Could They or Couldn’t They?
Why the Glass on the 1 WTC Podium Won't
by Tara Taffera
One World Trade Center (WTC). It was supposed to be a jewel
rising from the dust of the former WTC towers. The architect envisioned
cladding the base of the building in light itself. Light refracted and
sent dancing by millions of prisms cut into the glass. Light that would
belie the dark history of what was once referred to as The Freedom Tower.
The world, and most especially the glass industry, watched eagerly as
the plans for this unique building unfolded.
And then suddenly, after years of preparation, it was announced in May
2011 that prismatic glass would not clad 1 WTC after all. The rainbows
could not be made. Or could they?
The decision has industry experts questioning whether those in charge—the
Port Authority of New York and New Jersey (PANYNJ), along with SOM architects
and Tishman Construction—made a wise decision when they collectively abandoned
the concept of prismatic glass (see June 2011 USGlass, page 12). Perhaps
the PANYNJ should have ceased its contract with the fabricator that reportedly
had problems creating the complex prismatic glass panels. The parties
involved may have had other options available to them that, until now,
have gone unreported. Is prismatic glass a viable solution for buildings
such as the WTC? Experts have differing opinions.
First, a definition of prismatic glass from a few who have worked with
the product. “Prismatic glass has been cut and highly polished to the
degree that it breaks white light into a full spectrum of colors,” says
Kenneth von Roenn Jr., president/director of design for Architectural
Glass Art Inc. in Louisville, Ky.
Nathan Munz, managing director of Glassform, an Australia-based fabricator,
believes there are various levels of definition for this term, depending
on the specifier’s design and performance requirements.
“The most basic [definition] would only require that the glass has facets,
which give it a number of surfaces at an angle to the plane of the glass
(as a prism has),” he explains.
|The Vision Unveiled, Before It Failed
Having a hard time visualizing the original design for the WTC podium
wall? Architect David Childs envisioned making the prismatic glass
come to life. In presenting his final design for the tower base in
June 2007, he described how the outside face would be made up of prisms.
“Some panels would have very big prisms and some would have small
prisms to give a fluctuation and a character to it. When sunlight
hits that prism it splays into color,” he said.
This is a very new idea about the base—one that we feel strongly about,”
said Childs, who added that the glass would be made of a laminated
safety glass—“so if it breaks for any reason it doesn’t fall in shards.”
to view the video.
A Quick Refresher
The original design for the podium wall of 1 WTC was to cover the concrete
base with prismatic glass (for the original investigative article detailing
the WTC construction, see April 2009 USGlass, page 30). According to the
SOM website, “The podium wall base is 186 feet tall and its cladding is
being designed to create a dynamic, shimmering surface that animates the
experience of the building at ground level” (for more on the original
design see the website in the box above).
The contract for the installation of the podium wall was awarded to Solera/DCM
Erectors, based in New York. DCM hired a subcontractor, Zetian Systems
Inc., based in Las Vegas, to perform design assist services, fabrication
and delivery. Zetian awarded PPG Industries, based in Pittsburgh, the
glass contract. PPG was to supply its Starphire ultra-clear, low-iron
glass to Zetian. Zetian, in turn, had contracted Sanxin Glass in Shenzhen,
China, to fabricate the Starphire glass into the prismatic panels. (For
more on Zetian and its role in the project, see May 2011 USGlass, page
But in May it seemed the plan fell apart. “As design moved to the testing
phase, it became clear that the prismatic glass simply had too many technical
problems to overcome and at a budget that was not cost-effective. We have
been finalizing a design that will be far more practical while being both
distinctive and magnificent,” John Kelly, a spokesman for the PANYNJ,
told The New York Times in May (The Port Authority would not return calls
The article also stated that the new façade is likely to be made
of more traditional clear glass panels, possibly with granite elements
to tie it into the surrounding plazas.
So it seems all of those parties above are out—unless they choose to bid
on the new design—and SOM is starting over. Elizabeth Kubany, public relations
representative for SOM, told USGlass in late August, “The client is reviewing
our designs and we expect them to select one for unveiling sometime in
the next few months.”
But some say the “technical problems” Kelly referenced with the prismatic
glass didn’t lay with the type of glass, but rather with the fabricator.
|Where Was the Mock-Up?
Several companies contacted for this article wondered whether or not
a full-scale mock-up of the 1 WTC podium wall had ever been produced.
“I’m surprised they didn’t say ‘let’s make a full-size mock-up’,”
says Bob Brown of Robert L Brown and Associates LLC. “A lot of times
with something unique like this they make some full-sized prototypes.
On very unusual jobs they do this pretty regularly.”
John Barber, former president of Barber Glass Industries Inc., says
when he was originally involved in development work for the project,
and when he was told by a senior partner of SOM that if he met the
price required he would receive a formal letter of intent, he developed
a full-size panel. The sample he produced was 44 by 156 inches, which
he says characterized the full panel which was to be 48 by 158 inches
“They never came to look at it,” says Barber. “I still have large
samples in my office. Most importantly, we never received the letter
SOM did not respond to USGlass’ questions regarding whether or not
a mock-up was produced.
PPG’s Rob Struble says he doesn’t know if a mock-up was produced,
but adds, “PPG recommends a mock-up on all commercial projects—it’s
part of our standard design guidelines. However, where PPG sits in
the contract chain, we can’t require it.”
Why It Won’t Work
Bob Brown of Robert L Brown and Associates LLC has been in the industry
for 51 years and is well-known as a tempering expert. The industry consultant
says he was contacted approximately a year ago by the “principals involved”
when “they were experiencing problems fabricating the glass.
“The problems they experienced were breakage and in laminating it,” Brown
says. “The panels were so deformed after tempering they couldn’t laminate
it.” He explains why, to his knowledge, it wouldn’t work—no matter the
Brown says the problem lies in taking 1-inch Starphire glass, in 160-
by 48-inch panels, and putting it on a flat surface and “machining it.”
In this case, the machining involves using an abrasive cutting device
to create some pattern on the surface of the glass. The thick glass is
also prone to spontaneous breakage during the tempering process, says
Brown, who adds that heat-strengthened 1-inch-thick glass would present
the same set of challenges.
“I have tempered 1-inch-thick glass,” says Brown. “The problem wasn’t
heating it; the problem was waiting long enough for it to cool. That has
to be closely controlled. If it cools too fast it gets too high of a stress
level. Almost anything would cause it to rupture.
“You have major problems in ensuring the temper is stable after the surface
deformation that occurs during and after tempering,” Brown continues.
“You also have problems in meeting the stress limits. Even if you had
the thin part of the glass meet those limits the thick part would exceed
And even if the thick glass didn’t rupture during tempering, machining
the glass would create a new set of problems.
“The machining would likely be done with industrial diamonds,” Brown says.
“They may also be polishing those grooves. When they cut deep grooves
they have created micro-fissures and the polishing is an attempt to minimize
the damage. That is what consultants will tell you is causing a weak spot
if you don’t get it nicely dressed around the cut. Those are micros-fissures
or flaws on edges or surfaces.”
But he has other misgivings as well.
“My concern is how to put that glass on any holding device,” Brown says.
“For holding or supporting the glass during the surface modification,
the table or frame in which it is placed must be very level and stable
[minimal flexure]. Large sheets of float glass weigh a great deal …. and
though rigid at normal temperatures, it will flex under its own weight
when not completely and fully supported. This would make machining the
exposed surface an inaccurate procedure. If the machining is intended
to create deep channels (grooves) in the glass surface, the variation
in such grooving could cause uneven depths of grooves and subsequently
cause a control problem for tempering in both the heating and cooling
cycles. Such problems would be exposed with breakage, bowing and poorly
Brown is not the only one who has concerns about the use of prismatic
glass on 1 WTC. Stanley Joehlin of the consulting company S.W. Joehlin
Inc. is highly regarded in the industry for his tempering expertise and
experience. In fact, he says, “Someone called me a few years ago when
[Sanxin] got into trouble [on this job] and I said I wasn’t interested
in going to China.” But he does have some thoughts on the prismatic glass
“Even if it would be possible to machine the glass and then polish the
surface, without micro-cracks (which is next to impossible), you may be
able to heat it uniformly if you left it in a very cool furnace,” says
Joehlin. “However the longer heating time required can be expected to
degrade the optical quality.”
“To temper a piece like that, I won’t say it can’t be done, but to uniformly
heat and cool and keep it flat is almost beyond present technology—unless
a company has a technique I am not aware of …. ”
Von Roenn Jr. agrees that the problem lies in the tempering.
“If someone can figure out how to temper it differently that would be
wonderful,” he says. “I don’t know enough to say if that was possible
or not. But when I first heard what they were trying to do [at 1 WTC]
I never thought they could temper it successfully. You can strengthen
the glass but you would never pass the necessary tests because the glass
wouldn’t shatter in small enough pieces.”
Like Brown, Von Roenn Jr. says machining offers another set of problems.
“There was no way they could ever have gotten a uniform tempering of the
glass with the process of polished V-grooves,” he says.
Alternative Number One
For each person who says prismatic glass this thick can’t be made there
are others who say emphatically that it can. At least two companies claim
they have developed a process in which prismatic glass could be fabricated
successfully. Both say they could have done it for 1 WTC—and both say
they were in talks with SOM and the PANYNJ while Sanxin was attempting
to fabricate the glass in China. One such company is a familiar name to
those following the story.
Canada’s Barber Glass Industries was the company named in the original
specification and spent millions in development work to create the prismatic
glass. (For more on Barber’s initial involvement, see April 2009 USGlass,
page 30.) It is important to note, however, that Barber Glass Industries’
fabrication arm is no more, as the 127-year-old company was placed into
receivership on November 10, 2010. Former president John Barber’s wife,
Susan, was successful in buying back the installation arm, and Barber
himself assists in the management of the company. He also serves as a
consultant for industry fabricators. Despite the widely known fact that
he lacked access to a fabrication plant, Barber says he received a call
in March 2011 from Nicole Driscoll at SOM who inquired again about Barber’s
ability to fabricate the glass. Barber says he even went so far as to
look for a plant and equipment to rent to fabricate the glass mock-ups.
Even before the call from Driscoll, Barber says he was aware that talks
about choosing an alternative supplier had started again. In March 2011,
Charles Flashburg of Johnson Screens told Barber that they were contacted
via the parties involved as well. In the early stages of development,
before the contract was awarded to Zetian, Barber was going to work with
Johnson Screens, which would have provided the back-up screen that would
hold the prismatic glass to the face of the building. (Johnson Screens
did not return requests for comment at press time.)
“Both my company and Johnson Screens had an excellent grasp of the requirements
and both had expended an excessive amount of capital to develop the product,”
Why did SOM come back to Barber, years after the contract was awarded
“I think the underlying reason is because I was only person with the complete
knowledge who was able to manufacture the prismatic glass to their requirements,”
In mid-2010, Barber fabricated prismatic glass with a similar profile
to the 1 WTC glass for installation on the Sperone Westwater Gallery in
New York City. Yes, the WTC is somewhat different, however the glass reacts
quite similar in the fabrication and the tempering of the product, Barber
“The WTC required very tight tolerances and a minimal amount of visual
support on the surface of the glass,” he says. “Sperone was a complete
frame section supported fully around the perimeter, and the WTC was a
frameless design. The large panels required for the WTC would be used
to cover the mechanical section of the building for the bottom 20 floors
and were purely decorative. Regardless of the size of the profile cut
into the surface of the panel the issues in the product are similar.”
Barber adds that the prismatic glass would pose an additional learning
curve in the 1 WTC installation because of the exposed edge, which would
require extra care in the product’s handling and installation. He pointed
out, however, that like any other product that is new on the market, it
requires time and effort to work out all the installation and handling
Barber was willing to produce several full-size mock-ups for the PANYNJ
as requested. He had proposed making four full-size panels and destroying
two of them to demonstrate how the glass would react if broken or over-stressed.
At that time, Barber gave SOM and the Port Authority a price of $796,000
to provide them with the required mock-ups.
“SOM was told not to continue its efforts on this design,” Barber says.
“I proposed that we could manufacture the prototypes in the timelines
they required with no issues,” he says. “PPG was willing to provide me
with the glass required. But let’s face it: With the current status of
my company I don’t have a whole lot of bargaining chips.”
SOM may have been willing to take a chance, but Barber speculates it was
the PANYNJ who “kiboshed” the idea. “I had lost my credibility in the
eyes of many,” he says. “But, I’m still one of the most knowledgeable
fabricators in the world.”
What about the concerns of consultants such as Brown regarding the tempering
“It all has to do with the tempering process,” agrees Barber “and [Sanxin]
hadn’t figured out the cooling process. It is not tempered under a regular
manufacturing process. At the end of the day we were able to temper it.
Under a normal 19-mil tempering recipe you would heat the glass for 15
minutes—this product was cooked for 45 minutes, then cooled very strategically.”
Barber adds, “That’s where the magic happened. The glass stayed red hot
for a period of time.”
Barber did create a full-sized panel early in 2009 during the initial
development work (see box above to the left) but adds that since that
time he had developed many improvements in the manufacturing of the product,
many of which were made during the manufacture of the Westwater project.
“We improved the way we fabricated the glass involving the use of water
to assist in the elimination of micro-fractures on the surface of the
glass,” Barber says. Brown says the use of water or coolants could minimize
the problem of micro-fissures or flaws on the edge of the glass.
“But it’s not just water—it’s the use of water along with the very sophisticated
machine tools and numerous equipment modifications,” Barber adds. “Micro-fractures
are a big issue in any fabrication of glass.”
The sun was streaming
through the window, hit the glass and it was like rainbows everywhere
and their jaws hit the floor. They loved it aesthetically, and it
would also work structurally.
—Nathan Munz, Glassform
Alternative Number Two
Barber is not alone in his belief that prismatic glass is a viable option.
Several time zones away in Australia, another fabricator, Glassform, was
perfecting a way to fabricate prismatic glass. The company was established
in 1985 and Munz has 35 years of experience in the glass industry.
Munz says that Glassform, along with Barber Glass, was named as an approved
fabricator for the prismatic glass in the original specification for the
“We were named in the original specification and a gentleman at Tishman
promised to put us in touch with the parties involved but we never heard
and we went on with our lives,” Munz says.
Things changed in May 2010 when Munz says he received a call from a representative
of Solera/DCM who was concerned about the Chinese fabricator’s inability
to supply the prismatic glass.
“From my knowledge of how the glass was going to be fabricated, I knew
there was no way that what they were doing would work,” Munz says.
But he was convinced his company could produce the glass, so he developed
a new approach to fabricating glass that would satisfy the aesthetic requirements
that architect David Childs had designed—including the ability to generate
“In order to produce the glass that was designed by Childs for 1 WTC,
we needed to produce a quality of flatness without ripples,” Munz says.
“The zigzag shape has to have a certain quality. Our sample shows our
glass is a true prismatic glass.”
To produce the sample Munz says he used PPG Starphire glass that he had
in his plant. He adds that Glassform’s solution for the prismatic glass
does not require 1-inch-thick glass to be used, so the sample used a thinner
PPG Starphire glass.
So how does Glassform’s method overcome the challenges pointed out by
“I learned that the Chinese were machining the glass with a peripheral
V-shaped wheel that will leave ripples on the glass surface,” Munz says.
“You cannot get a splay of color without very flat surfaces on the prism.”
He explains that the V is the shape of the edge of the wheel, which grinds
the surface to form the V in the glass, but that his method uses a different
type of wheel.
“The reason our prismatic glass has a surface finish that is flat and
without any ripples is indeed the method of machining used. I believe
that all other attempts involved machining the glass in a manner that
could never achieve the necessary finish to generate rainbows from sunlight—in
David Childs’ words, ‘splays of color.’”
In addition, Munz says Glassform’s design solution avoids the tempering
and laminating problems arising from other approaches, which are likely
to have prevented the successful fabrication of the final product.
Munz is keeping additional information about the product proprietary,
saying only that Glassform “figured out how to manufacture prismatic glass
panels with the aesthetic and structural properties necessary to satisfy
the requirements of SOM’s design for the 1 WTC façade.”
A Jaw-Dropping Meeting
Two months after the phone call from DCM/Solera, on July 23, 2010, Munz
traveled to New York City with a sample. Confident he could produce the
desired glass, he was ready to meet with representatives from Tishman,
SOM, DCM/Solera and the Port Authority—but the meeting never took place.
Munz wanted all the parties to sign a confidentiality agreement and says
only DCM/Solera would comply. So he went back to Australia, but didn’t
give up hope and went to work on another sample—this one 4 by 2 feet in
size. He flew back to New York City in October 2010 but this time, he
says, neither Tishman nor SOM would meet with him.
Munz says the project manager, Ken Lewis, eventually agreed to meet. Also
present, Munz says, were key members of the design team. Munz did not
request the signing of a confidentiality agreement at this meeting as
he had already submitted a patent application to the U.S. Patent and Trademark
“The sun was streaming through the window, hit the glass and it was like
rainbows everywhere and their jaws hit the floor,” Munz recalls. “They
loved it aesthetically, and it would also work structurally.”
Munz says he was asked to leave the sample so it could be shown to others
and he complied. “When I came back the following week to confirm a second
meeting as agreed at the end of the previous meeting they stone-walled,”
Munz says. “Subsequently a meeting with the design team was arranged on
the basis that it was not for the purposes of 1 WTC but to discuss potential
uses of the Glassform prismatic solution in other future SOM projects.”
And what about that sample? “It was shown to other SOM architects, and
the written feedback I received [privately] from one was, ‘This is the
best sample that has ever been produced for this installation. Everyone
I spoke to here agreed … Since this sample proved to be so beautiful,
it would seem that quite a few people are uncomfortable with how this
situation has evolved.’ ”
And at least one other person saw the Glassform solution as a valid one.
Leon Jacob, glass consultant with Jacob & Associates Pty. Ltd., based
in Sydney, Australia, says he was engaged as a consultant by the PANYNJ
to undertake specific tasks related to the prismatic glass façade
of 1 WTC.
“I am bound by confidentiality not to disclose details of my engagement,”
he says. “I can, however, comment that, after it became evident that the
contracted source of the prismatic glass panels was unable to supply,
I advised Tishman Construction and SOM Architects that I was aware of
the Glassform solution for the fabrication of the prismatic glass and
that I believed it was the only solution available which satisfied the
aesthetic and the structural requirements, and was able to be fabricated
Placing Blame,Money Wasted
Though Tishman Construction has remained relatively quiet on these issues
both Barber and Munz contend Tishman did not facilitate constructive communication
on the project.
“Tishman was controlling the process and blocked access at every point,”
Munz says. “They didn’t want Glassform’s prismatic glass considered and
they blocked access to the architect.”
“From day one there was resistance from Tishman that we did not understand,”
adds Barber. A representative from Tishman Construction declined to comment
on the story.
But some say there is plenty of blame to go around. When Munz learned
in early April 2011 that the Chinese were definitely out, he sent a letter
to Steve Plate, director of the 1 WTC Construction for the PANYNJ, and
summarized nine key points.
Among them was the fact that he traveled to New York in July 2010 to present
his solution together with samples. “The consensus at SOM was that the
sample viewed ‘was the best that has ever been produced for this installation,’
said the letter Munz sent to Plate. “SOM was scheduled to meet a second
time after a few days, but when this arrangement was to be confirmed,
they advised that they did not want to proceed with the second meeting.
It appears that a third party had instructed them not to consider any
proposal from Glassform.”
The letter, dated April 4, 2011, also stated: “It appears that the prismatic
concept for the 1 WTC podium façade is now being abandoned on the
grounds that it is not able to be supplied. This is simply untrue.”
According to Munz, when Plate received the letter he instructed a representative
of Tishman to call Munz on behalf of the Port Authority to say: “The owners
have decided to abandon the prismatic glass concept for the 1 WTC façade.”
Since the parties aren’t revealing why prismatic glass was abandoned many
have drawn their own conclusions—and most of those have to do with cost.
“My first guess is the cost concern,” Brown says. “I’m referring to Donald
Trump’s concept of going to China because ‘it’s cheaper there than it
is here’” (see November 2010 USGlass, page 42).
Ten million dollars had already been spent on the prismatic glass portion
of the project. PPG’s Rob Struble also confirms that PPG did produce the
specified Starphire glass, some of which was shipped to China and the
remainder of which is sitting in a warehouse.
“It is a shame they spent that much money without testing it first,” von
Consider Kelly’s earlier comment: “As design moved to the testing phase,
it became clear that the prismatic glass simply had too many technical
problems to overcome and at a budget that was not cost-effective.” But
Munz says he could have produced the glass cost-effectively.
“We can use any glass,” he says. “One of the differences in our approach
is we don’t need glass that runs thick. We could use ½-inch-thick
and that reduces costs.”
Barber can’t help but think what would have happened if the parties involved
had used his company as the original fabricator.
“They had their sights set on saving money,” says Barber. “I was told
$8 million was the number we had to sharpen our pencil on. So now two
years and millions of dollars later, we are left with a total redesign
and a stock of 1-inch glass that will never be used. How much did they
save? They put their trust in a company that could not make the product.”
“They can’t afford to have any more egg on their face,” Brown adds. “From
that standpoint, they can’t afford to do it.”
"To temper a piece
like that, I won’t say it can’t be done, but to uniformly heat and
cool and keep it flat is almost beyond present technology. Unless
a company has a technique I am not aware of …."
—Stanley Joehlin, glass consultant
What’s Next for Prismatic Glass?z
While it seems prismatic glass won’t be used on 1 WTC, will it be used
in similar projects in the future? Can fabricators overcome the technical
Brown gave a litany of reasons the prismatic glass wouldn’t work due to
tempering and machining problems. That being said, he sees one way the
prismatic glass could be a workable solution for future projects.
“If a company is using chemical tempering, then laminating, it could work,”
he says. “It would be a costly process and a patience-testing process,”
and one, he added, that only might possibly work over a cycle of multiple
While Joehlin doesn’t claim to be a chemical tempering expert, he says
chemical tempering doesn’t offer the right break patterns that are needed
to create a safety break pattern for prismatic glass.
“It’s the high central tension that is used to produce the break pattern,”
he says. “If you had a piece like that shatter in a storm I don’t know
how it would break.”
And if it did work he says there are other difficulties at play. “With
that variation in the thickness of the glass, I don’t know of anyone in
the world that has a chemically tempered tank close to the size that would
Barber says chemical tempering is not a good option.
“This process alters the molecular movement in the surface of glass,”
he says. “The chemical process can be easily destroyed, and would not
lend itself to this type of install. We entertained the idea right from
the beginning but once we investigated it further we never pursued it.”
Munz remains mum on whether or not he uses chemical tempering in his process.
“As I previously advised, we prefer not to publish details of our solution
at this time,” he says.
Others say they would have used a completely different solution.
“We would have laminated prismatic glass using a technique we have called
Prismalite,” von Roenne says. “This is a name we use to describe our technique
for laminating prismatic glass pieces to plate glass. It is typically
used for applications that have natural light so that the prisms break
up the light into spectral colors.”
While representatives of fabrication companies talk about how they “would
have done it,” Brown says he’s glad he didn’t have to attempt it.
“I’m sure glad I didn’t have to do it,” he says. “Someone [plural] overreached
in trying to make fully tempered panels of this shape and surface configuration.”
But Munz says he is absolutely certain this glass will be installed on
other buildings and he is now making large-scale samples. He also is talking
to architects in Australia to use the product on a smaller scale.
“Just a few architects are aware of it,” Munz says. “Early next year I
will have a supply available … There is no question in my mind we could
have supplied it to 1 WTC on time.
“Every time it goes up on a building people will say ‘that could have
been on 1 WTC,’” he says.
Jacob adds, “I think the concept was brilliant and it could have been
a magical building in terms of Childs’ approach and they could have had
Tara Taffera is a contributing editor for USGlass
magazine. She can be reached at firstname.lastname@example.org
or follow her on Twitter @dwmmag.
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