1

33 PRESERVATION

BRIEFS

The Preservation and Repair of 

Historic Stained and Leaded Glass

Neal A. Vogel and Rolf Achilles

National Park Service

U.S. Department of the Interior

Heritage Preservation Services

“Stained glass” can mean colored, painted or enameled glass, 

or glass tinted with true glass “stains.” In this Brief the 

term refers to both colored and painted glass. “Leaded glass” 

refers generically to all glass assemblies held in place by lead, 

copper, or zinc cames. Because the construction, protection, 

and repair techniques of leaded glass units are similar, 

whether the glass itself is colored or clear, “stained glass” and 

“leaded glass” are used interchangeably throughout the text. 

Glass is a highly versatile medium. In its molten 

state, it can be spun, blown, rolled, cast in any shape, 

and given any color. Once cooled, it can be polished, 

beveled, chipped, etched, engraved, or painted. Of 

all the decorative eff ects possible with glass, however, 

none is more impressive than “stained glass.” Since 

the days of ancient Rome, stained glass in windows 

and other building elements has shaped and colored 

light in infi nite ways. 

Stained and leaded glass can be found throughout 

America in a dazzling variety of colors, patt erns, and 

textures (Fig. 1). It appears in windows, doors, ceilings, 

fanlights, sidelights, light fi xtures, and other glazed 

features found in historic buildings (Fig. 2). It appears in 

all building types and architectural styles—embellishing 

the light in a great cathedral, or adding a touch of 

decoration to the smallest rowhouse or bungalow. A 

number of notable churches, large mansions, civic 

buildings, and other prominent buildings boast 

windows or ceilings by LaFarge, Tiff any, Connick, or 

one of many other, lesser-known, American masters, 

but stained or leaded glass also appears as a prominent 

feature in great numbers of modest houses built between 

the Civil War and the Great Depression.

This Brief gives a short history of stained and leaded 

glass in America. It also surveys basic preservation 

and documentation issues facing owners of buildings 

with leaded glass. It addresses common causes of 

deterioration and presents repair, restoration, and 

protection options. It does not off er detailed advice 

on specifi c work treatments. Glass is one of the most 

durable, yet fragile building materials. While stained 

glass windows can last for centuries, as the great 

cathedrals of Europe att est, they can be instantly 

destroyed by vandals or by careless workmen. Extreme 

care must therefore be exercised, even in the most 

minor work. For this reason, virtually all repair or 

restoration work undertaken on stained and leaded 

glass must be done by professionals, whether the 

feature is a magnifi cent stained glass window or a clear, 

leaded glass storefront transom. Before undertaking 

any repair work, building owners or project managers 

should screen studios carefully, check references, inspect 

other projects, and require duplicate documentation 

of any work so that full records can be maintained. 

Consultants should be employed on major projects.

Figure 1. This door and transom suggest the richness of 19th 

century leaded glass. Photo: Jack E. Boucher, HABS.
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Historical Background

Glassblowers were among the founders of Jamestown in 

1607, and early glass manufacturing was also att empted 

in 17th-century Boston and Philadelphia. Dutch 

colonists in the New Netherlands enjoyed painted oval 

or circular medallions that bore the family’s coat of arms 

or illustrated Dutch proverbs. German colonists in the 

mid-Atlantic region also began early glass ventures. 

Despite the availability of good natural ingredients, 

each of these early American glassmakers eventually 

failed due to production and managerial diffi culties. 

As a result, colonists imported most of their glass from 

England throughout the 17th and 18th centuries.

Social values as well as high costs also restricted the 

use of stained and other ornamental glass. This was 

particularly true with regard to churches. The Puritans, 

who sett led New England, rejected the religious imagery 

of the Church of England, and built simple, unadorned 

churches with clear glass windows. Less than 1% of 

the Nation’s stained and leaded glass predates 1700. 

Considering the enormous loss of 17th-, 18th-, and early 

19th-century buildings, any window glass surviving 

from these periods is very signifi cant (Fig. 3). Every 

eff ort should be made to document and preserve it.

Despite many failed starts, the War of 1812, and 

British competition, American glass production 

increased steadily throughout the 19th century. 

Stained glass was available on a very limited basis in 

America during the fi rst quarter of the 19th century, 

but American stained glass did not really emerge 

in its own right until the 1840s. The windows at 

St. Ann and the Holy Trinity Episcopal Church in 

Brooklyn, New York, made by John and William 

Jay Bolton between 1843 and 1848, are perhaps 

the most signifi cant early American stained glass 

installation (Fig. 4). Other important early stained 

glass commissions were the glass ceilings produced 

by the J. & G. H. Gibson Company of Philadelphia for 

the House and Senate chambers of the United States 

Capitol in 1859.

America’s glass industry boomed during the second 

half of the 19th century. (And although stained and 

leaded glass is found nationwide, the manufacturing 

was based in the Northeast and Midwest, where 

Figure 2. Components of a leaded glass window. good natural ingredients for glass, and coal reserves 

Figure 3. The entrance to the Morris-Jumel Mansion, New York 

City, is one of the earliest surviving installations of stained glass 

in the country. It features a fanlight and sidelights of large clear 

roundels and small bulls-eyes of red and orange glass tinted with 

silver stains from ca. 1810. Photo: Ken Moss.

Anatomy of a 

Leaded Window
3

for the kilns were available. Moreover, nearly all of 

the nationally renowned studios were based in major 

metropolitan areas of the central and northeastern 

states--near the manufacturers that supplied their raw 

materials.) In response to this growth, the industry 

formed self-regulating associations that established 

guidelines for business and production. In 1879 

the Window Glass Association of America was 

established, and in 1903 The National Ornamental Glass 

Manufacturers’ Association, precursor of the Stained 

Glass Association in America, was formed.

The 60 years from about 1870 to 1930 were the high 

point for stained glass in the U.S. In the early years, 

American stylistic demands refl ected those current 

in Europe, including various historic revivals, and 

aesthetic and geometric patt erns. American patt erns 

prevailed thereaft er; they tended to be more vivid, 

brash, and bold (Fig. 5).

Aft er the 1893 Columbia World’s Exposition, the Art 

Nouveau Style became the rage for windows. Sinuous 

nymphs, leggy maidens, whiplashed curves, lilies, and 

brambles became standard subjects until World War 

Among the leading proponents of the Art Nouveau 

Style were glassmakers John LaFarge and Louis Comfort 

Tiff any. Both men experimented independently 

throughout the 1870s to develop opalescent glass, which 

LaFarge was fi rst to incorporate into his windows. 

Tiff any became the bett er-known, due in part to his 

prolifi c output. 

He att racted world-class artists and innovative 

glassmakers to his studio. Today, “Tiff any” remains a 

household name. His favorite and most popular scenes 

were naturalistic images of fl owers, colorful peacocks 

and cockatiels, and landscapes at sunrise and sunset 

(Fig. 6). LaFarge, while appreciated in his own day, 

gradually slid into relative obscurity, from which he has 

emerged in recent decades. Tiff any and LaFarge are the 

greatest names in American stained glass. 

Figure 4. The windows at St. Ann and the Holy Trinity Episcopal 

Church, Brooklyn, New York, were made between 1843-1849 by John 

and William Jay Bolton. Photo: Leland A. Cook.

Figure 5. Stained glass is an exterior feature as well as an interior 

one. As part of any preservation project, stained glass should be 

photographed from the exterior as well as the interior. 

In dramatic contrast to the American Art Nouveau style 

was the Neo-Gothic movement that became so popular 

for church and university architecture across the country. 

Charles J. Connick was a leading designer of medievalstyle windows characteristic of the style (Fig. 7).

Advocates of the Prairie Style, of whom Frank Lloyd 

Wright is the best known, rejected Tiff any’s naturalistic 

scenes and Connick’s Gothic imitations. (Fig. 8). 

Wright’s rectilinear organic abstractions developed 

simultaneously with the similar aesthetic of the various 

European Secessionists. The creation of this style was 

aided by the development of zinc and copper cames 

in 1893. These cames—much stiff er than lead—made 

it possible to carry out the linear designs of Prairie 

School windows with fewer support bars. At fi rst, these 

windows had only an elitist following, but they were 

soon widely accepted and proliferated during the early 

20th century. 

By 1900, stained and leaded glass was being massproduced and was available to almost everyone. 

Leading home journals touted leaded glass windows for 

domestic use, and a nationwide building boom created 

an unprecedented demand for stained and leaded art 

glass windows, door panels, and transoms. Mail order 

catalogs from sash and blind companies appeared, 

I. 
4

some off ering over 100 low-cost, mass produced designs 

(although the same catalogs assured buyers that their 

leaded glass was “made to order”) (Fig. 9). 

The fading popularity of the ornate Victorian styles, 

combined with inferior materials used for mass 

production, essentially eliminated the production 

of quality leaded glass. The last mail order catalogs 

featuring stained glass were published in the mid-1920s, 

and tastes changed to the point that the 1926 House 

Beautiful Building Annual declared: “the crude stained 

glass windows in many of the Mansard-roof mansions 

of the ‘eighties [1880s] prove how dreadful glass can be 

when wrongly used.” 

Some creative eff orts expanded leaded glass media in new 

directions. Lead-overlay or “silhouett e” glass was one 

novelty that climaxed in the late 1920s and early 1930s. 

Some designers sandwiched glass between layers of handcut sheet lead, while others sandwiched the perforated 

sheet lead between layers of glass. These windows 

present a playful reversal from traditional stained glass; 

in “silhouett e” glass the lead metalwork, rather than the 

glass, becomes the primary art form (Fig. 10). However, 

such novelties failed to catch on during the Depression. 

World War II delivered the fi nal blow and ornamental 

glass is seldom found in residential, commercial, and 

secular architecture aft er circa 1940. The great age of 

American stained glass was over. Fortunately, leaded 

glass panels survived in uncounted numbers throughout 

the country, and are now once again appreciated as 

virtually irreplaceable features of historic buildings.

Figure 6. This 1907 landscape window is typical of those produced 

by Tiff any Studios. Characteristics include the use of opalescent 

glass, intricate leading and organic copper foil work, acid-etching, 

plating (i.e., several layers of glass), and a sense of perspective. 

Figure 8. This 1902 window by Henry Webster Tomlinson 

refl ects the Prairie School philosophy of providing 

ornamentation while retaining a view through the window. 

Figure 7. Charles J. Connick was another American master of 

stained glass. He worked in a modernized Neo-Gothic style. This 

window is from 1921. Photo: Diana Kincaid.
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Dating and Documenting Historic 

Leaded Glass 

Before deciding on any treatment for historic leaded 

glass, every eff ort should be made to understand—and 

to record—its history and composition. Documentation 

is strongly encouraged for signifi cant windows. 

Assigning an accurate date, maker, and style to a stained 

glass window oft en requires extensive research and 

professional help. A documentation and recording 

project, however, is worth the eff ort and expense, as 

insurance against accidents, vandalism, fi re and other 

disasters. The bett er the information available, the bett er 

the restoration can be. The following sources off er some 

guidelines for dating leaded windows.

Building Context. The history of the building can 

provide ready clues to the history of its leaded windows, 

doors, and other elements. The construction date, 

and dates of major additions and alterations, should 

be ascertained. Later building campaigns may have 

been a time for reglazing. This is especially the case 

with churches and temples. They were oft en built 

with openings glazed with simple or generic clear 

leaded glass. Stained glass was added later as fi nances 

allowed. Conversely, the windows may be earlier than 

the building. They may have been removed from one 

structure and installed in another (once again, this is 

more likely with religious structures). Bills, inventories, 

and other writt en documents oft en give clues to the 

date and composition of leaded glass. Religious 

congregations, fraternal lodges, historical societies and 

other preservation organizations may have writt en 

histories that can aid a researcher.

Inscriptions and Signatures. Many studios 

and artists affi xed signature plates to their 

work—oft en at the lower right hand corner. 

In the case of Tiff any windows, the signature 

evolved through several distinct phases, 

and helps date the piece within a few years: 

Tiff any Glass Company (1886-1892), Tiff any 

Glass & Decorating Company (with address, 

1892-1902), Tiff any Studios New York or Louis 

C. Tiff any (post 1902). (Tiff any Studios, like 

others, did not always sign pieces and the 

absence of an inscription cannot be used 

to rule out a particular studio or artist.) 

Windows may also feature dated plaques 

commemorating a donor. However, these do 

not always indicate the date of the window, 

since windows were oft en installed before a 

donor was found. Nevertheless, such marks 

help establish a reasonable date range.

Composition and Other Stylistic Elements. 

These elements are more subjective, and call 

for a fairly broad knowledge of architecture 

and art history. Do the windows fi t the 

general style of the building? The style of the 

window may refl ect a stylistic period (e.g., 

Arts & Craft s, Art Nouveau, Prairie School). 

The imagery or iconography of the windows may also 

reveal their overall historical context and establish a 

general time period. 

Framing and Surround. Framing elements and the 

window surround can reveal information central to 

dating the window. Do moldings match other interior 

trim? Has the opening been altered? Is the window set 

in an iron frame (post-1850s), a steel frame (generally 

post-World War I), a cast stone or terra cott a frame 

(seen as early as the 1880s, but popular aft er 1900)?

Reinforcement and Leading Details. Does the 

window or other element have round bars or fl at 

Figure 10. This 

lead-silhouett e 

stained glass face 

graces a 1928 coach 

house in Buff alo, 

and is att ributed to 

D’Ascenzo Studios of 

Philadelphia. 

Figure 9. A typical 

mail-order catalog page 

of art glass windows 

available in 1903 

from the E. L. Roberts 

Company, Chicago.
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bars? Flat bars began to appear about 1890; round 

bars, used since the Middle Ages, remained in use 

until the 1920s, when fl at bars supplanted them. 

Cames can also give dating clues. Zinc cames, 

for example, developed by Chicago Metallic 

in association with Frank Lloyd Wright, fi rst 

appeared in 1893. In general, however, dating a 

window by the came alone is diffi cult unless it is 

disassembled to view the “heart” (center web) for 

millmarks. Over one hundred varieties of lead 

came were available in the early 20th century. 

Moreover, came was sometimes produced to look 

old. Henderson’s Antique Leading from the 1920s 

was made “to resemble the old hand wrought 

lead” and also carried “easy-fi x” clip-on Georgianstyle ornaments.

Glass. The glass itself can help in dating a window. 

Opalescent glass, for instance, was patented 

by John LaFarge in 1879. Tiff any patented two 

variations on LaFarge’s technique in the same year. 

(Opalescent glass is translucent, with variegated 

colors resulting from internally refracted light. It 

features milky colored streaks.) Pre-1880 glass is 

usually smooth translucent colored glass (painted 

or not); glass with bold, deep colors is typical of the 

1880s and 1890s, along with jewels, drapery glass 

and rippled glass. But such fl amboyance faded out 

with the rest of Victoriana by about 1910. However, 

stained glass styles of the late 19th century 

continued to appear in ecclesiastical buildings aft er 

they passed from general fashion. Leaded beveled 

plate glass was popular in residential architecture 

aft er 1890, and was used profusely until the 1920s.

The level of documentation warranted depends 

upon the signifi cance of the window, but it is very 

important to document repair and restoration 

projects before, during, and aft er project work. 

Photographs will normally suffi ce for most 

windows. For highly signifi cant windows, rubbings 

as well as writt en documentation are recommended. 

The leading patt erns in such windows are complex, 

particularly in plated windows (which have several 

layers). Rubbings are therefore encouraged for each 

layer when restored; they are invaluable if a disaster 

occurs and reconstruction is required. Annotated 

rubbings of the leadwork should be done with a wax 

stone on acid-free vellum. 

To document windows properly, inscriptions should 

be recorded word for word, including misspellings, 

peculiarities in type style, and other details. Names 

and inscriptions in or on windows can indicate 

ethnic heritage, particularly in churches or civic 

structures where windows oft en refl ect styles and 

themes from the congregation or community’s 

origins. Lastly, any conjectural information should 

be clearly noted as such.

The Importance of Context

Stained glass commissioned for a particular building 

was normally designed not only to refl ect the shape 

of the opening but also to coordinate with other 

aspects of the overall sett ing such as the architectural 

style, adjacent materials, and interior decoration. The 

window opening, frame or sash colors, placement 

of the reinforcement, alignment with architectural 

elements, and orientation to natural light also establish 

the relationship between the stained glass and the 

building. The vibrant colors of opalescent glass, 

which can oft en be read from the exterior, and the 

linear designs of Prairie School windows, which oft en 

harmonize with both the interior and the exterior, are 

two examples that readily demonstrate the importance 

of architectural context to ornamental glass. 

This important relationship between the glass and its 

sett ing, however, can be weakened or entirely lost over 

the years due to unsympathetic decorating schemes 

or building campaigns, damage, deterioration, inept 

repairs, or the mere accumulation of dirt. 

Changes to the ornamentation and fi nish of the 

structural frame can have an especially pronounced 

eff ect on the overall appearance of a stained glass 

window or dome. In the Chicago Cultural Center 

dome the historic fi nishes of the ornamental cast iron 

frame have darkened 

considerably over 

the years, muting the 

dome’s rich personality. 

In strong sunlight the 

glass is so dominant 

that the frame appears 

only as a silhouett e. 

Restoring the vibrancy 

of the historic fi nish is 

necessary to recapture 

the equally important contribution of the frame to 

the original design intent of the dome. Aft er careful 

investigation to document the historic appearance 

(right), a mock-up section of the frame was regilded 

with aluminum leaf (top). The dramatic eff ect of 

restoring the dome’s overall context is readily apparent 

aft er only this small section of the frame was refi nished. 
7

Deterioration of Stained and Leaded Glass 

Three elements of leaded glass units are prone to 

damage and deterioration: the glass itself; the decorative 

elements (mostly applied paint); and the structural 

system supporting the glass.

Glass Deterioration

Glass is virtually immune to natural deterioration. 

Most American glass is quite stable—due to changes 

in glass composition made in the mid-19th century, 

particularly the increased silica content and the use of 

soda lime instead of potash as a source of alkali. Rarely, 

however, glass impurities or poor processing can cause 

problems, such as minor discoloration or tiny internal 

fractures (particularly in opalescent glass). And all glass 

can be darkened by dirt; this can oft en be removed. 

However, while glass does not normally deteriorate, 

it is susceptible to scratching or etching by abrasion or 

chemicals, and to breakage.

The greatest cause of breakage or fracture is physical 

impact. Leaded glass in doors, sidelights, and low 

windows is particularly susceptible to breakage from 

accidents or vandalism. When set in operable doors 

or windows, leaded glass can crack or weaken from 

excessive force, vibration, and eventually even from 

normal use. Cracks can also result from improperly 

set nails or points that hold the window in the frame, 

or more rarely, by structural movement within the 

building. Leaded glass that is improperly annealed 

can crack on its own from internal stress. (Annealing is 

the process by which the heated glass is slowly cooled; 

the process is akin to tempering metal.) Glass can also 

disintegrate from chemical instability or the intense heat 

of a fi re. Finally, windows assembled with long, narrow, 

angular pieces of glass are inherently prone to cracking. 

Oft en the cause of the cracks can be determined by the 

path they travel: cracks from impact typically radiate 

straight from the source. Stress cracks caused by heat 

or improper annealing will travel an irregular path and 

change direction sharply.

Deterioration of Painted Glass

Painted glass, typically associated with pictorial scenes 

and fi gures found in church windows, oft en presents 

serious preservation challenges. If fi red improperly, 

or if poor quality mixtures were used, painted glass is 

especially vulnerable to weathering and condensation. 

Some studios were notorious for poorly fi red paints 

(particularly those working with opalescent glass), 

while others had outstanding reputations for durable 

painted glass. Paints can be applied cold on the glass or 

fused in a kiln. Since they are produced from ground 

glass, enamels do not “fade,” as oft en suggested, but 

rather fl ake off in particles. Several steps in the painting 

process can produce fragile paint that is susceptible 

to fl aking. If applied too thick, the paint may not fuse 

properly to the glass, leaving small bubbles on the 

surface. This condition, sometimes called “frying,” 

can also result from poor paint mixtures or retouching. 

Paint failure is more commonly caused by under fi ring 

(i.e., baking the glass either at too low a temperature or 

for too litt le time). Unfortunately, in American stained 

glass, the enamels used to simulate fl esh tones were 

typically generated from several layers that were fi red 

at too low a temperature. This means the most diffi cult 

features to replicate—faces, hands and feet—are oft en 

the fi rst to fl ake away (Fig. 11).

Structural Deterioration

The greatest and the most common threat to leaded 

glass is deterioration of the skeletal structure that 

holds the glass. The structure consists of frame 

members, and lead or zinc (and occasionally brass or 

copper) came that secures individual pieces of glass. 

Frame members include wood sash and muntins that 

decay, steel t-bars and “saddle bars” that corrode, and 

terra cott a or stone tracery that can fracture and spall 

(Fig. 12). When frames fail, leaded glass sags and 

cracks due to insuffi cient bracing; it may even fall out 

from wind pressure or vibration. 

Wood sash are nearly always used for residential 

windows and are common in many institutional 

windows as well. Left unprotected, wood and glazing 

compounds decay over time from moisture and 

exposure to sunlight—with or without protective storm 

glazing—allowing glass to fall out. 

Figure 11. The face paint has failed substantially in the fi gure at the 

left . Ghost images of the feature are barely visible. Window (1903) 

by Edwin P. Sperry, glass by Tiff any Studios; “Old Main,” (1891-

1893) Illinois Institute of Technology, Chicago. Photo: Rolf Achilles.
8

Steel frames and saddle bars (braces) corrode when not 

maintained, which accelerates the deterioration of the 

glazing compound and loosens the glass. Moreover, 

operable steel ventilators and windows are designed to 

tight tolerances. Neglect can lead to problems. Eventually, 

they either fail to close snugly or corrode completely shut. 

The leaded glass is then frequently reinstalled in aluminum 

window units, which require wider sections for equal 

strength and typically results in an inch or more of the 

glass border being trimmed. Instead of relocating glass in 

aluminum frames, historic steel frames should be repaired. 

Oft en the corrosion is superfi cial; frames in this condition 

need prepping, painting with a good zinc-enriched paint, 

and realigning in the frame.

Masonry frames typically last a long time with few 

problems, but removing leaded glass panels set in 

hardened putt y or mortar can be nearly impossible; as 

a last resort, glass borders may have to be sacrifi ced to 

remove the window. 

Occasionally, leaded glass was designed or fabricated 

with inadequate bracing; this results in bulging or bowing 

panels; leaded panels should generally not exceed 14 linear 

feet (4.25 m) around the perimeter without support. More 

oft en, the placement of bracing is adequate, but the tie-wires 

that att ach the leaded panels to the primary frame may be 

broken or disconnected at the solder joints.

Lead and zinc cames are the two most common assembly 

materials used in stained and other “leaded” glass. The 

strength and durability of the leaded panel assembly 

depends upon the type of came, the quality of the 

craft smanship, and the glazing concept or design, as well 

as on the metallic composition of the cames, their crosssection strength, how well they are joined and soldered, 

and the leading patt ern within each panel. Came is prone 

to natural deterioration from weathering and from thermal 

expansion and contraction, which causes metal fatigue. 

The inherent strength of the assembly system is also related 

to the cross-section, profi le and internal construction of 

Came Types and Properties

Lead Came

Lead is a soft malleable metal (it can be 

scratched with a fi ngernail). It naturally 

produces a protective dark bluish-gray 

patina. In the mid-19th century, improved 

smelting processes enabled manufacturers to 

extract valuable metal impurities from lead, 

thereby producing 100% pure lead came. 

The industry reasoned that 100% pure lead 

came was superior to the less pure variety. 

Although pure lead came is very workable 

and contributes to intricate designs, time has 

proven it to be less durable than medieval 

came, which contained trace elements of tin, 

copper, silver, and antimony. Unfortunately, 

the misconception that pure lead had greater 

longevity continued throughout the glory 

years of leaded glass use in America. Most 

glass conservators use a 100-year rule of 

thumb for the general life expectancy of 19th 

century came. In the 1970s, “restoration 

lead” (ASTM B29-84) was developed based 

on metallurgic analyses of medieval cames, 

some of which have lasted for centuries. 

Restoration lead should always be used 

when releading historic windows, unless the 

original integrity will be compromised.

Zinc Came

Zinc came is more vulnerable to atmospheric 

corrosion (particularly from sulfuric acids) 

than lead, but has proven to be durable in 

America because it weighs 40% less than 

lead and its coeffi cient of expansion is 7% 

lower. Thus, it is somewhat less susceptible 

to fatigue from expansion and contraction. 

Moreover, it is ten times harder than lead, 

and has three times the tensile strength. Zinc 

came is strong enough to be self-supporting 

and requires litt le bracing to interrupt the 

window’s design. While zinc came is perfect 

for the geometric designs of Prairie School 

windows, it is usually too stiff to employ 

in curvilinear designs. Zinc can also take 

several fi nishes, including a copper or black 

fi nish. (As a result, zinc can be mistaken for 

copper or brass.)

Other Came

Other metals, primarily solid brass and 

copper, were also occasionally employed 

as came. They are generally found only in 

windows between ca. 1890 and ca. 1920. 

Frank Lloyd Wright started with zinc in 1893, 

was plating the zinc with copper by the late 

1890s, and using solid copper by 1906.

Figure 12. Stained glass frames are typically wood, steel or stone; 

however, other materials, and their inherent problems, can also be found 

as seen in this photograph of cracked terra cott a frames from 1926. 
9

the came (Fig. 13). Came can have a fl at, rounded, or 

“colonial” profi le, and aside from a few specialty and 

perimeter cames (U-channel), is based on a variation of 

the lett er “H” and ranges from 1/8” (3.2mm) wide to 11⁄2” 

(38mm) wide. The cross-section strength of came varies 

depending on the thickness of the heart and fl anges. 

Occasionally, came with reinforced (double) hearts or 

a steel core was used for rigidity, usually in doors and 

sidelights. Such came added strength at the expense of 

fl exibility and was typically used for rectilinear designs, 

or for strategically placed reinforcement within a 

curvilinear design. 

How the cames are joined in a leaded panel is crucial 

to their long-term performance. Poor craft smanship 

leads to a weak assembly and premature failure, while 

panels fabricated with interlocking (weaving) cames 

and lapped leads add strength. Soldered joints oft en 

reveal the skill level of the artisan who assembled the 

window, and can give evidence of past repairs. Solder 

joints should be neat and contact the heart of the came-

-wherein lies its greatest strength. Came joints should 

be examined closely; large globs of solder commonly 

conceal cames that do not meet. (Lead cames typically 

crack or break along the outside edge of the solder joint; 

stronger zinc cames frequently break the solder itself 

where it bridges junctures.) 

Leading patt erns designed with inadequate support 

also contribute to structural failure. Panels with a series 

of adjacent parallel lines tend to hinge or “accordion,” 

while lines radiating in concentric circles tend to 

telescope into a bulge. Stronger leading techniques, 

support bars, or specialty cames are sometimes required 

to correct poor original design. Minor sagging and 

bulging is to be expected in an old window and may 

not require immediate action. However, when bulges 

exceed 11⁄2” (38mm) out of plane, they cross into a 

precarious realm; at that point, glass pieces can crack 

from severe sagging and pressure. If the bulged area 

moves when pressed gently, or if surrounding glass is 

breaking, it is time to address the problem before serious 

failure results.

Cleaning, Repair and Protection 

The level of cleaning, repair, or protection depends on 

the condition, quality, and signifi cance of the glass, and, 

as always, the available budget. Hastily undertaken, 

overly aggressive, or poorly executed repairs can cause 

more damage than does prolonged deterioration. 

Repairs should, therefore, only be undertaken aft er 

carefully evaluating the condition of the glass—and 

only by professionals. Minor cracks, sagging, and 

oxidation are part of the character of historic leaded 

glass, and require no treatment. More extensive cracks, 

major bulges (generally, more than 11⁄2” [38mm]), and 

other signs of advancing deterioration may call for 

intervention, but caution must always be exercised. 

And each window must be evaluated separately. In 

some cases, windows have bulged up to 4” (102mm) 

out of plane without harming the pieces of glass or 

risking collapse.

Cleaning 

Perhaps the greatest virtue of stained glass is that its 

appearance is constantly transformed by the everchanging light. But dirt, soot, and grime can build up 

on both sides of the glass from pollution, smoke, and 

oxidation. In churches the traditional burning of incense 

or candles can eventually deposit carbon layers. These 

deposits can substantially reduce the transmitt ed light 

and make an originally bright window muted and 

lifeless. Simply cleaning glass will remove harmful 

deposits, and restore much of its original beauty, while 

providing the opportunity to inspect its condition 

closely (Fig. 14). The type of cleaner to use depends 

on the glass. Water alone should be tried fi rst (soft 

water is preferable); deionized water should be used 

for especially signifi cant glass and museum quality 

restorations. If water alone is insuffi cient, the next step 

is to use a non-ionic detergent. Occasionally, windows 

are covered with a yellowed layer of shellac, lacquer, 

varnish, or very stubborn grime that requires alcohol, 

or solvents to remove. Most unpainted art glass can 

be treated with acetone, ethanol, isopropyl alcohol, 

or mineral spirits to remove these coatings if gentler 

methods have failed. All chemical residues must then be 

removed with a non-ionic detergent, and the glass rinsed 

with water. (All workers should take normal protective 

measures when working with toxic chemicals.)

Figure 13. A wide variety of came has been used for ornamental glass 

in America: (a) fl at lead came; (b) round lead came; (c) “Colonial” 

zinc came; (d) double-heart lead came with a steel core; (e) “Prairie 

School” zinc came.

(c)

(a)

(e)

(b)

(d)

Flange

Heart
10

Painted glass must never be cleaned before the stability of 

the paint is confi rmed, and only then with great caution. 

If the paint is sound, it can be cleaned with soft sponges 

and cloth. If the paint was improperly fi red or simply 

applied cold, paint can fl ake off during cleaning and 

special measures are required such as delicate cleaning 

with cott on swabs. Occasionally, paint is so fragile the 

owner must simply document and accept the windows 

in their current state rather than risk losing the original 

surface. Fragile paint typically calls for an experienced 

glass conservator and more costly restoration measures.

Acidic, caustic, or abrasive cleaners should never be 

used. They can damage glass. Most common household 

glass cleaners contain ammonia and should not be used 

either. Cleaning products should have a neutral pH.

Repair

As with all elements in older and historic buildings, 

maintenance of leaded glass units is necessary to prevent 

more serious problems. It is essential to keep the frame 

maintained regardless of the material. Oft en, this simply 

entails regular painting and caulking, and periodic 

replacement of the glazing compound. Wood frames 

should be kept painted and caulked; new sections 

should be spliced into deteriorated ones, and epoxy 

repairs made where necessary. Masonry frames must be 

kept well pointed and caulked to prevent moisture from 

corroding the steel armature and anchors within.

Windows that leak water, are draughty, or ratt le in the 

wind (or when gently tapped) may indicate that the 

waterproofi ng cement (“waterproofi ng”) and sealants 

have deteriorated and maintenance or restoration is 

needed. Waterproofi ng is a compound rubbed over 

the window—preferably while fl at on a table—and 

pressed under the came fl ange to form a watertight 

bond between the leading and the glass. Traditionally, 

waterproofi ng was made of linseed oil and whiting, 

and a coloring agent. (Hardening agents should not be 

included in the mixture; solvent-based driers should 

be used sparingly.) The waterproofi ng allows leaded 

glass in a vertical position (e.g., in windows) to be used 

as a weatherproof barrier. It does not provided adequate 

protection for leaded glass in a horizontal or arched 

position; leaded glass ceilings and domes must always be 

protected by a secondary skylight or diff using skylight.

Glazing and sealants (e.g., putt ies, caulks) are used to seal 

the leaded panel against the sash, and to seal any open 

joints around the window frame. Sealants improved 

dramatically in the mid-twentieth century. But these 

sealants are not without problems. Some release acetic acid 

as they cure. Acetic acid can harm lead, and should never 

be used on leaded glass. Instead, “neutral cure” sealants 

should be used. These high-performance construction 

sealants are not sold in consumer supply stores. 

The appropriate type of sealant depends on the materials 

to be bonded and on the desired appearance and longevity. 

When windows are to be restored, the contractor should 

explain what types of waterproofi ng and sealants are to 

be used, and how long they are expected to last. On large 

projects, a lett er from the product manufacturer should 

be obtained that approves and warranties the proposed 

application of their product. When in doubt, a traditional 

linseed-oil based glazing putt y is oft en best.

Leaded panels will generally outlast several generations 

of waterproofi ng. When the waterproofi ng has failed, 

the window should be removed from the opening 

and waterproofed on a bench. Leaded glass cannot be 

adequately waterproofed in place. Removing the windows 

will provide an opportunity to perform maintenance on 

the window surround and to secure the reinforcement. 

This is far less expensive than totally releading the 

window, which is typically required if maintenance is 

deferred. When waterproofi ng or sealants break down, 

many building owners att empt to resolve the problem 

by installing protective glazing, when the window only 

needs maintenance. Protective glazing is not an alternative 

to maintenance; in fact, it impedes maintenance if not 

installed properly and can accelerate the deterioration of 

the stained glass.

A very common—but extremely harmful—practice in 

the American stained glass industry is performing major 

window repairs in place. The practice is routine among 

churches where the cost of restoring large windows can be 

prohibitive. However, undertaking major repairs in place 

provides only a quick fi x. A window cannot be properly 

repaired or restored in place if it is bulging or sagging far 

out of plane, if over 5% of the glass is broken, or if solder 

joints are failing. Unscrupulous glazers can introduce a 

great deal of stress into the glass by forcibly fl att ening the 

window in place and soldering on additional bracing. At a 

comfortable distance the window may look fi ne, but upon 

close inspection the stress cracks in the glass and broken 

solder joints become obvious. Windows subjected to this 

treatment will deteriorate rapidly, and complete, much 

more costly restoration will likely be necessary within 

a few years (while a proper repair can easily last two 

generations or more).

Figure 14. The external glass plate has been removed to clean the 

interlayer of this plated Tiff any Studios window. 
11

Major repairs to windows are sometimes 

part of a larger preservation project. In 

such cases, the risk of damaging the 

windows can be very great if their removal 

and reinstallation have not been carefully 

planned. When major building repairs 

are also to take place, the windows should 

be removed fi rst to prevent damage 

during other work. Windows should 

be reinstalled as the next-to-last step 

in the larger project (followed by the 

painters or others working on the fi nishes 

surrounding the stained glass).

And glass should be protected whenever 

other work is undertaken on buildings-

-whether or not the windows are also 

to be repaired. External scaff olding, for 

example, erected for repointing or roofi ng 

projects, may off er vandals and thieves 

easy access to windows and, through 

them, to building interiors. Stained 

and leaded glass should always be well 

protected whenever chemical cleaners 

are used on the exterior of the building; 

some products, such as hydrofl uoric-acid 

cleaners, will cause irreversible damage. 

Repairs to Glass

Minor repairs, such as replacing a few 

isolated pieces of broken glass, can be 

performed in place. This work, typically 

called a “drop-in,” “stop-in,” or “openlead” repair, entails cutt ing the came 

fl ange around the broken piece of glass at 

the solder joints, folding it back to repair 

or replace the old glass, and resoldering 

the joints. Repairing a zinc came window 

is not as easy. Zinc cames are too stiff to 

open up easily, so they must be cut open 

with a small hack saw and dismantled 

until the broken area is reached. The 

glass is then repaired or replaced and 

the window is reassembled. New cames 

can be patinated to harmonize with 

the originals--but only with diffi culty. 

Repatination should never be att empted 

in place, since it is impossible to clean off 

harmful residues trapped under the came.

Original glass should be retained 

whenever possible, even though it may be 

damaged. Replacement glass that exactly 

or closely matches the original piece can 

be very diffi cult to fi nd, and costly to 

make. An endless variety of glass colors 

and textures were produced, and given 

the delicate chemistry of glassmaking, 

even samples from the same run can 

be noticeably diff erent. The traditional 

Photographing Stained Glass

Historic stained glass windows, laylights 

and domes should be documented to 

help ensure the best-quality restoration 

in the event of vandalism, fi re or other 

loss. Photographic documentation 

is also important for insurance and 

investigation purposes when vandalism 

or theft is involved. Given the highly 

photogenic nature of stained glass, 

photographs can also serve as artwork 

for guidebooks or other interpretive or 

publicity purposes; quality photographs 

can be especially worthwhile in 

fundraising eff orts.

Photographing stained glass is both 

challenging and rewarding. Windows and domes lit by daylight can seem 

to be ever changing in visual appearance. They can appear dramatically 

diff erent in any given photograph depending not only on the photographic 

equipment and sett ings used, but also on the time of day, degree of cloud 

cover, the ambient interior light, and a multitude of other factors. Moreover, 

photographs may diff er depending on the aspect to be captured. Painted 

fl esh areas and highly translucent Prairie School windows oft en “burn out” 

if photographed in bright sunlight, while faceted jewels and very dense or 

plated opalescent glass oft en look best in direct sunlight.

Generally, exposures should be bracketed to capture the full range of the 

stained glass; the variation in images can permit diff erent images to serve 

diff erent purposes. Under most circumstances, interior lights should be 

turned off , and the stained glass should be photographed in both transmitt ed 

light (no fl ash) and refl ected light utilizing a fl ash. The fl ash should ideally 

be positioned away from the camera to provide a raking light and to avoid 

refl ected “hot spots.” Although photographing with a fl ash will neutralize 

the transmitt ed light and black out the glass, it reveals the location and 

condition of the lead cames, braces, tie-wires, and other structural elements.

A tripod should be employed for a sharp image whenever using long 

exposures and higher apertures. The subject should be shot as level as 

possible to minimize the distortion known as “parallax.” Occasionally, 

when shooting a group of windows, it is benefi cial to develop a cardboard, 

Ecuboard, Masonite or similar cutout material to mask the window being 

photographed. Adjacent windows or windows on the opposite side of the 

room may need to be shaded or blocked to avoid “front lighting” on the 

window from competing with the transmitt ed light. Windows should also 

be photographed from the outside if there is no protective glazing to interfere 

with the view. This is particularly important with opalescent glass, which 

oft en was intended to be read from the exterior as well as the interior.

Some glass projects warrant a visual representation of the stained glass 

window to be in place during restoration. Aft er establishing the existing 

window dimensions, a photograph of the stained glass window can be 

enlarged to full scale and copied on adhesive-backed transparent fi lm. In 

essence a decal, it can then be applied to acrylic or polycarbonate sheets 

and used as a temporary replacement to fi ll the opening (above). Such fi lm 

decals are sensitive to light and will not last indefi nitely. However, they are 

reasonably convincing from a distance and can last a year or longer while the 

actual window is being restored.
12

secrecy that shrouds the glassmaking trade to this 

very day, as well as environmental bans of historically 

popular ingredients such as lead and cobalt for deep 

blues and greens, further hinders accurate reproductions. 

Therefore, it is nearly always bett er to use an imperfect 

original piece of glass than to replace it (Fig. 15). If the 

paint is failing on a prominent feature of a window, a 

coverplate of thin, clear glass can be painted and placed 

over the original. (The coverplates must be att ached 

mechanically, rather than laminated, so that they can 

be removed later if necessary.) A reverse image of the 

fading feature should be painted on the backside of the 

coverplate in order to get the two painted images as close 

together as possible. With repetitive designs, stencils can 

be created to produce multiple duplicates. 

Sometimes replacement is the only option. Fortunately, 

custom glass houses still exist, including the company 

that originally supplied much of the glass for Tiff any 

commissions. Stained and leaded glass has also 

experienced a resurgence in popularity, and American 

glassmakers have revived many types of historic glass.

When missing, shatt ered, or poorly matched glass from 

later repairs must be replaced, the new pieces should be 

scribed on the edge (under the came) with the date to 

prevent any confusion with original glass in the future.

Glass cracks will enlarge over time as the contacting 

edges grind against each other, whenever the window is 

subject to vibration, thermal expansion and contraction, 

and other forces such as building movement. Therefore, 

it is important to repair cracks across important features 

as soon as they are detected and while a clean break 

remains. Years ago, cracks were typically repaired with 

a “Dutchman” or “false lead” by simply splicing in a 

cover lead fl ange over a crack. Although this conceals 

the crack, it creates an even larger visual intrusion and 

provides no bond to the glass. Today, there are three 

primary options for repairing broken glass: copper foil, 

epoxy edge-gluing (Fig. 16), and silicone edge-gluing. 

These techniques diff er in strength, reversibility, and 

visual eff ect, and the appropriate repair must be selected 

on a case-by-case basis by a restoration specialist.

Copper Foiling: Copper foil has the longest history 

and, unless the glass is unstable, is generally the best 

option when a piece of glass has only one or two cracks. 

Copper foil is a thin tape that is applied along each side 

of the break, trimmed to a minimal width on the faces, 

and soldered. A copper wire can be soldered on where 

additional strength is required. However, copper foil 

repairs should not be used on unstable glass, since heat 

is required that can cause further damage. Copper foil 

produces a strong repair, is totally reversible, and has a 

negligible aesthetic impact (a 1/16” [1.6mm] wide line). 

Epoxy Edge-Gluing: This technique produces a 

nearly invisible line and is oft en used on painted glass, 

particularly focal points of a window such as a face, or 

a portion of sky intended to be one continuous piece. 

Epoxy can even be tinted to match the glass. It is also 

used for infusing shatt ered glass or microscopic cracks 

caused by intense heat from a fi re. Epoxy produces 

a very strong repair, but will deteriorate in sunlight 

and requires secondary glazing to protect it from UV 

degradation. Epoxy is the least reversible of the three 

techniques, and usually the most expensive. 

Silicone Edge-Gluing: This repair method has the 

lowest strength and should be used when a fl exible joint 

is desirable—if, for instance, the window will be under 

continuous stress. Silicone repairs are easily reversible, 

and can be removed with a razor blade—when they 

are done correctly, that is. Silicone edge-gluing is not 

the same as smearing silicone all over the glass. This 

unfortunate practice, seen throughout the country, is 

useless as a repair technique, and usually causes more 

damage than if the glass were left alone. Silicone is 

almost clear, but it refracts light diff erently from glass 

and is, thus, easily detectable. Silicone is not aff ected by 

temperature, humidity or UV light. Silicone repairs are 

typically the least expensive repair option.

Figure 15. To permit repair of the cracked glass, the original lead 

overlay is fi rst salvaged from this historic leaded panel of silhouett e 

glass to retain as much of the original work as possible. 

Figure 16. A valuable historic piece of original hand-painted glass is 

carefully edge-glued with epoxy. 
13

Repairs to Structural Support Systems

Windows may have detached from the saddle bars and 

begun to sag, bulge, and bow extensively. This point 

varies from window to window. Generally, however, a 

window sagging or bulging more than 11⁄2” (38mm) out of 

plane has reached the point where it should be removed 

from the opening to be fl att ened out. Under these 

conditions, it is essential to note if the support system or 

leading patt ern has failed so it may be corrected before 

the window is reinstalled. The window must be allowed 

to fl att en over a few weeks in a horizontal position. This 

will minimize stress on the solder joints and glass. A 

moderate weight and controlled heat will help coax the 

window back into its original plane. The process requires 

patience. Once the window has fl att ened, the original 

support system should be reatt ached and additional 

support added as necessary. It is crucial to consider the 

original design so the new support bars do not intrude on 

important window features. Sometimes small thin braces 

or “fi ns” can be manipulated to follow existing lead lines 

exactly. These give support, but are almost invisible. 

Flatt ening windows also provides a good opportunity 

to apply new waterproofi ng to help prevent further 

deterioration. Today, a wide variety of traditional and 

synthetic compounds are employed.

Windows should only be removed when they need to be 

fl att ened, waterproofed, reinforced, or releaded. Allow 

plenty of time for careful, thorough work. Large projects 

can take several months, especially if complete releading 

is necessary. Owners, consulting professionals, and 

construction managers must therefore ensure that vacant 

openings will be weathertight for an extended period—

whether the openings are covered by plywood, acrylics, 

or polymer fi lm. If desired, images of the window can be 

printed on adhesive fi lm and applied to rigid plastic and 

installed in the openings as temporary facsimiles during 

studio restoration. 

Rebuilding or releading a window is an expensive and 

involved process. The releading process requires that a 

window be disassembled before it can be reassembled 

(Fig. 17). The glass pieces must be removed from the 

cames, the old cement must be cleaned from each piece 

of glass, and all the pieces must be rejoined precisely. 

At every step the process involves the risk of damaging 

the glass. Furthermore, exceptional studios had unique 

leading techniques, and thus the cames should not 

be replaced casually. Total releading should only be 

undertaken when necessary to avoid or slow the loss 

of historic fabric. (It is essential to request a copy of all 

window rubbings if the windows are to be completely 

releaded.) 

Lead and zinc cames, however, are intended to be a 

sacrifi cial element of a glass unit assembly, as mortar 

is to brick and paint is to wood; came will break down 

long before glass and must ultimately be replaced; came 

typically lasts 75 to 200 years depending on the window’s 

quality, design and environment. A common preservation 

confl ict arises in releading historic windows: whether to 

retain historical accuracy by using the existing profi le, or 

to use came with a stronger profi le for greater longevity. 

The decision must be carefully weighed depending on 

the signifi cance of the window, the contribution of the 

came profi le to the overall design, and the severity of 

the deterioration caused by a thin or weak came. In 

most windows, the came profi le is essentially lost in 

transmitt ed light, but occasionally shadow lines are 

important and should be reproduced. Furthermore, 

it is important to correct technical problems that arise 

from fl imsy original came. Occasionally, a slightly 

heft ier came may be the best solution to resolve weak 

panels that have not proven the test of time. Under 

these circumstances, the thicker lead came (even if only 

1/64” [0.4mm]) will cause a re-leaded panel to swell 

slightly, and the frame or perimeter leads may have 

to be trimmed to fi t the opening. (Trimming the glass 

should be the very last resort.) This would not be an 

appropriate solution in a museum-quality restoration or 

for a highly signifi cant window.

Protective Glazing and Screens

The use of protective glazing (also known as 

secondary or storm glazing) is controversial. Potential 

benefi ts of protective glazing are that it can shield 

windows from wind pressure; increase energy 

savings; protect against environmental pollutants and 

UV light; provide vandalism and security protection, 

and reduce window maintenance. Potential 

drawbacks are that it can promote condensation; cause 

heat to build up in the air space and thereby increase 

the window’s expansion/contraction; eliminate natural 

ventilation; reduce access for maintenance; off er a 

poor energy payback for the cost, and signifi cantly 

mar the building’s appearance. Protective glazing is 

oft en presented as a cheaper alternative to full-scale 

restoration. And all too oft en protective glazing is 

installed as a routine matt er when there is litt le threat 

of damage from vandalism or other causes. Protective 

glazing, especially when improperly installed, may 

hasten deterioration of stained glass windows. 

Figure 17. Total releading is very time consuming and costly and 

should only be undertaken when the original lead is exhausted 

beyond repair.
14

Domes and Ceilings 

Stained glass domes and ceilings were very 

popular throughout the Victorian and Classical 

Revival periods. They are oft en principal 

interior features of churches, hotels, restaurants, 

railway stations, and civic buildings. The loss or 

unsympathetic alteration of leaded glass ceilings 

and domes is a widespread problem. Poorly 

planned rehabilitation projects sometimes cause 

the unnecessary removal or alteration of overhead 

leaded glass in order to comply with fi re codes or 

to achieve perceived energy savings; occasionally, 

they are even concealed above suspended ceilings.

Moreover, stained glass in the horizontal position 

readily collects dust and dirt over the years 

and is relatively inaccessible for cleaning. It is 

also more likely to “creep” or slump when the 

reinforcement is inadequate. Most importantly, 

leaded glass cannot be suffi ciently weatherproofed 

in a horizontal (or arched) position. It must always

be protected by skylights or “diff users”—rooft op 

features that diff use the natural daylight into the 

att ic or light shaft , and protect the leaded glass 

ceiling or dome from the elements (a).

Due to the inferior quality of glazing sealants of the 

late 19th and early 20th centuries, and to deferred 

maintenance, glass ceilings have frequently been 

removed or covered with roofi ng materials. 

Artifi cial lighting is then required to backlight the 

ceiling or dome, which robs the stained glass of its 

life−the vibrant eff ects created by ever-changing 

natural light. All types of artifi cial lighting can 

be found from fl oodlamps to fl uorescent tubes. 

Outside sensors are even used to modulate the 

light level in an att empt to simulate changes in 

daylight. However, daylight is impossible to 

emulate. Moreover, it’s free. Artifi cial lighting 

requires maintenance, introduces an additional 

fi re hazard in the att ic, increases the building’s 

electrical load, and is supplied only at a fi nancial 

and environmental cost.

Stained glass ceilings and domes that have been 

sealed off from natural light should be investigated 

for restoration. Once natural light is restored and 

the stained glass is cleaned, the lighting eff ect 

on an interior can be extraordinary. Improved 

skylight designs and major advances in glazing 

sealants since World War II (particularly silicones) 

encourage the restoration of skylights without the 

fear of inheriting a maintenance nightmare (b).

(a) Stained glass ceilings and domes are oft en principal interior 

features of churches, hotels, restaurants, railway stations, and 

civic buildings. This vaulted ceiling illuminates the Cypress Lawn 

Memorial Gardens mausoleum in Colma, California. The panel 

removed reveals the diff using skylight above.

(b) Workers install a jeweled art glass oculus of a Healy & Millet 

dome. The diff using skylight was restored overhead to reintroduce 

daylight to the historic 1897 dome aft er being roofed over since the 

1940s. 
15

Figure 18. On this pair of neo-gothic church windows, the 

aluminum frame grid used for protective glazing disregards 

the original tracery of the window on the left . The grid mars 

the appearance of the window inside and out. It also impairs 

the overall historic character of the building. The plastic 

storm glazing has been removed from the adjacent window to 

restore the original window appearance. 

Various types of metal grills or screens are also used. 

They add security and vandalism protection but also 

impair the appearance of the window (inside and out) 

by creating new shadows that telegraph on the stained 

glass or diff using transmitt ed light. As a general rule, 

protective layers should not be added on historic 

buildings unless the glass sett ing was designed for 

storm glazing. In most cases the potential drawbacks 

outweigh the potential benefi ts.

Under some circumstances, however, protective glazing 

or screens may be necessary. (This applies to windows. 

Domes and ceilings present a special case. See “Domes 

and Ceilings”). A real vandalism or security threat 

warrants protective glazing, such as when the windows 

can be reached easily or are in an isolated location. 

Protective glazing is also warranted when employed 

historically on a particular window as original plating 

(Tiff any Studios, for example, oft en used plate glass 

to keep dirt and moisture out of their multi-plated 

windows). Unusual circumstances (such as when the 

windows are painted on the outside) may also dictate 

the use of protective glazing. Finally, protective glazing 

is warranted when a UV fi lter is needed to prevent 

epoxy glass repairs from breaking down. 

A variety of protective glazing materials are available. 

They include polycarbonates, acrylics, laminated 

glass, plate glass, and tempered glass. The plastic 

products are very strong, lightweight, and relatively 

easy to install, but will scratch, haze, and yellow over 

time, despite UV inhibitors. They also have a high 

coeffi cient of expansion and contraction, so the frames 

must be designed to accommodate change induced 

by temperature fl uctuations. Poor installations in 

restrictive frames cause distorted refl ections from 

bowing panels oft en damaging the historic frame. 

Protective panels of glass are heavier and more diffi cult 

to install, making them more expensive than plastic. 

However, glass will not bow, scratch, or haze and is 

usually the best option in aesthetic terms; laminated 

glass provides additional impact resistance.

A common error in installing protective glazing is to 

create a new window confi guration (Fig. 18). Insensitive 

installations that disregard the original tracery destroy the 

window’s aesthetics—and the building’s. When protective 

glazing is added, it should be ventilated. If a window is 

not ventilated, heat and condensation may build up in the 

air space between the ornamental glass and the protective 

glazing (creating a “greenhouse eff ect”). 

When absolutely necessary, protective glazing should be 

installed in an independent frame between 5⁄8” (16mm) 

and 1” (25mm) from the leaded glass. This allows the 

protective panel to be removed for periodic maintenance 

of both the historic window and the new glazing. The 

conditions of the air space between the two layers should 

be monitored on a regular basis; condensation should 

never collect on the window. 

No ideal formulas have been developed for venting the 

air space between the ornamental glass and the protective 

glazing, but it is typically vented to the outside (unless the 

building is air conditioned most of the year). Generally, 

a gap of several inches is left at the top and bott om when 

glass is used, or holes are drilled in the protective glazing 

at the top and bott om when polycarbonates and acrylics 

are used. Small screens or vents should be added to keep 

out insects. Finally, it is important to realize that most 

original plating was “rough plate” or “ribbed” and never 

had a modern polished refl ection. Some glass tinted the 

transmitt ed light intentionally, as originally designed: in 

this case any new or replacement plating should simulate 

this eff ect to respect the artisan’s intention.

Conclusion

Much of the Nation’s stained glass and leaded glass has 

recently passed, or is quickly approaching, its 100th 

anniversary—yet much of this glass has not been cleaned 

or repaired since the day it was installed. With proper 

care, the stained and leaded windows, transoms, and other 

elements that add so much to historic buildings can easily 

last another century.
16

Wooden frame of the rose window undergoing repair (exterior view). 

Cover Photograph: Tiff any Studios opalescent art glass frame 

from 1914, originally installed in a dome over the Men’s Grill in 

Marshall Field’s, Chicago.

Acknowledgements

Neal A. Vogel is the Principal of Restoric, LLC, Evanston, Illinois. Rolf Achilles is an Art Historian and Curator of the Smith Museum of 

Stained Glass Windows at Navy Pier, Chicago. All drawings and photographs by Neal A. Vogel unless otherwise stated.

Michael J. Auer, Technical Preservation Services, National Park Service, served as technical editor. Additional assistance was provided 

by Charles Fisher, Anne Grimmer, and former staff Chad Randl, Technical Preservation Services. 

The authors would like to thank the following for sharing information and providing opportunities to review works in progress: Bott i 

Studios of Architectural Arts, Evanston, IL; Chicago Metallic Corporation, Chicago, IL; Chicago Art Glass and Jewels, Inc., Cedar 

Grove, WI; Conrad Schmitt Studios, Inc., New Berlin, WI; Cypress Lawn Memorial Park, Colma, CA; Hollander Glass, Stanton, CA; 

Mary Clerkin Higgins, New York, NY; Venturella Studios, New York, NY; Wardell Art Glass, Aurora, IL. Special thanks for providing 

editorial assistance to Arthur J. Femenella, Femenella & Associates, Branchburg, NJ; Richard L. Hoover, Stained Glass Association of 

America, Lee’s Summit, MO; and H. Weber Wilson, Oltz-Wilson Antiques, Portsmouth, RI.

This publication has been prepared pursuant to the National Preservation Act of 1966, as amended, which directs the Secretary of 

the Interior to develop and make available information concerning historic properties. Comments about this publication should be 

addressed to: Charles Fisher, Technical Publications Program Manager, Technical Preservation Services—2255, National Park Service, 

1849 C Street, NW, Washington, D.C. 20240. This publication is not copyrighted and can be reproduced without penalty. Normal 

procedures for credit to the authors and the National Park Service should be provided. The photographs used in this publication 

may not be used to illustrate other publications without permission of the owners. For more information about the programs of the 

National Park Service’s Technical Preservation Services, see our website at www.nps.gov/history/hps/tps.

ISSN: 978-0-16-078947-2

U.S. Government Printing Offi ce Stock Number: 024-005-01254-1 October 2007

Selected Reading List

Duthie, Arthur Louis. Decorative Glass Processes: Cutt ing, 

Etching, Staining, and Other Traditional Techniques. New York: 

The Corning Museum of Glass and Dover Publications, 1982.

Fisher, Charles E., III, ed. The Window Handbook: Successful 

Strategies for Rehabilitating Windows in Historic Buildings. 

Washington, D.C.: National Park Service and Georgia Institute 

of Technology. 1986. Rev. 1990.

Fisher, Charles E., III, Deborah Slaton, and Rebecca 

A. Shiff er, eds. Window Rehabilitation Guide for Historic 

Buildings. Washington, D.C.: Historic Preservation Education 

Foundation/National Park Service, 1997. 

Heinz, Thomas A. Lloyd Wright Glass Art. Academy Editions, 

Ernst & Sohn, 1994.

Heinz, Thomas A. “Use & Repair of Zinc Cames in ArtGlass Windows.” Old House Journal, (September/October 

1989), pp. 35-38.

Lee, Lawrence, George Seddon and Francis Stephans. Stained 

Glass. New York: Crown Publishers, 1976.

Lloyd, John Gilbert. Stained Glass in America. Jenkintown, PA: 

Foundation Books, 1963.

Stained Glass Association of America. SGAA Reference & 

Technical Manual, Second Edition Lee’s Summit, MO: The 

Stained Glass Association of America, 1992.

Wilson, H. Weber. Great Glass in American Architecture: 

Decorative Windows and Doors Before 1920. New York: E. P. 

Dutt on, 1986.