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Japanese porcelain Hirado ware paperweight with chrysanthemums and plum blossoms, underglaze blue and brown, 19th-century
Dish with cypress, Turkey, Iznik, c. 1575, underglaze-painted stonepaste – Royal Ontario Museum – DSC04735

Underglaze is a method of decorating pottery in which painted decoration is applied to the surface before it is covered with a transparent ceramic glaze and fired in a kiln. Because the glaze subsequently covers it, such decoration is completely durable, and it also allows the production of pottery with a surface that has a uniform sheen. Underglaze decoration uses pigments derived from oxides which fuse with the glaze when the piece is fired in a kiln. It is also a cheaper method, as only a single firing is needed, whereas overglaze decoration requires a second firing at a lower temperature.[1]

Many historical styles, for example Persian mina'i ware, Japanese Imari ware, Chinese doucai and wucai, combine the two types of decoration. In such cases the first firing for the body, underglaze decoration and glaze is followed by the second firing after the overglaze enamels have been applied. However, because the main or glost firing is at a higher temperature than used in overglaze decoration, the range of colours available in underglaze is more limited, and was especially so for porcelain in historical times, as the firing temperature required for the porcelain body is especially high. Early porcelain was largely restricted to underglaze blue, and a range of browns and reds. Other colours turned black in a high-temperature firing.[2]

Examples of oxides that do not lose their colour during a glost firing are the cobalt blue made famous by Chinese Ming dynasty blue and white porcelain and the cobalt and turquoise blues, pale purple, sage green, and bole red characteristic of İznik pottery – only some European centres knew how to achieve a good red.[3] The painting styles used are covered at (among other articles): china painting, blue and white pottery, tin-glazed pottery, maiolica, Egyptian faience, Delftware. In modern times a wider range of underglaze colours are available.

An archaeological excavation at the Tongguan kiln Site proved that the technology of underglaze colour arose in the Tang and Five Dynasties periods and originated from Tonguan, Changsha.[4] However cobalt blue was first used in Persian pottery.[5] The technique has been very widely used for earthenware and porcelain, but much less often on stoneware.[6]

History

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Ptolemaic faience

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Ancient Egyptian faience production in the New Kingdom period employed the use of underglaze in works producing green and blue pieces that are distinct from other eras of production. This was achieved by the use of an underglaze that contrasts with the overglaze.[7] This produces the effect of highlighting and lending spectral variance to relief patterns that are embossed into pieces such as tableware such as bowls or jars. Desired blue and green finishes were achieved with the use of copper oxide on their glazing process. Ptolemaic faience has a self-glazing process. In addition to not using successive layers of glaze after the underglaze, Ptolemaic faience also applied a lower kiln temperature.[8][9] At the firing stage a bake between 900 and 1,000 °C (1,650 and 1,830 °F) is applied to achieve a spectrum between turquoise blue and green. Underglaze in Ptolemaic faience was widely used for Ushabti dolls en masse for grave goods in the late Kingdom period.

Chinese porcelain

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Chinese porcelain dish with the typical Ming underglaze blue on white porcelain, Xuande Reign 1426–1435, Ming

Through the Yuan and Ming dynasty, Imperial porcelain was produced with red oxide under glazes and more popular cobalt blue.[10] Cobalt blue underglaze porcelain was adopted into the imperial style for both domestic production and Chinese export porcelain under the Yuan, Ming and Qing dynasties. Until late in the Xuande period the cobalt was imported from Persia; it has specks with high iron and low manganese content.[11] This cobalt had a tendency to run when used in a tin glaze, and Persian artisans relied on the experimentation of the Chinese in Jingdezhen porcelain to achieve clear blue designs in their ceramics. Chinese whiteware was prized as an import to Islamic countries[12] that would then trade cobalt for the manufacture of more Chinese porcelain. This was changed to a Chinese form of cobalt that in its ore form had a higher composition of MnFe
2O
4 (Jacobsite) rather than Fe
3O
4 (Iron(II,III) oxide). Due to the Middle Eastern demand for blue and white porcelain the primary use of this underglaze technology was utilised in creating many designs with Islamic decoration.

Faience

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Most styles in this group, such as Delftware, mostly used blue and white pottery decoration.

Islamic world

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Classical İznik pottery from the Ottoman Empire has a stonepaste or frit body, and uses lead glazing rather than tin, and has usually been painted in polychrome.[13] Persian pottery, which was aware of Chinese styles throughout the period, made great use of underglaze decoration, but mostly in a single colour, often blue using the local cobalt, but also black.[14]

English transfer printed earthenware

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Transfer printed plate using two transfers, puce and green, c. 1830, Staffordshire pottery, Enoch Wood & Co.

Underglaze normally uses a transparent glaze, and therefore reveals the undecorated parts of the fired body. In porcelain these are white, but many of the imitative types, such as Delftware, have brownish earthenware bodies, which are given a white tin-glaze and either inglaze or overglaze decoration. With the English invention of creamware and other white-bodied earthenwares in the 18th century, underglaze decoration became widely used on earthenware as well as porcelain.

Transfer printing of underglaze was developed in England in Staffordshire pottery from the 1760s. The patterns were produced in the same way as printed engravings which were in industrial production at the time. A copper printing plate engraved with the design would transfer underglaze pigment to a piece of dampened tissue paper through a rolled press which could then be adhered to earthenware. The colourants were metallic pigments such as cobalt blue but also include the use of chromium to create greens and browns.[8] To ensure clean transfer, quick firing at a low temperature might be given to fix the colours, known as "hardening on".[15]

Initially most production just included one colour, but later techniques were developed for printing in several colours.[16] One type of English Creamware using blue, green, orange and yellow colours is known as "Prattware", after the leading manufacturer.[17] This technique was also used in Europe and America in the 19th century on Creamware.[18]

Current use

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Underglaze is available in a variety of colours from commercial retailers and is used in industrial production of pottery.[19] Low firing temperature underglazes have been formulated as well as application options such as in the form of liquid pens of glaze or solid chalk blocks. The application of underglaze techniques such as stained slips have diversified and a variety of artists have created independent chemical processes of their own to achieve desired effects. Within commercial production there is a decline in underglaze use in comparison to 18th century use due to the creation and improvement of other glazing techniques that do not require such a high heat point. The vibrancy that only underglaze was able to supply is now achievable with a variety of over-glazes therefore discounting the advantage that underglaze commercial production had.

A well-known New York underglaze tile and pottery decorator of the 1940s, Carol Janeway (1913-1989), was diagnosed with lead poisoning after eight years of using a lead-based overglaze, retiring in 1950. Her tiles' glazes tested strongly for lead in 2010 using X-Ray Fluorescence technology. [20]


Underglaze transfers

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Underglaze transfers are a technique that involves screenprinting or free handing a pattern onto a transfer paper (often washi paper or newspaper) which is then placed, dampened, and burnished onto the surface of a leather-hard piece of clay (similar to how a lick-and-stick tattoo might be applied).[21] Artists can acquire rice paper to make their own custom designs, and also purchase pre-printed designs online. Unlike overglaze decals, underglaze decals are often applied to greenware and bisque and fired at higher temperatures compared to their overglaze counterparts.

Forgeries

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The desirability of specific periods of white and blue underglaze Chinese porcelain has led to wide and sophisticated forgery operations. The collector market of blue and white underglaze porcelain is notable due to Orientalism's popularity in Europe. Counterfeiting operations have developed both in foreign areas and within China[22] to profit from the collectability of Ming and Qing dynasty blue and white porcelain. From the baroque period onward, there was a slight decline in the profitability of forging Chinese porcelain as European hard paste techniques were developed but kept as industry secrets in countries such as Germany and France. Despite this there still was and continues to be a high European demand for Chinese blue and White porcelain. In the last three decades there has been a considerable increase in demand for antiques of Ming and Qing porcelain amongst China's rising middle class, which has led to another growth in counterfeiting efforts to supply the large amount of new collectors. This counterfeiting is performed within China and sold to its own population unlike previous rushes in Europe.[citation needed]

Analysis of composition

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Due to the extensive efforts to counterfeit Chinese blue and white porcelain, there has been a promotion of detailed scientific analysis of the composition of cobalt used in the underglazes through xeroradiography which has provided insight to the chemical make up of original underglaze recipes on a chemical scale. This in turn reveals historical data about the supply and manufacture industry within China at the time of production of each piece.

Identification of pigment in scientific research

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Multiple enquires are being made in an academic and scientific context as to quantifying the physical and chemical composition of multiple types of underglaze. X-ray fluorescence is a primary building block if this but is not acceptable for full understanding. The more prevalent techniques include the use of synchrotron radiation-based techniques.[23] This is to achieve an analysis of the microstructure of underglazes and attempt in verifying and dating historical porcelains such as those of the Ming dynasty. This functions as a method to identify pigments and their origin. Such information is conducive to understanding the trade relations of nations at given times as pigments are sourced internationally and speak to the relationships between nations or empires. Differing cobalts used to colour underglazes in the Middle East and Asia regions were traded and that evidence can be found by inspecting the microstructures[24] of historic samples of pottery using these underglazes therefore supporting other archaeological data on the interactions of these cultures.

Notes

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Underglaze

View on Grokipedia
from Grokipedia
Underglaze is a decoration technique in which colored pigments or slips are applied directly to the surface of unfired greenware, leather-hard clay, or bisque-fired before a transparent or translucent glaze is added and the piece is fired in a , fusing the decoration beneath a protective glassy layer for enhanced durability and color intensity. This method allows for vibrant, permanent designs that resist wear, distinguishing it from overglaze techniques where colors are applied after the initial firing. The origins of underglaze trace back to in the late (618–907 CE), where the first high-fired stonewares with decoration under a glaze appeared around the second quarter of the at kilns in Gongxian, province, primarily for export to Near Eastern markets influenced by Mesopotamian styles. Production was short-lived domestically due to preferences for plain white or wares, but the technique evolved significantly during the (1279–1368 CE), with underglaze red using copper oxide and underglaze blue using imported becoming more widespread to meet export demands from and the Islamic world. By the (1368–1644 CE), underglaze blue-and-white reached its artistic peak, featuring intricate designs on high-quality white bodies, often for imperial and . The practice spread westward through the , influencing Islamic stonepaste ceramics in the and later European potters. In 18th-century England, potters innovated underglaze transfer printing around 1783, using engraved copper plates to mass-produce patterned earthenwares like blue designs, revolutionizing commercial ceramics. Underglaze materials typically consist of metal oxides—such as for blue, iron for brown or red, and for red or green—suspended in a clay slip with fluxes to ensure adhesion and color stability during firing at temperatures ranging from low-fire (around 1940°F) to high-fire (up to 2381°F). Common application techniques include brushing or painting freehand designs, (scratching through layered colors to reveal the clay beneath), mishima (inlaying pigments into incised lines), and modern transfers using newsprint or decals for precise patterns. These methods are versatile across clay types, particularly effective on light-colored bodies for sharp contrast, and remain essential in contemporary studio ceramics for both functional and sculptural works.

Definition and Principles

Definition and Process

Underglaze is a decoration technique that involves applying colored pigments or clay-based slips to the surface of unfired greenware or bisque-fired clay before covering it with a transparent glaze layer. These pigments, formulated with ceramic stains and metallic oxides, adhere to the porous clay body and become permanently embedded during firing, producing vibrant, durable designs that are visible through the overlying glaze. The core process begins with surface preparation, where the clay is typically at the leather-hard stage for greenware application or fully bisque-fired to create a stable, absorbent base that prevents the underglaze from running or blurring. Underglaze can be applied to greenware (leather-hard or bone-dry), in which case the piece is bisque-fired (typically 900–1100°C or 06–04) to set the decoration, followed by glaze application and a high-temperature glaze firing (1000–1300°C or 5–10). Alternatively, when applied to bisque-fired ware, the underglaze is followed directly by glaze application and a single high-temperature glaze firing (1000–1300°C or 5–10), during which the pigments mature and fuse with the clay matrix and glaze, forming a non-fading, integrated finish. In both cases, the underglaze is applied using techniques such as brushing, trailing, or inlaying, and allowed to dry partially to avoid smearing; the clear or transparent glaze is subsequently brushed, dipped, or sprayed over the decorated surface to seal and protect the colors. This approach distinguishes underglaze from overglaze enamel methods, which require an initial bisque firing, a high-temperature glaze firing, and then separate low-temperature firings (typically 700–800°C or cone 018–015) for the decorative enamels applied on top of the fired glaze, often resulting in more fragile surfaces prone to wear. In underglaze, the protective glaze layer shields the colors from abrasion and environmental exposure, enhancing longevity with no need for additional firings beyond the standard bisque and glaze sequence.

Advantages Over Other Decoration Methods

Underglaze decoration offers superior compared to overglaze methods, as the pigments fuse directly with the underlying clay body during the primary firing, creating a bond that resists abrasion, scratching, and wear far better than surface-applied overglazes, which can fade or chip under repeated use. This technique is also more cost-effective for production, requiring fewer total firings overall—typically two (bisque and glaze) when applied to greenware or one (glaze) when applied to bisque—compared to overglaze enamels, which demand three firings including an additional low-temperature step (cone 018–015) to fuse the decoration, increasing and time. Aesthetically, underglaze applied beneath a transparent glaze yields a uniform glossy finish with vibrant, opaque colors that maintain intensity without surface irregularities, making it particularly suitable for large-scale where consistency is essential. However, underglaze has limitations, including a restricted color palette limited to stable metal oxides that withstand high firing temperatures, such as for deep and for greens, as more vibrant hues like reds often require low-fire incompatible with or . Additionally, incompatible glazes can cause color bleeding, where pigments dissolve and migrate during firing due to mismatches. In comparison to or engobe techniques, underglaze enables finer, more precise detailing through brushwork or painting on leather-hard clay, avoiding the physical carving required in —which risks uneven lines—or the broader color coating typical of engobes, which lack the pigmentation for intricate designs. Modern commercial underglazes have expanded options beyond traditional oxides, incorporating stable stains for broader palettes while retaining these core advantages.

Materials and Preparation

Pigments and Colorants

Underglaze pigments primarily consist of metal oxides that provide stable coloration during high-temperature firing, with common examples including for intense blues, for reds and browns, and for greens. These oxides are typically mixed with fluxes, such as or alkaline compounds, to lower their melting points and ensure compatibility with the clay body and overlying glaze during . Cobalt oxide (CoO), derived historically from smalt or —impure forms produced by roasting cobalt ores and fusing with silicates—remains a staple for reliable hues in both traditional and modern underglazes. Manganese dioxide yields purples, particularly in low-alumina environments, while chrome oxide for greens faced limitations until the early due to challenges in its synthesis and stability, prior to which copper-based alternatives dominated. These pigments are prepared as liquid slips by suspending the oxides in with deflocculants or as dry powders for reconstitution, often incorporating binders like to enhance adhesion to leather-hard clay surfaces. , a natural gum derived from trees, is dissolved in hot (typically at a 1:2.5 ratio) and added to replace a portion of the mixing , providing temporary binding without affecting fired . During firing, the metal oxides vitrify and chemically integrate with the silica in the overlying glaze, forming stable that lock in color; for instance, cobalt oxide reacts in a simplified manner as CoO + SiO₂ → CoSiO₃, contributing to durable silicate structures. This integration ensures color permanence under typical 04–06 temperatures, with pigments applied via brushing or other methods prior to glazing.

Base Clay and Glaze Interactions

Underglaze compatibility varies significantly with , primarily due to differences in , firing temperature, and shrinkage rates. clays, typically fired at low temperatures (cone 010-04), exhibit high that enhances underglaze by allowing pigments to penetrate the surface, resulting in brighter colors and stable bonding during glaze firing. clays, fired around cone 6, have moderate and require underglazes formulated to match their higher shrinkage; mismatched formulations can lead to flaking if applied to leather-hard stages without sufficient binders. clays, also cone 6 compatible, demand thin underglaze applications due to their low absorption and high , ensuring even coverage without excessive drying cracks. Absorption rates play a critical role in underglaze , with bisque-fired clay (typically 10-25% absorption at 06-04) absorbing more liquid than leather-hard clay, potentially leading to uneven distribution if over-applied. Leather-hard clay, with lower absorption due to retained moisture, promotes better mechanical bonding as the underglaze shrinks uniformly with the body, reducing the risk of separation during or firing. Testing absorption via simple weight-gain methods on test tiles helps predict success across clay types. Glaze selection is essential for underglaze visibility and durability, with transparent lead or feldspathic glazes preferred as they allow pigments to show through without alteration, maintaining color fidelity on or bases. Matte glazes, while compatible, introduce a textured surface by diffusing light and reducing gloss, though they may dull vibrant underglaze hues if overly opaque. Fluid-melting transparent glazes, such as those based on frits, are recommended over and to prevent micro-bubbling that clouds underglaze colors. Mismatched thermal expansion between underglaze, clay, and overglaze can cause defects like crawling, where the glaze pulls away from the surface due to poor or high surface tension in the melt. This is exacerbated in low-fire if the underglaze lacks sufficient , leading to incomplete bonding; prevention involves adjusting the glaze or underglaze with fluxes or deflocculants to improve , flow, and compatibility. Pinholes, small gas vents in the fired surface, arise from trapped organics in the clay body escaping through the underglaze layer during glaze firing, particularly on porous bisque; extending the firing soak at peak temperature (up to 2 hours) allows gases to escape before the glaze seals. Small-scale test firings on compatible clay tiles are standard for identifying expansion mismatches early. Fluxes in underglaze formulations, such as or additions, ensure melting behavior aligns with the overlying glaze, promoting uniform fusion and minimizing defects like crawling on or . acts as a powerful low-temperature to lower the , while provide stable glass formation that matches clay rates, enhancing overall compatibility.

Historical Development

Ancient Origins in Egypt and Faience

The earliest evidence of underglaze-like techniques in dates to the New Kingdom (c. 1550–1069 BCE), where production incorporated pigments applied to -based bodies prior to glazing, laying the groundwork for later decoration methods. , a non-clay material, consisted of a paste body (92–99% silica, with 1–5% lime and 0–5% soda) formed through molding or hand-shaping, often using open or multi-part molds for of items such as beads, amulets, and inlays. pigments, yielding characteristic blue-green hues, were mixed into the glaze slurry or applied directly to the dried body surface before the glazing process, creating a self-glazing effect during firing. This approach, distinct from true clay glazing, relied on alkali fluxes like or plant ash to form a vitreous surface, with objects fired in kilns at 800–1000°C to achieve without melting the quartz core. Key production sites during the New Kingdom included the workshops at (c. 1353–1336 BCE), where archaeological evidence reveals specialized facilities for alongside glass and stoneworking, producing devotional items like ring beads, figures, and architectural tiles for temples and tombs. At 's O45.1 site, molds and structures indicate efflorescence glazing as the dominant technique, where alkali salts migrated to the surface during drying and firing to form the colored glaze layer over any applied pigments, though direct application of pigment slips to mold-pressed forms also occurred for decorative details. These techniques peaked in the 18th Dynasty, with objects often featuring or blue-green surfaces from copper-based colorants (1–2.5 wt% CuO), sometimes accented with for black outlines or for yellow tones. Firing in ovoid or round , without saggars in this period, allowed for efficient production of small-scale items like (servant figures for the ) and glazed tiles depicting religious motifs. By the Ptolemaic Period (332–30 BCE), techniques evolved to include more explicit underglaze layers, particularly in vessel production at sites like Memphis (Kom Helul), where a distinct underglaze of finer and pigments was applied to the body before the overlying alkali glaze. This layered structure— body, colored underglaze (often from ), and transparent or tinted glaze—enabled effects, as seen in Hellenistic-influenced bowls and figurines fired at around 1000°C for the body and 700°C for glazing, using saggars to stack items and prevent adhesion. Pigments remained -dominant for blue-green, but and were increasingly used for deeper blues and details, applied via to mold-formed pieces like amulets and beads. This refinement marked a transition toward true underglaze in glazed during and influenced subsequent Islamic traditions in glaze chemistry and application.

Asian Innovations in Porcelain and Islamic Pottery

The development of underglaze techniques in began in during the late (618–907 CE), with the first high-fired stonewares featuring decoration under a glaze appearing around the second quarter of the 9th century at kilns in Gongxian, province. In the (1279–1368 CE), Chinese potters at pioneered the use of underglaze decoration on white , marking a significant innovation in artistry. This technique involved applying oxide directly onto the unfired body before glazing and high-temperature firing, producing durable, vibrant blue designs on a translucent white ground. The pure white body, achieved through the use of kaolin clay, allowed the to penetrate slightly, creating a characteristic "heaped and piled" effect due to the imported pigment's iron content. Official kilns in scaled production for export across and beyond, facilitated by the Mongol Empire's trade networks. During the Ming Dynasty's Xuande era (1426–1435 CE), artisans refined underglaze techniques by incorporating imported Persian , which yielded a clearer, more stable blue hue compared to domestic sources. This , high in iron and low in manganese, was mixed with local pigments to mitigate the "bleeding" effect—where the color diffused undesirably during firing—while preserving aesthetic vibrancy. The innovation elevated porcelains to imperial standards, with examples featuring intricate floral and narrative motifs under transparent glazes. Such advancements reflected court-driven experimentation, positioning Xuande wares as pinnacles of blue-and-white . Ming Dynasty potters also developed underglaze copper red, known as cuivre rouge, as a complementary innovation to . This technique applied to the body before glazing, firing in a low-oxygen reduction atmosphere to achieve a dense, raspberry-red tone symbolizing imperial ritual significance. Exemplified in ritual dishes from the Xuande period, the color's rarity stemmed from firing challenges, where oxygen variations could yield greens or blacks instead; successful pieces featured subtle glaze bubbles enhancing texture. This marked an expansion of monochromatic underglaze palettes, influencing later developments. In the Islamic world from the 9th to 16th centuries, Persian potters advanced underglaze techniques with single-color blue-and-white styles on , imitating Chinese imports while adapting local motifs. Using under tin-opacified white glazes, artisans in regions like western produced vessels with geometric and vegetal designs, as seen in 9th–10th-century bowls excavated at . These wares, traded along the Silk Route, highlighted cultural exchange, with sourced regionally to create luminous effects on durable bodies. By the Timurid period (14th–16th centuries), such featured interlaced motifs in , bridging Abbasid traditions and later Safavid refinements. Ottoman Iznik pottery, flourishing from the 15th to 17th centuries, introduced quartz-paste bodies—fritware composed of ground , white clay, and —for superior whiteness and translucency in underglaze decoration. Early pieces (1480–1520) employed on white grounds, evolving by the 1520s to include (copper-derived) for " ware." In the late 1530s, manganese-based joined the palette alongside blue and , enabling complex, naturalistic floral and arabesque designs on tiles and vessels. This underglaze approach, fired at lower temperatures than , supported monumental architectural applications in mosques and palaces. Trade networks profoundly impacted these innovations, with from the region's Qamsar mines in central supplying both Persian and Chinese production from the Yuan through Ming eras. Historical accounts, including those by 14th-century scholar Kashani, describe ore processing into "lajvard" pigment for blue glazes, exported via Route caravans to . This influx enabled the Yuan's initial cobalt experiments and Ming's refined imports, fostering stylistic evolutions like Persian-influenced motifs in Chinese wares. The source's asbolane and ores provided consistent quality until local Chinese mining supplemented supplies in the .

European Advances in Earthenware and Transfer Techniques

In the 16th and 17th centuries, European potters adapted tin-glazed techniques, producing in and in the and , where blue underglaze motifs became a hallmark decoration. These wares consisted of red-firing bodies coated with an opaque white tin-oxide glaze, onto which cobalt-based blue pigments were applied before a final low-temperature firing, creating durable, imitation-Chinese effects often featuring floral, figural, or landscape designs. This underglaze approach, which emerged prominently in Dutch around 1625, allowed motifs to fuse with the body beneath the protective glaze layer, enhancing longevity compared to overglaze methods. Inspired briefly by Chinese blue-and-white imports, English potters advanced underglaze decoration from the 1760s through innovations in transfer printing on bodies like Wedgwood's and pearlware. contributed to the foundational cream-colored in the 1760s, providing a refined, lead-glazed body suitable for printed designs, though initial transfer experiments were overglaze. The breakthrough in underglaze blue transfer printing occurred around 1783–1784, pioneered by Josiah Spode using engraved copper plates inked with cobalt oxide pigments; the design was printed onto , transferred to the unfired clay surface, and fixed during high-temperature biscuit and glost firings, enabling efficient, repeatable patterns for and tiles. This technique expanded in the late to underglaze effects in , incorporating metallic oxides such as chrome for greens, iron for reddish-browns, for , and for purples, applied directly to the clay before glazing to achieve vibrant, stable colors under a single firing. Prattware, developed around the 1780s–1790s, exemplified this multi-color underglaze approach on relief-molded , featuring press-molded forms with raised classical, rustic, or animal motifs painted in underglaze hues and produced in large quantities for export to markets in America and . These wares, often attributed to potters like the Pratts of , prioritized bold, economical decoration over fine , supporting the region's industrial-scale output. By the , underglaze techniques on European declined as potters favored overglaze enameling on and , which permitted brighter, low-temperature colors and intricate detailing without the color limitations of high-fired underglazes. Tin-glazed production waned amid competition from these advanced bodies, shifting focus to enamel-decorated fine wares in factories like and .

Application Techniques

Direct Painting and Slip Methods

Direct painting and slip methods involve manual application of underglaze onto unfired clay surfaces, allowing artists precise control over decorative motifs and textures. These techniques are applied to leather-hard or bone-dry clay bodies, where the underglaze adheres before a transparent glaze is added and the piece is fired. In fine china production using porcelain, underglaze decorations are often painted directly onto the unglazed bisque-fired body before the clear glaze is added and the piece is fired, resulting in a smooth, glossy finish over the entire surface. Slip trailing, a fundamental method, entails pouring or piping colored slips—thicker suspensions of clay mixed with underglaze pigments—through a or bulb syringe to create raised lines, outlines, or filled areas on leather-hard clay. This process builds dimensional patterns that retain their form during drying and firing, enhancing tactile and visual interest in the final piece. Brush painting employs fine brushes to apply liquid underglaze directly onto the clay surface, enabling intricate motifs such as floral designs or landscapes. Artists often layer multiple coats of underglaze, starting with lighter colors and progressing to darker ones, to achieve depth and opacity; each layer must dry partially before the next to prevent . This method suits detailed work on curved forms like vases or plates, where can vary in pressure for subtle gradients. Layering typically requires at least two to three applications for vibrant results, with firing temperatures around 1000–1100°C preserving the colors beneath the glaze. Sgraffito integrates underglaze by first applying one or more colored layers to the clay, then incising through them with tools like or loops to expose the underlying clay body or contrasting colors. This scratching technique creates sharp, etched designs that contrast vividly after glazing and firing, often used for linear patterns or textural effects. The depth of incision controls the reveal, with shallow scratches producing fine lines and deeper ones broader contrasts. Specialized tools expand these methods' versatility. Airbrushes deliver underglaze in fine mists for even coverage or soft , ideal for blending colors on larger surfaces without marks; compressors with adjustable ensure controlled application on bisque or greenware. Masking with resist involves applying to protected areas before underglaze , preventing and allowing clean reveals of the base clay after firing. These tools facilitate complex compositions, from subtle gradients to precise patterns. In historical contexts, direct underglaze painting emerged prominently in Chinese porcelain during the (1279–1368), where motifs were brushed onto white clay bodies before clear glazing.

Transfer Printing and Stenciling

Transfer printing represents a mechanical method for applying underglaze designs to ceramics, enabling precise replication of intricate patterns on clay surfaces before glazing and firing. In the traditional , an artist's design is engraved onto a plate, which is then inked with an underglaze such as cobalt oxide mixed in an oil-based medium. The excess ink is wiped from the plate's surface, leaving pigment only in the etched lines; a sheet of thin is pressed onto the inked plate to absorb the design. This inked tissue is subsequently placed face-down on the leather-hard or bisque-fired clay body, where it is rubbed firmly to transfer the pigment, after which the tissue is carefully peeled away. The decorated piece is then glazed and fired at high temperatures, fusing the underglaze into the clay for durability. Stenciling offers another mechanical approach for underglaze application, utilizing templates to guide placement and achieve repeatable motifs. Cut-paper or silk-screen are positioned on the clay surface, creating masked areas that prevent pigment adhesion; underglaze is then applied through the openings via dusting, sponging, or brushing to deposit color selectively. Once the stencil is removed, the piece undergoes glazing and firing to set the design permanently. This technique, rooted in practices from Japanese surie methods, allows for bold, geometric patterns but requires careful alignment to avoid misalignment on curved forms. The evolution of transfer printing progressed from late 18th-century engraved copper plates, pioneered in English production around 1783–1784 at sites like and including , to 20th-century lithographic decals for greater efficiency. By the late , enabled multi-color printing on papers coated with underglaze fluxes, which could be soaked in water and slid onto clay surfaces, streamlining compared to labor-intensive plate . This shift, commercialized by firms like Syracuse China in 1896, reduced costs while maintaining fine detail. These methods excel in providing uniformity and for mass-produced ceramics, allowing consistent designs across large quantities without the variability of hand-painting. However, challenges persist with ink adhesion, particularly on absorbent clay or during tissue transfer, where incomplete bonding can lead to smudging or loss of fine lines during rubbing or firing.

Modern Uses and Innovations

Contemporary Studio and Industrial Applications

In contemporary studio , underglaze remains a versatile medium for artists seeking vibrant, durable decoration on complex forms. , a pioneering figure in American ceramics, frequently incorporated underglaze into her works, such as in her pieces combining underglaze with glaze and gold enamel to achieve layered, abstract patterns that blurred the lines between and . This approach allowed for bold color integration on curved surfaces, influencing modern potters who use underglaze to explore sculptural abstraction. Low-fire underglazes, firing at cone 06-04, have gained popularity in studios for their compatibility with clays, enabling faster production cycles and reduced energy use while maintaining opacity and resistance to bleeding under glazes. Educational applications of underglaze emphasize accessibility for beginners, with pre-formulated kits serving as essential tools in ceramics classrooms. Speedball's Underglaze Deluxe School Pack, containing 12 opaque liquid colors in 16-ounce bottles, is widely adopted in school settings for its non-toxic, non-bleeding properties ideal for techniques like sgraffito and detailed painting on greenware or bisque. Similarly, the Fuseworks Beginners Ceramic Underglaze Kit provides step-by-step instructions and supplies for introductory projects, fostering hands-on learning in community workshops and K-12 art programs. These kits support curriculum goals by allowing students to experiment with color layering without advanced equipment, promoting skill development in surface decoration. In industrial contexts, underglaze enhances the aesthetic and functional qualities of mass-produced ceramics, particularly in tile manufacturing where it provides hygienic, durable finishes. Opaque underglazes are applied to clay bases in ceramic tile production to create , textured surfaces that withstand high-traffic environments, often combined with transparent glazes for added protection against wear and moisture. For sanitary ware, such as basins and fixtures, underglaze decoration ensures bright, non-porous that meet standards, with meticulous application preventing defects like pinholes during glazing. These applications leverage underglaze's stability in large-scale firing processes, contributing to consistent output in facilities producing everyday durable goods. Post-2000 trends have seen underglaze integrated with digital fabrication methods, including , to produce innovative textured layers in ceramics. Researchers and artists have explored combining underglaze with to apply colored slips directly onto printed clay structures, enabling complex, customizable designs that revive historical transfer techniques in modern contexts. This fusion supports in studios and industries, expanding underglaze's role beyond traditional hand-application to and functional prototypes.

Commercial Products and Artist Adaptations

Commercial underglaze products are widely available from established brands such as Amaco and Mayco, which provide pre-mixed formulations in over 20 colors each, including non-toxic and low-fire variants suitable for educational and studio use. Amaco's Velvet Underglazes feature at least 31 colors, such as Ivory Beige and Terra Cotta, and are AP non-toxic, firing reliably from 05 for low-fire applications on greenware or bisque. In 2025, Amaco expanded its Velvet Underglazes with four new colors, continuing innovation in accessible formulations. Mayco's Fundamentals line offers versatile, blendable colors like Leaf Green and , certified AP non-toxic and dinnerware-safe with a clear glaze overcoat, firing from 06 to 10 with consistent performance across and . Contemporary artists have adapted underglazes for innovative applications, including screen-printed decals on rice paper or newsprint for precise custom designs transferable to leather-hard clay surfaces. This technique, borrowed from , allows for intricate patterns and repeatable motifs in decoration. Additionally, artists mix underglazes with engobes to create layered, textured effects, such as distressed or weathered surfaces, enhancing depth and visual interest in functional and sculptural pieces. Innovations in underglazes extend to like metallic finishes, with products such as gold underglaze enabling luminous, reflective surfaces in contemporary when fired from cone 06 to 9. British artist employs underglaze colors alongside photographic transfers and lustres in his 21st-century vessels, blending narrative motifs with vibrant, durable decoration. These underglazes support single firing for efficiency in studio practice when applied to greenware. The market for underglaze products has seen increased availability through online suppliers since the , aligning with broader growth in the ceramics sector at a 4.4% CAGR from 2025 onward, driven by demand for accessible art materials. Reputable platforms like Bailey Pottery and The Ceramic Shop now offer extensive selections from multiple brands, facilitating wider adoption among artists and educators.

Scientific Analysis and Authentication

Compositional Studies of Pigments

Compositional studies of underglaze pigments have primarily focused on cobalt-based blues, employing non-destructive analytical techniques to elucidate historical sourcing, manufacturing processes, and chemical evolution. (XRF) spectroscopy is widely used to detect trace elements, such as , which distinguishes Persian imports (high in ) from Chinese native sources (low in but rich in manganese and iron). For instance, portable XRF analyses of 16th–17th century Chinese porcelains reveal high concentrations in early Ming glazes, indicating reliance on arsenic-rich Persian cobalt ores, while later samples show below detection limits, signaling a shift to local asbolane ores. Complementing XRF, identifies molecular structures and phases, such as tetrahedral Co²⁺ ions in cobalt aluminate (CoAl₂O₄), confirming their role as the primary in underglaze blues. Key studies on (1368–1644) porcelains demonstrate import dependencies through , a roasted sourced from Persian mines and processed into a usable form for underglaze decoration. (SR-XRF) analyses of 39 Ming and three Yuan samples quantify elemental ratios like Fe/Mn, revealing high in zaffre-derived pigments (Mn/Co > 1), which correlate with imported materials during the early Ming period. Further, (SR-XRD) enables precise phase identification, detecting CoAl₂O₄ crystallites with lattice a ≈ 8.11 Å in Qinghua blue decors, where substitution affects lattice spacing and color intensity. These techniques highlight zaffre's role in achieving stable blue hues, with particle sizes of 1–5 μm distributed near the body-glaze interface. The evolution of underglaze pigments transitioned from natural mineral ores to synthetic oxides in the , driven by industrial advancements in . Prior to this, pigments relied on impure natural cobaltites like or , often contaminated with and , limiting color purity. In 1802, Louis Jacques Thénard synthesized pure cobalt aluminate (CoAl₂O₄) via of and aluminum oxides at high temperatures (around 1000°C), yielding a stable, arsenic-free suitable for underglaze applications in modern ceramics. Quantitative analysis in such studies often employs XRF peak intensities for cobalt concentration, following the relation: %Co=ICok×Cstd\% \text{Co} = \frac{I_{\text{Co}}}{k} \times C_{\text{std}} where ICoI_{\text{Co}} is the measured peak intensity, kk is the calibration factor derived from standards, and CstdC_{\text{std}} is the reference concentration, enabling precise sourcing without sample destruction. These compositional insights also aid briefly in distinguishing authentic historical pieces from forgeries by tracing elemental signatures.

Detection of Forgeries and Provenance

Modern forgeries of underglaze ceramics, particularly Chinese blue-and-white from the , often involve replicas produced in contemporary workshops that employ synthetic pigments to imitate the appearance of historical pieces. These fakes, frequently made in or other regions, use industrially refined lacking the characteristic impurities of ancient imported ores, resulting in brighter blues without the typical "" effect or iron spots seen in genuine wares. Detection of such forgeries relies on identifying anomalies in material composition through scientific techniques. Lead isotope ratio of glazes can reveal discrepancies, as historical lead sources exhibit specific isotopic signatures tied to regional ores, whereas modern fakes often show ratios inconsistent with pre-20th-century sites due to recycled or synthetic materials. Microprobe , such as electron probe microanalysis (EPMA), detects anachronistic elements like in pigments, which were unavailable or unused in traditional underglaze formulations before the . Provenance tracing links underglaze artifacts to specific historical workshops by matching elemental signatures in the cobalt pigments. For instance, Xuande-era (1426–1435) wares from frequently incorporate low-manganese, high-iron imported from in Persia, identifiable through ratios like Mn/Fe < 0.35 that distinguish it from later native Chinese sources (high Mn/Fe). This method establishes authenticity by confirming the global trade networks reflected in the pigment's geochemical profile. Case studies from the 20th and 21st centuries highlight the role of portable (pXRF) in exposing market floods of fakes. Analysis of suspected Ming-style blue-and-white pieces has revealed modern high-purity with elevated or levels atypical of Yuan-Ming imports, as seen in examinations of auction lots where pXRF distinguished replicas from genuine Xuande prototypes. Similarly, imitations mimicking Ming aesthetics, identified via on-site pXRF, showed synthetic traces and glaze inconsistencies, enabling rapid without invasive sampling.

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