use an induction furnace to melt down the rotors. "We put the metal inside a clay crucible in the middle of this induction coil and the magnetic field heats it up, getting hotter and hotter until it melts," says Truex. The new furnace holds 200 pounds at a time, which is enough for about 15 molds, either tops or bottoms. Once they pour the liquid metal into the matchbook mold, it solidifies in just a few seconds.

"It's kind of a process of pouring it in, you have to do it just right so that it doesn't go in too fast or too slow," says Truex. It took them about a year of practice before they became experts. Once the molds are poured, they let them cool overnight, breaking apart the sand molds the next morning. They use a special vibrating machine to return the molds back to sand grains to be reused in new molds. Next comes the hand finishing, which is done using belt and disc sanders to smooth the pot. Once the pot, which is a dark gray color at this point, is completely smooth, it either gets seasoned or enameled.

Seasoned Cast Iron or Enameled?

"For the seasoning, the process we use is something that people can easily recreate at home in case they need to re-season it," says Seru. "We use flaxseed oil, and it gets just hand rubbed on really thin and baked on in three rounds, until it gets a nice, deep black finish." Enameling is more complex, Truex and Seru have spent the last few years perfecting their enamel process, which they are now able to do on site. Enamel is a finely ground mixture of clay and glass that is mixed with water and then sprayed onto the pot, almost like the glaze on a ceramic pot. The duo retrofitted a spray line that they bought from an automotive parts supplier for about $25 in order to spray their pots. "The spray guns spray an even coating of the enamel slip, first on the inside of the pot," says Truex. "Then we do the handles by hand, to make sure there's a nice coating on the insides of the handles, and then we flip it over and spray the outside."

From there, it goes into a drying tunnel to remove all the water, leaving the shiny powdered enamel coating on the pot's surface. Finally, the Dutch oven goes into a kiln and gets fired at a little over 1400 degrees so the enamel fuses with the top surface of the iron, ensuring it won't chip. "What's so nice about enameled cast iron is that they are actually mechanically bonded together, it's not just like painting on top of something," says Truex.

New Projects

What's next for Borough Furnace? Aside from continuing to grow their enamel projects, they plan to make a special Dutch oven for baking bread with an inverted lid so that the flat slab can be put into the oven, and then turned upside down to create a steam chamber for the bread to bake in. It's clear Truex and Seru are skilled designers and metal and enamel workers, making top-quality cast iron cookware under the Borough Furnace flag. And now that we know how a Dutch oven is made, we have even more awe for the ingenious and timeless cooking tool.

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