In Flux

Kelsey Malone

I was seventeen when I started selling my ceramics, and was taken aback when one of my first customers asked if the pieces contained lead. The question seemed a little dramatic, directed at a teenager at a Seattle community fair, but it was not unwarranted. Lead has left a deep stain on ceramics, with fear of exposure to its toxicity gradually developing since it was first used in ancient times. 

Lead is a key ingredient in traditional low-fire earthenware glaze, which is formulated by balancing three components: a glass former, a stabilizer, and a flux. Silica is the most common glass former, less prevalent in low-fire formulas than higher-temperature stoneware and porcelain glazes. The stabilizer is often composed of powdered clay itself, and adjusts the glaze’s flow to prevent it from running off the piece when fired. The flux's primary role is to lower the glaze’s melting temperature and thus accelerate the rate at which it matures in the kiln. Lead is an ideal material for this purpose, because of its low melting point (Cone 022 or 1,000ºF), transparency, and high refractive index, resulting in a high-gloss, brilliant finish.

Early glazes were flux-dominant and prioritized melting at achievable temperatures. Alternative fluxes did exist, principally organic ash and alkaline salts, but lead's consistency and vibrancy were unparalleled. In the ancient Mediterranean – initially in Turkey, and then across the Roman Empire – and in China, lead glazes seem to have been developed independently. Initially, the goal was probably to waterproof utilitarian vessels, rather than for decorative purposes, but potters soon realized that in combination with the right colorants, lead could be used to create a spectacular palette, unlike anything seen before.

Examples of Roman lead-glazed wares include skyphoi (drinking cups) fired in provincial kilns, decorated using copper to make green and iron to create yellowish-brown. This same palette was also used, together with cobalt blue, on T’ang Dynasty sancai (three-color) earthenware – a profitable export along the Silk Road. In what it is today Iraq, potters of the Abbasid Dynasty developed the first examples of metallic luster glaze. Copper and silver oxides were adhered onto pre-glazed ceramics, then fused in a lead glaze without melting the precious metals. 

The last significant innovations in lead glaze were initiated by Josiah Wedgwood in England’s pottery capital, Stoke-on-Trent. A meticulous formulator, Wedgwood developed a low-fire imitation of Chinese porcelain for a fraction of the production cost. His lead-glazed “creamware,” perfected over the course of 5,000 trials, was marketed as England’s finest tableware, eventually under the name “Queen’s ware” after he was granted royal patronage. High demand for the product, however, exposed thousands of factory workers to lead-based glazes. 

Among many things, the Industrial Revolution was a giant experiment in materials. Unprecedented numbers of people were introduced to the same substances under the same conditions at the same time. Lead poisoning became much more difficult for ceramic manufacturers to ignore; physicians spoke of "potter's palsy," a malady of the nervous system. Factor workers tasked with glazing – so-called “dippers,” a role often reserved for young boys – had one of the most dangerous positions in production. In 1889, the UK Home Office reported a record high of 432 lead poisoning cases.

Finally, establishment figures began to take action. A district surgeon in Stoke-on-Trent, Dr. John Thomas Arlidge, drew on his own clinical practice in Hygiene, Diseases and Mortality of Occupations (1892), a 550-page report detailing cases of lead poisoning, and instances of “potter's phthisis,” a lung disease caused by inhaling glaze dust. Arlidge found that potters’ average life span was ten years shorter than the general population. His research was an influence on new regulations issued by the UK Home Office in 1898, which targeted lead exposure in pottery manufacturing by improving factory hygiene and implementing routine medical examination. Affected workers were removed before they became too sick, and illness rates were tracked at a larger scale. According to William Burton’s The Use of Lead Compound in Pottery, from the Potters’ Point of View (1899), lead poisoning cases in ceramic production decreased by more than 33% from 1898 to 1899. Awareness was increasing, conditions were improving; a leadless future was on the horizon.

Developing new glazes was an essential next step. William Furnival’s Researches on Leadless Glazes (1898) is a thorough compendium of recipes, often using borax as a flux alternative. In the introduction, Furnival emphasized the difficulty of replacing lead by quoting Josiah Wedgwood, who had written: “any interference with the amount of free lead in glazes would mean the absolute closing of one branch of our manufacturing… we have experimented for years with glazes, but have not succeeded in dispensing with lead in its raw state.” Eventually, though, a leadless version of his iconic Creamware glaze was indeed adopted, using feldspar frit for the flux; a mixture of medical research, government regulation, and technical innovation was essential in guiding industrial production to a safer future.

I make ceramics nearly every day. Lead does not play a physical part in my practice, but reminders of its toxic history are always ready to hand: "lead-free" is printed on every single storebought glaze bottle. Although lead has long been removed from the commercial market, its stigma remains; two millennia after it first entered ceramic history, making glazes bright, it still casts a dark shadow.