APT - Cast Pyrex Glass Block

Cast Pyrex Glass Block: Illuminating Its History and Conservation IssuesAuthor(s): MARY JABLONSKISource: APT Bulletin, Vol. 41, No. 2/3 (2010), pp. 37-45Published by: Association for Preservation Technology International (APT)Stable URL: http://www.jstor.org/stable/20749122 .Accessed: 17/08/2011 09:31

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Cast Pyrex Glass Block: Illuminating Its

History and Conservation Issues

MARY JABLONSKI

The term Pyrex glass usually brings

to mind cookware, but it was also

used as a building material that

today presents special conservation

problems.

In the beginning it seemed like a simple project. A glass screen that formed part of a sculpture, Wisdom with Sound and

Light located in Rockefeller Center in

Manhattan, needed to be conserved.

Very quickly complications ensued, and the project was expanded to include a second glass-screen sculpture, Youth

Leading Industry, at another location in Rockefeller Center. Major renovations were being undertaken in the building where Youth was located, and the con struction schedule necessitated the commencement and completion of the second project before the first.

Both glass screens were disassembled, conserved, and reinstalled. Youth had to be removed to allow for structural work

adjacent to the screen, and Wisdom was disassembled because it was thought

that the joint sealant was failing. The conservation of Youth was a fairly straightforward project. The conserva tion of Wisdom turned out to be a

project where wisdom was gained but

just not in the manner we had expected. The "we" in this case was a team that consisted of an objects-conservation firm that was the lead firm on the project,

Wilson Conservation; an architectural conservation firm, Jablonski Berkowitz Conservation (now Jablonski Building Conservation, Inc.); an engineering firm, John D. Nakrosis Jr.; and a contractor, Urban DC.

The client, Tishman Speyer, and the conservation team wanted to ensure that the sculptural glass screens were pro tected and conserved properly. The

project and its direction were affected by a variety of factors, including time con straints and a lack of information about the materials used to create this sculp ture. There was very little research on

twentieth-century building materials at the time, and that remains true today.1

This paper attempts to fill a gap in information regarding conserving archi tectural Pyrex cast-glass block. Much of the information that follows on the

materials and the creation of the two Rockefeller Center glass-sculpture screens was uncovered long after these two projects were completed. The paper concludes with a project that was begun in 2009, ten years after the completion of the work on Wisdom: lessons learned from the work on Wisdom informed a

more recent Pyrex cast-glass block

project, the lightbulb on the Thomas Edison Memorial Tower in Edison, New

Jersey.

A Brief History of Pyrex Glass

The most common form of glass and one of the oldest is soda-lime glass, also

37

Fig. 1. Wisdom with Sound and Light, 30 Rockefeller Center, New York, N.Y, in 2010. Photographs by the author, unless otherwise noted.

38 APT BULLETIN: JOURNAL OF PRESERVATION TECHNOLOGY / 41:2-3, 2010

' jBT^ I *^ _ ̂ JiS ^j!^^^ m IBs '

*5f ^Ma?Jr . ... -

i,.,i>M-^s^^M^^^r

Fig. 2. Plaster model for glass panel of l/\//SGfom w/'fh Sound and Light bemg prepared, c. 1932.

Frederick C. Carder Archives, Rakow Research

Library of the Corning Museum of Glass,

Corning, New York.

called soda-lime-silica glass and silica

glass. It is used for many common

materials, such as windowpanes, bot

tles, jars, and lightbulbs.2 This glass is made with silica, soda, and lime. Al

though soda-lime glass is a poor con ductor of heat, when it is rapidly heated or cooled, one surface changes tempera ture more rapidly than the other. This imbalance causes mechanical strains in the glass that result in cracking.

In the 1880s German chemists dis covered that by adding boric oxide to soda-lime glass a new glass was formed, borosilicate glass, which had a coeffi cient of thermal expansion that was less than half of that of soda-lime glass.3 This new glass was heat resistant and had low expansion characteristics and a

high degree of chemical resistance. Ini

tially the German chemists appear to have developed the glass for optical uses, but because of its thermal qualities it was quickly adapted for shades of gas lamps, thermometers, and laboratory equipment.4

While the German chemists were

working on this new glass, an American

company, Corning Glass Works, in

Corning, New York, was manufacturing lightbulb blanks, the glass envelopes for the lightbulb. Between 1889 and 1894

Corning was the sole manufacturer of these blanks for Thomas Edison's elec

trical company, but with the rise of com

petition in this field, Corning needed to

expand into new businesses. In the early 1900s Corning identified the expanding railroad industry as a potential con sumer for glass products. Lanterns were critical to railroads, yet the glass used in them was constantly breaking and re

quiring replacement. By 1908 Coming's research laboratory had modified the German borosilicate glass to create a

glass with low thermal expansion, which

they named Nonex, short for non

expansion glass. Corning subsequently became a major supplier of railroad lantern glass and battery-jar glass.5

Unfortunately for Corning, less

breakage of railroad lanterns meant a decrease in glass orders, and a new use had to be found for Nonex. In 1913

University of Michigan physics professor Jesse T. Littleton was hired to help solve this problem. His wife, Bessie Littleton, was instrumental in finding the solution. She thought the heat- and corrosion resistant glass would make good cook

ing vessels. Jesse Littleton brought home two Nonex battery jars with their tops sawn off, and Bessie baked a sponge cake in them. The trial was a success, and Bessie Littleton continued experi menting with Nonex.6

Bessie Littleton's experiments con

vinced Corning scientists that clear, durable borosilicate glass could be used to create new hygienic cookware. Corn

ing modified Nonex, which included

removing the lead in the glass, to create a new product they called Pyrex. In 1915 Pyrex baking dishes were success

fully launched on the market.

Developing Architectural Uses for

Pyrex Glass

Corning continued to experiment with its products, even as Pyrex glassware for cooking took off. One area of re search was in the field of architectural

glass. Corning had already been work

ing on strong glass, and this research, together with evolving construction uses for glass blocks and panels, suggested a new area for Pyrex development in the

early 1930s.7 A question of interest is why Corning

Glass Works began using Pyrex architec

turally as cast blocks. The process was labor intensive and by all accounts not

very profitable. Indeed, by the end of the 1930s Corning had joined with the

Pittsburgh Plate Glass Company to form a joint concern, Pittsburgh Corning Cor

poration, which manufactured hollow

glass blocks, a far more profitable enter

prise.8 All Pyrex blocks were either manufactured by Corning Glass Works or Pittsburgh Corning. Other companies produced glass blocks under other names. Perhaps cast-glass blocks were used because Frederick Carder, who was in charge of much of the design work in the architectural department at Corning Glass Works, was more comfortable with casting than with more modern fabrication methods for glass.

Frederick Carder (1863-1963) was an artist and glassmaker born in Eng land. He co-founded the Steuben Glass

Works in Corning, New York, with Thomas J. Hawkes in 1903. In 1918

Corning Glass Works bought Steuben Glass Works, leaving Carder to continue

managing Steuben. During the Great

Depression, Steuben became unprof itable, and it was reorganized. Carder

was made art director of the architec tural department at Corning Glass when it was formed in 1936. In this capacity,

Fig. 3. Completed glass panels of Wisdom with Sound and Light assembled at Corning Glass

Works for approval prior to shipment to Rocke feller Center for installation. Frederick C. Carder

Archives, Rakow Research Library of the Corn

ing Museum of Glass, Corning, New York.

CONSERVATION OF CAST PYREX GLASS BLOCK 39

Carder became actively involved in

designing architectural uses for Pyrex. Carder had been a terra-cotta sculp

tor early in his career, and this back

ground probably had an effect on how he decided to create the large glass panels at Rockefeller Center.9 Other workers at Coming's architectural glass department also appear to have worked in terra-cotta modeling. For example, a 1954 article in Gaffer', the Corning Glass Works magazine, reported on the career of Bill Gray during his 19 years in the architectural-finishing department.

He had started work at Corning in

1935, about the time that the last Rock efeller Center glass pieces were com

pleted. He had also created the plaster models for the Pyrex glass used in the

lightbulb on the Edison Memorial Tower. The article noted that Gray had been a terra-cotta plaster model maker

by trade that he had been a foreman at the terra-cotta company in Corning before he joined Corning Glass.10 A modeler sculpted the terra cotta and made the plaster model from which the terra-cotta molds were made, a process

very similar to the one Carder used to make his cast-glass blocks.

Almost all of the known architectural

Pyrex cast-glass installations fabricated

by Corning Glass Works appear to have been made between 1929 and 1938.11 Pieces larger than those mentioned in this article would have been made after

1933, when the Rockefeller Center glass screens were complete, as the accounts

of their manufacture suggest that much of the work was experimental. Other firms made glass blocks, but only Corn

ing Glass Works manufactured Pyrex cast-glass blocks.

Wisdom with Sound and Light was

probably the crowning achievement of the architectural department at Corning. Other architectural works were pro duced, but most were at a smaller scale, and it is probable that much of the

smaller, later work was designed by the Steuben department of the firm. Some of these works can be found in the c. 1935 Steuben architectural cast-glass catalog, which was geared to architects and de

signers and promoted not only standard

shapes for which the company already had molds but also its desire to work with clients to produce their own de

signs. "After the full scale detailed draw

ing has been approved by the architect, a full sized model is carefully con structed to follow the original design," the catalog stated. "We maintain a well

equipped department with expert mod

elers, especially trained in this class of work."12

According to this catalog, Steuben architectural cast glass was made in two basic types: Steuben crystal, which was the most expensive and could only be used for indoor pieces, and Pyrex glass, which was cheaper and was not "af fected by atmospheric conditions,"

making it ideal for the outdoor pieces.13 Cast-glass pieces were also offered in colors. Two green marbleized pieces can be found on the 1937 Canal Street Post Office in New York City, along with a

large cast-glass Pyrex screen.14

Deterioration Problems in Cast Pyrex Blocks

The deterioration problems of Pyrex have not been well researched, particu larly those involving architectural

Pyrex. There is little incentive. Cook ware that is sold as Pyrex is no longer made of borosilicate glass. Few people even know that Pyrex was used archi

tecturally, especially since it was used in a limited number of buildings.15

The deterioration problems found in the projects described here were spalls and cracks, in addition to soiling. It

appeared that many of the spalls could be the result of their installation. The

glass blocks are heavy, and it would have been easy for a worker to strike another glass unit while trying to ma neuver a block into place. None of the

spalls or cracks appeared to compromise the structural integrity of the units. The cracks found in the architectural instal lations were limited to a few units, and none appeared to run through the unit. Period accounts of the glass screens

suggest that each unit was very carefully checked prior to shipment from Corning Glass Works. There is also the possibil ity that the casting process produced flaws that were not detected by the

equipment available at the time of pro duction.16

Fig. 4. View from the back of Wisdom during dismantling, showing the vertical supports, the fasteners connecting the glass to the supports, and the V pattern of disassembly.

Lee Lawrie's Glass Screen for Rockefeller Center

One of the earliest uses of architectural

Pyrex glass was at Rockefeller Center. Construction began in 1930, in the middle of the Great Depression. A year later John D. Rockefeller Jr., who was

financing the project, set aside $1 mil lion for an art program.17 Sculptor Lee Lawrie contributed several pieces to the

project, one of which was Wisdom with Sound and Light, a bas-relief sculpture of molded- or cast-glass blocks and limestone at the center of the complex, above the entrance to the RCA Build

ing, now known as 30 Rockefeller Plaza. The glass portion of Wisdom is 15 high by 25 feet wide (Fig. 1). In her book on the art at Rockefeller Center, Christine Roussel called it "one of the most dramatic and technically difficult works in the Center, a massive multime dia piece created from a single slab of

carved, polychromed limestone and 240

cast-glass blocks.18

Lee Oscar Lawrie (1877-1963), a

prominent sculptor, worked on approxi mately 30 pieces of sculpture at Rocke feller Center, with the best known prob ably being the bronze Atlas at 636 Fifth Avenue between 50th and 51st streets.19 Lawrie began his career sculpting in a classical style, but by the time he began working at Rockefeller Center, his work had become much more abstract. In July 1933, soon after Wisdom was installed,


Fig. 5. Youth Leading Industry, 636 Fifth Av

enue, New York, N.Y., in 2010.

Pencil Points published an article enti tled "Glass, A New Sculptural Medi

um," which commented on how con

temporary the sculpture was:

The cosmos, or universe, is represented in the moulded glass of the portion of the screen

directly below this figure, and continues the

subject matter of the stone sculpture. This

sculptural glass panel represents a great stride forward both in the creation of abstract design and in the adaptation of glass to the highest type of architectural use, namely, the execution of detail for the principal focal point in the design of a monumental entrance. The architects of Rockefeller Center, Reinhard & Hofmeister; Corbett, Harrison & MacMurray; and Hood &

Fouihoux, and the sculpture Lee Lawrie, had the

daring vision of a glass panel entrance. The

producers of the glass, through the evolution of a new technique of manufacture, have success

fully translated the idea into a finished reality.20

It was not technically possible to make this screen from a single glass unit, so it was manufactured in sections. All blocks were uniform in height and

width, 18 inches high by 28 inches wide, but the thickness varied, with most ap proximately 3 inches, but others ranged from 472 inches to 1V4 inches. Accord

ing to the article in Pencil Points the

problem in thickness: was overcome by the adoption of a type of glass that hardly expands and contracts at all under even the widest range of temperature, a Pyrex glass the coefficient of linear expansion of which is only .0000032 for each degree of temperature

change between 19 degrees and 350 degrees centigrade. A special schedule of annealing procedure for the units of this screen was also

established and checked by means of an optical testing apparatus which reveals to the inspector even the slightest residual stress. Each of the blocks was subjected to this test.21

Forming the sculpture was a compli cated affair. Lawrie created a small-scale model in plaster of paris. Frederick

Carder, together with his assistant Paul V. Gardner and four laborers, made a full-scale model in clay, which was then cut into 240 sections that were then cast in plaster of paris (Fig. 2).22 Iron molds

were then made from the plaster models. The glass pieces were then cast and assembled in a mock-up for approval at the factory before they were shipped to

New York (Fig. 3).23 Since there were so many units and

the artist's intent was to have the screen read as a monolithic whole, the joints had to be as small as possible. The 1933 Pencil Points article noted that the "cement used must not only have a

strong adhesion to glass, be colorless and transparent, but must also have a refraction index approximately the same as that of the glass if the joints are not to be made unduly prominent. Vinylite, a synthetic resin, was chosen."24 The

Vinylite was made in thin strips to make the sealant almost invisible.

In addition, the artist did not want the steel framework holding the screen

together to be visible on the front. The blocks varied in weight from 70 to 115

pounds. To give the screen rigidity and to ensure that it could withstand wind

loads, vertical steel bars were placed at the vertical joints on the interior face of the sculpture. These steel supports were

painted gold to blend into the sculpture, and the steel fasteners that connected the glass to the vertical structural units were well concealed (Fig. 4).

Vinylite

Early sealants either were oil-based

putties or were made from naturally occurring bitumen or asphaltic materi als. Generally the oil-based putties were a form of calcium carbonate, such as

whiting or chalk, which was mixed with a drying oil, usually linseed oil. The oil based putties were particularly effective when used in conjunction with oil based paints, which bonded well and

protected them from the environment.

Still, the putties did not have a life

expectancy beyond 10 to 20 years.25

With the advent of World War I there was limited availability of linseed oil, which led to development of new sealants by the young polymer industry. Synthetic polymeric adhesives began to be used in place of the older vegetable-, animal-, and mineral-based joint seal

ers. The new products had stronger adhesion and greater formulation possi bilities, but the older materials contin ued to dominate the industry until well into the twentieth century.

The sealant used for Wisdom was

Vinylite, a product developed by the Union Carbide Corporation in 1927. What made Vinylite so attractive, apart from being colorless, was that it was a

promoted as an "elastic plastic": it could be made into products that stretched and then returned to their

original shape. Previously, plastics were

typically rigid materials.26 Since it could be made into a thin, elastic film with

good adhesion qualities, Vinylite ap peared the perfect invisible sealant for the new architectural glass material, Pyrex.

Youth Leading Industry

Two other cast-glass sculptures were created for Rockefeller Center. Only one remains, Youth Leading Industry, designed by Attilio Piccirilli, which was commissioned in 1936 (Fig. 5).27 The

sculpture, which was located on the International Building at 636 Fifth

Avenue, is 16 feet high and 10 feet wide and weighs three tons. Attilio Piccirilli

(1866-1945) was an Italian-American

sculptor largely known for his marble

sculptures. Piccirilli came to the United States in 1888 and worked for his father and then with the Piccirilli Broth ers as a sculptor, modeler, and stone carver at their studio in the Bronx.28

Using the same technique that was used for Wisdom, Youth was created in

plaster at full scale and then cut into the 45 units needed to create the glass molds. Notes from Frederick Carder's file indicate that there were extensive

problems with the molds. Apparently the architectural-glass department tried new techniques for making the molds. The first seven glass units were found to be cracked when they were extracted from the molds. A second attempt was no better than the first. Eventually, the


department appeared to find a method that worked, but Carder put at the end of his notes, "Glass came out with lots of white streaks."29

Whereas Lawrie had created his

sculpture using clear blocks, Piccirilli wanted a different effect, which Corning called "poetic glass." In The Art of Rockefeller Center, Christine Roussel

quotes a Corning publicity statement that explained that "the molten glass was poured in small quantities by hand in such a way to cause bubbles and striations which break up the glass's crystal clearness, giving it the effect of

fluidity and hand molding, and the

general appearance of a huge slab of

onyx."30 Great care was taken in ensur

ing that the edges were all carefully honed smooth and level.31 There were also publicity photographs showing the

honing of the blocks for the now-miss

ing companion sculpture. Vinylite was also reportedly used as a sealant for that

sculpture.

Dismantling and Reassembling Youth

Leading Industry

While the initial plan was commis sioned to conserve the glass screen of

Wisdom, major renovations undertaken at Rockefeller Center during this period necessitated the removal of Youth be fore Wisdom.

Before any work began, each block was labeled with a number and an arrow indicating its orientation. The conditions assessment noted that there was paint on areas of the exterior sur face and that there were a great many cracks in the glass blocks.32 The sealant

proved to be a recent silicone structural

caulk, installed when the sculpture had been conserved less than 10 years earlier. The current team thought that the cracks in the glass may have been the result of the method by which the glass had been made.33

Behind the sculpture was a glass screen that concealed the original back

lighting for the sculpture. This screen was made of Pyrex glass blocks that were either rubbed and frosted or smooth and clear; all were soiled but in

good condition. Like Wisdom, Youth was attached to and supported by steel vertical members that had some corro sion. Youth's steel supports were hidden

by the second screen and were cruder than those for Wisdom. It appeared that all of the large, cast-glass architectural

pieces were attached to and supported by vertical support members.

In order to disassemble the sculpture, the caulk between the glass blocks was cut using a thin wire.34 The joints were wide enough to pass a wire though them. Attaching a handle to either side of the wire allowed two workers to saw

through the joints. This method worked

fairly well for cutting all of the joints between the blocks. The only problem was the Plexiglas spacers between the blocks that broke the wire quite fre

quently. The sculpture was quickly disassem

bled, and the blocks were moved to a

workspace that had been set aside on the mezzanine of 30 Rockefeller Plaza for the conservation work. The conser vators then removed the remaining caulk fairly easily with razors and a 1:1 mix of ethanol and water. Care was taken to mask off the painted areas, and the glass was cleaned with Orvus WA Paste diluted 3 percent in distilled water

using cotton swabs and lint-free cotton cloths.35 The painted areas were cleaned

gently with soft bristle brushes and then with a 1:1 dilution of ethanol and water with cotton swabs. In-fill painting with

acrylic paint was done where there were

paint losses.

Structural work was quickly per formed at the building, and the sculp ture was reassembled. The Plexiglas spacers were reused, as was a Dow

silicone structural caulk that appeared to match the sealant found on the sculp ture. At the time it was not yet known that Vinylite had probably been used for the original joints.

The one alteration made to Youth in its as-found condition was to put a 74 inch glass gasket, Norton Tape, between the angle that supported the sculpture and the bottom glass-block units and between the glass and the vertical sup ports.36 It was believed that this would

protect the bottom of the glass blocks from staining and cushion any vibra tions.

Conditions Assessment of Wisdom

By 1999 the glass screen of Wisdom had become heavily soiled, and the in

Fig. 6. Drips of Vinylite on the face of Wisdom in 1999.

terior face of the glass had been covered with an anti-glare coating that created a frosted effect. It is not known when the

coating was applied, but it was in place by 1971.37 At the time work began, the

glass was so dirty that light barely passed through it, and pedestrians walking into or in front of the entrance

barely even noticed its existence.38 An additional problem was the Vinylite, the

original joint sealant. As with most

materials, Vinylite ages and deterio rates. It undergoes a deterioration pro cess known as dehydrochlorination, in which the hydrogen chloride is elimi nated from the polymer backbone and forms conjugated double bonds. This

process causes yellowing when exposed to daylight or ultraviolet light. Moisture can also cause the Vinylite to deterio rate chemically and physically by break

ing down; the physical manifestation is

typically swelling of the material. The

Vinylite on Wisdom had discolored and

dripped down the front and back face of the sculpture (Fig. 6). The drips were

unsightly, and there was concern that the sealant was failing.

The project began in May 1999 with limited research and a thorough condi tions assessment of the glass screen. Like

most projects, the client was interested in meeting a completion schedule. Since

Wisdom is the backdrop to the Rocke feller Center Christmas tree, the work had to be completed by the time the tree arrived at the beginning of November. Research was not to interfere with the schedule.

For the conditions assessment each block of glass was labeled with a num


Fig. 7. Dismantling Wisdom, using steam and a

linoleum knife to remove the Vinylite sealant.

ber and the orientation of the block. Information from these labels was then

placed on a key drawing. Small spalls were found on several of the blocks, with the largest spall found on a top corner unit. It was later concluded that this spall probably occurred during the

original installation. There were a few cracks in the units but nothing that

appeared structural, and certainly none extended through the Pyrex blocks.

As the conditions assessment pro ceeded, complications arose. The neces

sary permits, including one needed to dismantle the sculpture, had not been obtained from the New York City Land marks Commission. The second major complication was much more serious. The owner had sent a sample of the sealant for testing, and it showed a posi tive result for asbestos. While the as bestos problem was being dealt with, the team was working on Youth. After long, drawn-out dealings with a hazardous waste removal company, additional

testing of the sealant was undertaken, and no asbestos was found in the second set of tests.39 Work resumed on Wisdom in September 2009.

Conservation of Wisdom

As the glass screen of Wisdom was so

large, a sidewalk shed was constructed on both sides of the glass as protection

not only for the sculpture from the ele ments but also to protect anyone below. Most of the work was done after busi ness hours, as the entrance remained an

active one throughout the project. A

large unused room on the mezzanine was set aside by the client to perform any conservation work required for the units.

The sealant between the units had to be removed so the units could be dis mantled. This process proved to be one of the most challenging tasks of the

project. The method used on Youth did not work, as the joints were too thin to accommodate the wire. Many methods were tested, including solvents and heat in several forms, including soldering irons. All were completely ineffective at

removing or even loosening the Vinylite. Things became a bit tense. It was Sep tember, and the work had to be done by the first week of November.

Some members of the team were

opposed to using any water, as tradition

ally water was not used for conservation treatments on glass. This project oc curred at the time when conservators were only beginning to agree that glass was not a liquid, and most of the pub lished materials on the conservation of

glass dealt with archeological glass items or stained-glass windows, where there are issues with unstable glass. Other team members felt this was an outdoor

sculpture that had been subject to the harsh New York City environment, including acid rain, and water should not be an issue. Therefore, it was de cided to use elements that cause deterio ration of poly vinyl acetates: water and heat.

A Robby V3000 steam unit was

brought in to test the use of steam. It loosened the Vinylite. Finally there was a result, despite the fact the Vinylite remained difficult to remove. A linoleum knife with a curved tip was then tried to hook onto the softened Vinylite and pull it out of the joint (Fig. 7). Success, at least of a sort, was achieved. The team removed the first inch or so of Vinylite out but could get no further. Hardwood

wedges were added to the process (Fig. 8). The joint was steamed; then the much-softened Vinylite was pulled out of the joint with the linoleum knife; the

wedges were pushed into the joint; the

joint was steamed, and more Vinylite

removed; and the wedges pushed in fur ther. This process was repeated until the

joint finally opened, and we discovered a

surprise. While Youth had nice smooth

joint edges, Wisdom had interlocking joints.

Once the method for loosening the bond between the Vinylite and the glass was found, work progressed smoothly. The blocks were removed in a V pattern, since the knuckle connections between the blocks and the vertical steel supports dictated the pattern. Two people worked on each block, one on either side. Gla zier handles were used to lift the blocks and hold them as they were moved to the bottom level of the scaffold. There was only one accident, when a ladder

slipped. Luckily the two men lifting the unit were not hurt. The only damage was a spall to one unit. The client was

immediately notified that this would be fixed when the units were cleaned.

Thick plastic sheets were laid out on the floor of the unfinished space where the blocks were stored and worked on. A 240-unit grid was laid out on the

plastic, and each box was given a num ber that corresponded to the glass block that was to be stored there. This process

was important to ensure that the sculp ture was reinstalled the same way it was

Fig. 8. Dismantling Wisdom, using steam and wood wedges to help separate glass blocks.


Fig. 9. The Thomas Edison Memorial Tower,

Edison, N.J., being inspected in September 2009.

taken out and that it would be easy to find each block as it was needed.

Initially the sculpture was cleaned

using a 1:1 dilution of ethanol and water with lint-free cotton pads and cotton swabs. This process was far too

slow, and it became necessary to speed the process to finish on time. Robby steamers were used again, this time to remove the residues from the joints, the

soiling, and the anti-glare coating from the back of the units. The 1:1 dilution of ethanol and water was used for the

remaining cleaning. The steamers added a great deal of

humidity to the room. The humidity together with a lack of heat in the room created a problem when it came time to

try to fix spalls using epoxy fills. Conser

vation-grade epoxy was tried, but it would not cure in that environment, even with heat lamps. There was no other space in which to work, and in the end it was not possible to fill the spalls. A warm, dry room for the fill work was not a possibility for this project.

The final problem came at the re installation mock-up in the storage room. Because structural caulk had worked so well with Youth, it was as sumed that it would be used for Wis dom. The mock-up, however, made it obvious that it could not be used. Clear structural caulk is not clear. The joints showed opaque white against the clear,

amber-tinted glass, and it looked very bad. A quick search was undertaken to find a true clear caulk. One was found: CRL Water Clear Silicone Sealant manu factured by C. R. Lawrence Co., Inc.

Before reinstalling the glass blocks, the vertical supports were cleaned and loose paint removed, and they were

repainted with gold paint. Deteriorated felt had been located between the glass blocks and the metal supports, so felt was reinstalled in the same locations.

While Vinylite had been installed in

strips, the silicone sealant was applied in a bead. It was contained on the interior side with a clear 3/8-inch silicone tube

(SPX-50 Silicone tubing) that acted as a backer rod. Another bead of caulk was

placed on the interlocking V connection. Care had to be taken to ensure that bubbles did not form when the caulk was extruded. Each glass block was then lowered onto the previously caulked block. After installation, any open joints on the front and back of the sculpture were filled with the silicone caulk. The

project finished just in the nick of time, the morning the tree arrived.

Edison Memorial Tower Lightbulb

In 2009 there was another opportunity to work with architectural Pyrex glass, this time on a project with Farewell

Mills Gatsch Architects. Under the di rection of Anne Weber, lessons learned from Wisdom were applied to this new

project. Research time was included in the proposal for the work, as was test

ing of the sealant. The project began in

September 2009, and the restoration

design was completed in March 2010. The Thomas Alva Edison Memorial

Tower is located in Edison, New Jersey, on the site of Edison's earliest labora

tory. The monument is a large concrete tower topped by a 14-foot, 6,000 pound Pyrex glass element that represents an

incandescent lightbulb (Figs. 9 and 10), a major invention of Edison and his

laboratory. There are 153 Pyrex glass units forming jhe lightbulb. They vary in size from approximately 12 inches wide

by 18 inches high to 20 inches wide by 24 inches high. Each unit has raised, 2 inch diamond patterns on the exterior face and a smooth, frosted interior face. In addition, each unit is curved and has a depth of approximately 2 inches. The

lightbulb is supported on an interior ribbed-steel structure.40 Extra glass units that were found inside the tower pro vided the information about the depth and construction of the units (Fig. 11).

The glass units for the lightbulb were

designed and cast by the architectural division of the Corning Glass Works. This structure is possibly the first use of curved cast glass by Corning.

Bill Gray, a Corning employee in the architectural finishing department, created the plaster models that were used for the metal molds. Gray and his

boss, Walter Herriman, the head of the

department, then finished and assembled the units as a mock-up in the factory before they were shipped to Menlo Park.41

When the lightbulb was examined in

2009, the exterior of the glass units was soiled but appeared to be in good condi tion. At the side of each unit are two

square metal fasteners, believed to be

aluminum, which extended into the unit from the exterior and connected to the vertical steel-rib structure inside the

The interior face of the glass blocks is

frosted, which makes perfect sense when

standing inside the bulb on a bright and

sunny day, as the light is almost blind

ing. There was heavy soiling and biolog ical growth on the interior, partially due to a loss of sealant but also to an open ing in the copper at the top of the bulb.

Fig. 10. The Pyrex glass-block lightbulb on top of the Edison Memorial Tower.

bulb.


Fig. 11. Unused Pyrex glass units found inside

the Edison Memorial Tower. Author's photo graph.

There were five visibly cracked glass units on the north side of the bulb. None of the cracks appeared to extend

through the glass, and when touched, there was no evidence of any displace

ment of the glass at the crack. There

fore, it was assumed the cracks did not

compromise the integrity of the bulb. While several sealant campaigns are

visible, the original exterior sealant still remains in several joints. It does not ap pear that any interior sealant was used. Lead wool was used as a spacer between the glass blocks. The sealant color is a dark brownish gray, and testing identi fied the majority of the organic sealant material to be natural asphalt, possibly Gilsonite, which is also known as North American Asphaltum. As Gilsonite is a brittle material, this could explain the

friability of the sealant. There were also white fiber asbestos bundles that made

up approximately 9 percent of the

caulking material. The restoration plan included clean

ing the glass with Orvus WA Paste and a

solvent, probably acetone, as a de

greaser, particularly for the joints. The new sealant is a structural silicone caulk.

Lessons Learned

There were a number of lessons learned from working on the Rockefeller Center

project. One of the biggest was how

complex the decisions about conserva tion treatments can be. A second is that the lack of information on the materials

makes decisions more complicated, particularly for twentieth-century mate rials. As we all complete our projects, we must make an effort to publish what we have learned from our projects, what worked and, even more impor

tantly, what did not work. Also, we must gather information about the materials we find, which includes how

they were made and how they deterio rate. The better our information, the better our decisions will be.

MARY JABLONSKI is the owner of Jablonski Building Conservation, an architectural conser vation firm. She is also an adjunct professor in the historic preservation department at Columbia University. In her spare time she likes to research architectural materials and tech

nologies. She can be reached at mjablonski@ jbconservation.com.

Acknowledgments

I would very much like to thank two librarians, Gale Bardham at the Corning Museum of Glass and Kristine Gable at the Corning Corporate Archive. They were incredibly helpful in search

ing for the materials I needed and digging nug gets out of the files.

In addition to Jackie and Cameron Wilson, other people who contributed significantly to this

project were Elizabeth Moss and Ward Dennis, who worked for Jablonski Berkowitz Conserva

tion; Anthony Tiberia and John Nakrosis, from

John D. Nakrosis Jr., and Bob Schiffmocker from Urban DC.

Notes

1. Architect Thomas Jester made a good start with his book, Twentieth Century Building Materials, but published materials still remain limited at best. Other information exists on

glass block, but none of it on the cast glass that is discussed in this article. For more informa tion on glass block, particularly hollow glass block, see the chapter "Glass Block" in Twenti eth Century Building Materials and Elizabeth A. Patterson and Neal A. Vogel, "The Architec ture of Glass Block," Old House Journal 29, no. 1 (Jan.-Feb. 2001): 46-51.

2. Charles Bray, Dictionary of Glass: Materials and Techniques (Philadelphia: Univ. of Pennsyl vania Press, 1995), 206.

3. Heinz G. Pfaender, Schott Guide to Glass, 2nd ed. (London: Chapman 8c Hall, 1996), 24.

4. Werner Vogel, Glass Chemistry, 2nd rev. ed.

(Berlin and Heidelberg: Springer-Verlag and GmbH & Co. K, 1994), 19-21.

5. Davis Dyer and Daniel Gross, The Genera tions of Corning: The Life and Times of a Global Corporation (New York: Oxford Univ.

Press, 2001), 87, 95. Batteries were required for railway telegraph systems; these batteries

were made in glass jars that had to be acid resistant.

6. Dyer, 100.

7. Ibid., 257.

8. "New Pyrex Construction Unit," The Glass

Industry (Nov. 1935), 344; reference provided by the archives of the Corning Museum of Glass.

9. Thomas P. Dimitroff, Frederick Carder and Steuben Glass: American Classics (Atglen, Penn.: Schiffer Publishing, 1998), 93.

10. "Gray Retires; Helped Build Famous Bulb," Gaffer (Sept. 1954), n.p.; reference provided by the Rakow Research Library of the Corning

Museum of Corning Glass, Corning, N.Y.

11. Dimitroff, 103, uses the year 1935 for the

lightbulb, but it was cast in 1937 and installed on the tower in either late 1937 or 1938. The Canal Street Post Office, which has a Pyrex cast-block screen, was constructed in 1937.

12. Dimitroff, 90.

13. Ibid., 96.

14. The post office is located at 350 Canal Street and is an interesting Art Moderne build

ing designed by Alan Balch Mills and con structed in 1937. It has a large Pyrex cast screen in the center of the facade and two recessed light fixtures that are covered with ribbed cast glass, probably Pyrex, on either side.

15. The Johnson Wax Building, while built of

Pyrex, is made of glass tubing, not cast-glass blocks. It had its own set of deterioration

problems.

16. James E. Shelby, Introduction to Glass Science and Technology (Cambridge, UK: The

Royal Society of Chemistry, 1997), 189.

17. Christine Roussel, The Art of Rockefeller Center (New York: W. W. Norton & Co., 2006), 12.

18. Roussel, 85.

19. See www.louisvilleartdeco.com/feature/ LeeLawrie/LeeLawrie.html. This Web site contains a very informative article entitled

"Stalking Lawrie: American's Machine Age Michelangelo," by Gregory Paul Harm.

20. Eugene Clute, "Glass, A New Sculptural Medium," Pencil Points (July 1933): 306, reprinted for Corning Glass Works. The copy examined came from the Rakow Research

Library of the Corning Museum of Glass.

21. Ibid., 309.

22. "Glass Works Architectural Work Unique for Radio City," The [Corning] Leader, March

24, 1933; copy in Carder Archives, Box 2, The Rakow Research Library of the Corning Museum of Glass. Handwritten on the article, which was in Frederick Carders' file, is a note that reads: "I made the model 4 times the size of Lawries."

23. Paul V. Gardner, The Glass of Frederick Carder (New York: Crown Publishers, 1971), 121.

24. Ibid.

25. Michael J. Scheffler and James D. Connolly, History of Building Sealants: Science and Tech

nology of Building Seals, Sealants, Glazing and

Waterproofing, ed. Michael A. Lacasse (West Conshohocken, Penn.: ASTM, 1996).

26. See www.dhub.org/object/238241,vinyl +toys. The Web site of the Power House Mu


seum, which has a plastics collection, is Powerhousemuseum.com.

27. Davis, 257. Attilio Piccirilli's 1935 Labo

rata, located at the Palazzo d'ltalia (626 Fifth

Avenue, New York), was reputed to have been too Fascist in style and was removed during

World War II. Another version of the story states that Mussolini requested that it be re

moved, as it was offensive to Italians. It was

reportedly stored but has apparently been lost. This information was found in notes sent by the librarian at the Rakow Research Library of the Corning Museum of Glass. According to

Otto Hilbert, former Corning Glass Works

employee, "the large architectural glass with the man digging with a shovel was taken from Rockefeller Center after Mussolini visited the U.S. Mussolini was highly offended by the

image of the immigrant Italian as a common

laborer, and insisted that the work be removed."

28. Roussel, 311.

29. Handwritten notes labeled "Casting Win dows for Radio City Pickerilli, sculptor," File RCAGLASS/TXTLIB vlw - 3/96 The Rakow Library, Corning Museum of Glass.

30. Dyer, 261.

31. Roussel, 85.

32. There is no mention of paint being applied to the sculpture in any of the documents exam

ined during research on this paper. However, given the problems in making the blocks for this sculpture, the paint may have been used to

minimize some of the white streaks that Carder mentioned in his notes. The glass has a green tinge, and the paint matched the green tint of the glass very closely.

33. Several years later the conservator who had

initially conserved the sculpture told me how he had to use brute force to take the sculpture apart. While this may have contributed to an increase in cracks, it did not appear to have created any structural failure in the units.

34. The contractor's project manager, Bob

Schiffmocker, came up with this technique. The wire used was ordinary steel wire being used to tie items to the scaffold.

35. Orvus WA Paste is manufactured by Proc tor and Gamble.

36. At the time we did not know that felt had been used between the glass blocks of Wisdom and the steel angle and vertical supports. It is

probable that the original installation of Youth had used felt between the glass and the metal.

37. Gardner, 121.

38. On the day we finished and the scaffolding covering the sculpture was removed, several

people asked us when the new sculpture had been installed or told us they liked the new

sculpture.

39. For several months it looked as if the asbestos-removal company was going be dis

mantling the sculpture under the supervision of the conservators. They made a very minimal

attempt and decided they did not want to do the work.

40. Merrill Withington, The Edison Tower

(1938), 1. This pamphlet appears to have been handed out at the opening of the Edison Tower.

41. "Gray Retires; Helped Build Famous Bulb."

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