Preserving Boston’s Historic Architecture : The Making of a Historic Iron Fence

Black iron fences are a staple in landmarked districts like the Back Bay and the South End, but their history and significance can often be overlooked, as well as the amount of work it takes to fabricate and restore them.  

The Times spoke with Peter Cassidy of metalwork company Cassidy Bros. Forge, Inc., who said that there is iron work of all types in Boston, but the two biggest being cast iron and wrought iron. “A lot of historic projects have a combination of wrought iron and cast iron,” he said.

After the Civil War, extensive amounts of cast iron became common, Cassidy said, but when it was first used on a production scale, it was known as “poor man’s wrought iron.” With cast iron, all of the artistry goes into making the mold at the foundry. This mass production offers “a lot fo great detail and ornamentation for very little effort,” he said, whereas wrought iron work is done by hand and is a much more lengthy process.

In districts like the Back Bay and the South End, people wishing to restore or replace an existing iron fence must go through the Back Bay Architectural Commission or the South End Landmarks District Commission, respectively. The purpose of these Commissions is to preserve the historic character of these neighborhoods and make sure any work done in the public way adheres to guidelines set forth by the district.

“Existing historic iron fences should be retained and maintained. If they are deteriorated beyond repair they should be replaced in-kind,” Joe Cornish, Director of Design Review for the Boston Landmarks Commission, told the Sun. If a historic fence is non-existent, he suggested looking for historic images at the South End Historical Society, backbayhouses.org, Historic New England, the Bostonian Society, Digital Commonwealth, and the City Archives.

“If the design of the historic fence is unknown then it will be important to find an appropriate black iron design that is appropriate for the scale and design of the building and that compliments the character of the district,” Cornish said.

Applicants for fence replacement or restoration work with their landmarks commission as well as companies like Cassidy Bros. Forge when figuring out what work needs to be done. After the design/restoration is agreed upon and approved by the Commission, it’s time to craft the fence and/or pieces that will be remade.

When Cassidy Bros. Forge makes a wrought iron fence for a client, they must first go to a foundry for cast iron. Here, iron is melted in crucibles and poured into sand molds to make the different parts of the fence.

To recreate a piece of fence that is too worn to be repaired, the piece of fence that is to be recreated is taken to a pattern maker, Cassidy said. The pattern maker will make an impression of the artwork that will be cast, and then it will be delivered to the foundry as a board with half an imprint on it. The imprint will be packed into a container called a flask and filled with dry, good quality sand then two flasks will be put together, Cassidy said. This creates a sand mold for that particular piece of the fence.

The molds are then brought over to where molten iron gets poured into them, the sand will fall away and the parts pulled out of the mold. They will then grind off any flashing, blast them, and deliver them to a business like Cassidy Bros. Forge, who will carry out the next steps.

The next steps are what Cassidy calls “fabrication mode,” as the foundry will make the parts of the fence but does not put them together.

“We will take raw casting and maybe drill holes, weld, take panels and blast them and prep them for paint,” Cassidy said, depending on the type of fence to be fabricated. Then, they will take the fence pieces to the site, drill into the concrete and finish assembling and installing the fence onsite.

“Cast iron is brittle like glass,” he said—“not a great material.” Over time, it breaks and pieces fall off. In order to restore a historic fence, “you have to make copies and save enough of the historic material that you can make a copy of it,” Cassidy said. “You want to look at the product and find the best pieces to make copies from.”

Once it is determined which pieces will be remade, they must be cut and taken to the pattern maker, who knows to cast the molds larger so the pieces come out to be the same size. Cassidy said pattern makers have special rulers that compensate for the shrinkage that happens when cast iron is made. There is 1/8 inch per foot of shrinkage, Cassidy said.

“We try to replace only pieces that are missing or extremely corroded,” Cassidy said, and fill in and grind smooth pieces that only have minimal corrosion. “Some pieces are not touched, others are retouched, and others are replaced,” he said of historic fences. “We are not trying to cover up the age, we’re trying to save it and preserve it and replace the missing pieces.”

Cassidy said that Cassidy Bros. Forge restores fences in the same way they were originally fabricated. “A lot of wroght iron fences back 100 years ago, they would drill holes and put rivets in them, collar, mortise and tenant joint,” he said. “If you’re doing a high quality restoration,” the new pieces of fence will be installed in the same fasion—“no gloppy, ugly welds.” The pieces will be extracted and  riveted together in the historic fashion.

Another important component of the restoration process is lead abatement and new paint. “In Boston, early paint had lead primer,” as it helped prevent corrosion, Cassidy said. It was usually a layer underneath the paint color. He said that if red paint is seen under a fence today, that usually means that it has lead in it.

In order to do a fence restoration up to today’s standards, a lead abatement must be done. This consists of blasting the metal down to a bare white seal, which must be done in an isolated and contained environment. Cassidy said that Cassidy Bros. Forge uses a company that blasts away historic material in a safe way and can provide documentation that the lead was disposed of properly.

Once the lead is removed, a new coating can be applied, but it must be done so immediately after it is blasted so the coating will adhere to the metal appropriately. Cassidy said that enamel paint can be applied, but it does not have a long life expectancy (3-5 years), and will need to be regularly maintained. So a two part epoxy primer and polyurethane coating is applied by Cassidy Bros. Forge instead , which has a 20-30 year life expectancy and “holds up pretty well outdoors.”

Another, more expensive option, is to galvanize the metal, which means it is covered with molten zinc. This gives it 60-100 years of rust protection, Cassidy said.

Cassidy said it is important to maintain iron work, as there is a lot in Boston that has not been properly maintained. “People keep looking at the rust for decades before anyone does anything about it,” he said. “We try to tell people how important it is after the first six months to a year to go back and examine and treat cracks and rust while they’re small.”

A lot of time, effort, and different hands go into creating and restoring the historic iron fences of Back Bay and the South End, and though many are unique, they are all subject to the guidelines of the landmarks commissions to preserve the beauty and integrity of Boston’s historic neighborhoods.