The recipes for glazed terracotta were closely guarded workshop secrets developed over decades and used by the Della Robbia family for about a century. The first step in the process was gathering earthen clay from riverbeds. Luca set a standard by seeking out the finest quality of clay available, a light-colored, chalky variety that bound particularly well with his lead-tin glazes. He then refined the clay through cleaning, sifting, and the addition of soft river sand.

The prepared clay was mixed with water and formed by hand-modeling, pressing it into molds, or a combination of the two techniques. A mold was used to replicate this composition. The two reliefs probably emerged from the same mold but were finished slightly differently, with details refined by hand and variations in glaze colors and applied gilding. The transparency and matte surfaces of the glaze, along with the “runny” quality of the glaze in the eyes of the New York version, suggest early experimentation with the new technique.

Larger sculptures in the round were made in pieces, often hollowed out, and joined together at a later stage. Production in sections facilitated the works’ transport to destinations outside Florence. This figure group for a church in Pistoia was built in four separate parts. Once the individual pieces were formed and the clay was air dried, they were fired in a kiln at approximately 1700 degrees Fahrenheit. This step was known as “bisque firing.” The process could take several days.

After bisque firing, the sculpture was coated with glazes, composed of finely ground glass, metallic compounds as colorants, and water. Della Robbia glazes contained a high proportion of tin and lead, which lent them an opaque, bright effect. The glazes were applied by brush, sometimes in a large field of a single color, sometimes in layers to achieve various tones and shades. Then the ceramic was fired a second time at a temperature of about 1650 degrees Fahrenheit to “vitrify” the glazes, or harden and fuse them with the clay below.

The glazes took on their colors by the addition of various metallic compounds: tin oxide for white, cobalt for bright blue, copper for green, manganese for purple, and lead and antimony for yellow. The only primary color that could not be achieved with glaze was red. Most Della Robbia sculptures were glazed in a limited palette of one to five hues. Luca’s great-nephew Giovanni, however, distinguished himself by the use of a wider range of color and detail. The expressive quality of his lunette relief of the Resurrection was intensified by glazes in a variety of realistic flesh tones and by the addition of paint and gilding after firing. This monumental work was first recorded in an outdoor setting, at the top of a portal in the garden of an Antinori villa outside Florence. The patron, shown in prayer, was a member of that Florentine patrician family. Recent conservation of the relief was supported by his descendants through Marchesi Antinori S.p.A.

In Giovanni’s Pietà, the skin tones of Mary and the dead Christ are not glazed. Instead, the terracotta is left in its natural color, enhanced by paint, to suggest the color of flesh without the addition of luminous white. Giovanni’s father, Andrea, seems to have introduced this treatment, which heightened realism, in Della Robbia holy figures of the 1490s. The innovation may have been in part a response to calls for greater simplicity and austerity in religious practice during the later 15th century.

The cathedral of Santa Maria del Fiore is the quintessential monument of Renaissance Florence, its towering masonry dome faced with terracotta tiles rhyming with the warm brick and stone of the city and complementing the green and blue tones of the surrounding hills.

Luca della Robbia completed several works of sculpture inside the cathedral, including one of the cantorie, or organ lofts, commissioned in the 1430s, when the dome was just being completed under the supervision of architect Filippo Brunelleschi.  The cantoria design features children singing, dancing, and playing instruments in praise of the Lord. This work demonstrates Luca’s skill as a sculptor in marble, another medium in which the Della Robbia excelled.

Luca also sculpted a pair of large-scale glazed terracotta reliefs for the lunettes above the sacristy doors in the cathedral, positions of special prominence to the left and right of the high altar.

The first relief represents Christ’s resurrection on the third day after his death on the cross. Luca’s figures stand out strongly against the blue background by virtue of their modeling and white color, rendering them clear and readable even at a distance. The companion relief depicts the ascension of Christ to heaven 40 days after his resurrection. This composition is distinguished by a greater variety of color, especially in the greens that characterize the earthly realm from which Jesus ascends.

Originally a grain market, the large building known as Orsanmichele later became a church supported by Florence’s professional trade guilds. Luca della Robbia created glazed terracotta roundels depicting the coats of arms of three such guilds; the sculptures are placed high above the tripartite arcades. Renaissance Florentines would have encountered them while walking on the main street leading from the civic center of Piazza della Signoria to the cathedral.

Luca’s roundel honoring the association of doctors, pharmacists, and spice merchants presents the guild’s protectors, the Madonna and Child, against a patterned background of green, yellow, and blue that may represent a luxurious fabric. Lilies, symbolic of both the Virgin and Florence, grow alongside the arched shrine that surrounds the figures.

The bright, durable colors of Della Robbia glazes were particularly suitable for making coats of arms—of guilds, religious institutions and orders, and families—which were often set into the exterior walls of buildings or courtyards. A coat of arms of the Franciscan order, attributed to Luca’s great-nephew Luca della Robbia the Younger, appears in the exhibition. So does a Madonna and Child statuette by Luca himself, glazed with a range of colors similar to his Madonna in the coat of arms for the guild of doctors and pharmacists at Orsanmichele.

The Ospedale degli Innocenti (Hospital of the Innocents), dedicated to the care of orphaned and abandoned children, was designed by Filippo Brunelleschi in the 15th century with an elegant loggia, or covered arcade, overlooking Piazza Santissima Annunziata. Andrea della Robbia decorated the spandrels of the loggia with circular reliefs of swaddled infants on a blue ground.

The Innocenti roundels count among the most recognizable productions of the Florentine Renaissance. The figures are represented as individuals deserving of charity. Each baby appears different in pose, swaddled in various colors, each face unique in character and expression. Collectively, the reliefs manifest a new Renaissance interest in childhood as a distinct stage of life. The Della Robbia showed a particular affinity for the representation of children, their sculptures both reflecting and serving to shape perceptions of youth in 15th-century Florence.

Affecting images of children from the family’s workshop feature prominently in the exhibition. Like the Innocenti foundlings, this pair of reliefs by Andrea was once part of a series integrated into an architectural setting. Sensitive modeling and variations in pose evoke each subject’s unique character.

Between about 1440 and 1461, the Della Robbia adorned another of Brunelleschi's works: the chapter house in the cloister of the Franciscan church of Santa Croce. Named the Pazzi chapel for its patron, the building, with its elegant portico and cupola, became an influential example of modern architecture founded on classical principles.

Luca sculpted circular medallions of the 12 Apostles, the early disciples of Jesus and preachers of the Gospel, including Andrew, James, and John, for the walls of the chapel interior. The roundels are glazed primarily in the signature Della Robbia colors of white against blue.

Luca also complemented the architect’s design for the cupola of the portico by covering its inner surface with a coffered pattern of molded tiles. At center appears the Pazzi coat of arms encircled by a fruit and flower garland. Around this, circles of blue and yellow rosettes, ringed with green, leafy wreaths, gradually expand in scale. This brilliantly colorful, reflective, and long-lasting decoration created an effect of opulence contained by rigorous geometry. Both the cupola and its decoration were completed well after Brunelleschi’s death in 1446.

These portrait reliefs in the exhibition are set within roundels encircled by garlands of fruit and leaves, similar to the wreath at the center of the Pazzi cupola ceiling. The individualized expressions of the figures, a young man and an elderly saint, show similarities to the apostles of the chapel walls.

In the last decade of the 15th century, Giovanni della Robbia worked in the sacristy of the great Dominican church of Santa Maria Novella. The magnificent façade of patterned green and white stone was designed by the architect Leon Battista Alberti.

Here Giovanni created a lavabo, or washbasin, whose elaborate design comprises carved marble, painted flat tiles, pilasters decorated with figural sculpture, and an early example of pure landscape imagery in the glazed terracotta lunette. Children standing on the cornice support heavy swags of fruit and leaves on their shoulders. Before this cornucopia of sculptural elements suggesting themes of purification and natural abundance, the priest would wash his hands and cleanse his spirit before moving to the altar.

Other Della Robbia sculptures incorporating the forms of Renaissance architecture to serve the needs of churches include this tabernacle featured in the exhibition. In the glazed relief, angels venerate the bread for the sacrament of communion, once contained in a rectangular receptacle under a vault hung with curtains at the center.