Lustre

Written by John Kuczwal. Posted in Home

By lustre I mean reduced pigment or clay paste lustre. Sometimes called “Arabian”, “Persian”, or even "smoked lustre", its origins can be traced to the Middle East and the 9th century AD. It is thought that the technology had developed from glass workers who had discovered that metal oxides could be used to stain glass.  The alkaline and lead based glazes in use at the time were receptive to the formation of lustre.

As an expressive medium lustre has defied large scale production methods.  There are good reasons why this is so. After the pottery has been made and glazed in a conventional way, it must then be subjected to an additional firing that carries a great risk of failure. Cipriano Piccolpasso statement that “oft times of 100 pieces of ware tried in the fire, scarce 6 are good” remains as true today as when the statement was made 500 years ago. 

It might be useful to explain the practical side of lustre firing for those interested in exploring the technique. The already glazed and fired pottery is painted with a clay paste pigment (containing silver or copper metallic salts) and subjected to the right temperature, degree of reduction and duration of firing in this third and most critical firing (the lustre firing). Somewhere between 550 to 650 degrees C the glaze begins to soften and  becomes receptive to the formation of lustre. At these temperatures, a dull red glow becomes visible in the kiln and well before the discovery of heat measuring equipment, a kilns temperature was determined by eye and firing experience. The ions in the glaze and pigment are becoming excited and energised by the rising firing temperature. As the kilns atmosphere is reduced, the ions in the glaze and the lustre pigment begin to exchange and the metallic ions migrate into the glaze structure and reform themselves as metal. This all happens at the nano scale.  The ceramic term "reduction" means that oxygen entering the kiln is cut back (reduced) and is a simple thing to do by closing down the chimney damper. The reduction cycles will vary according to the kiln used for the firing and its size. In a traditional updraft wood kiln in use both by the Islamic world and later during the Renaissance in Italy, a small number of reduction cycles were used (as little as perhaps 2 or 3) whilst in a modern day downdraft wood kiln it maybe upwards of 9 or so reduction cycles. The formation of a red lustre  (based on copper salts) favours slightly higher temperatures and a longer reduction cycle.

Visible in the illustration from the Piccolpasso manuscript is the sand timer as the kiln firer regulates the cycles and the duration of the firing. 

The only true governing factor in determine the correct number of firing cycles is that the firing should end as soon as the lustre colour sought has formed, determined by examining draw trials that are removed from inside the kiln after each reduction cycle.The total duration of these reduction cycles is rarely longer than an hour or so as the lustre pigment is slowly being volatilised away. Too low a temperature (the glaze has not softened sufficiently) and the clay pigment is easily brushed away to show that no lustre has formed underneath the pigment crust; too high a temperature, or too strong a reduction cycle or that a reduction cycle has been too long in duration and the work is ruined as the clay pigment carrier fuses into the glaze and cannot be removed and the pigment has over-fired and darkened to a dark matt stain.

There is a small window of opportunity when the glaze and pigment (after heating to the right temperature) become receptive and a film of lustre is able to be deposited into the glaze.

This type of lustre differs from resinate lustre (an 18th century invention and nowadays the most common form of lustre used on ceramics) where the film of metal is deposited onto the glaze and as such is easily abraded by wear.

Analysis by electron microscope reveal that lustre forms at a nano level with the transference of ions from the metal oxide pigment into the receptive glaze. The metal oxide on this nano scale is laid down in layers with each reduction cycle, and as light passes through these layers, interference and the refraction of light occurs, being  reflected back through these layers and so producing those iridescence colours we can see in a rainbow. And just as with a rainbow, the colours appear to change as the viewing angle is changed.

To be present at a lustre firing, when the exit for the flame is closed shut (almost), one sees smoke seeping out of every crack in the kiln, changing from black to white to acrid yellow as the oxygen is stolen from inside the kiln by the reducing atmosphere (see the illustration from Piccolpasso's manuscript). The kilns draught is slowed further and if one peers inside, smoke is seen to flow under and over, hovering over depressions of the painted pottery before finally exiting wherever it can from the kiln. It is in these quiet areas of the kiln that the most interesting of colours and iridescence develop. 

Lustre making can rightly be described as painting with smoke.

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Lustre Pottery

Written by John Kuczwal. Posted in Home

By lustre I mean reduced pigment or clay paste lustre. Commonly called “Arabian”, “Persian”, or even "smoked lustre", its origins can be traced to the Middle East and the 9th century AD. It is thought that the technology may have developed from glass workers who had discovered that metal oxides could be used to stain glass.  The alkaline and lead based glazes used at the time are receptive to the formation of lustre, as were the naturally reducing updraft kiln designs but it still required the discovery and development of a specialized firing technique to advance the technique.

Lustre Bowl, Kashan, Iran Seljuk period 12th Century AD

The earliest lustre was believed to have been made in or around the region in what is now known as Iraq in the early 9th century.  A time of shifting Caliphates and centres of power as well as the rise in demand for luxury goods (including stoneware and porcelain ceramics imported from China) contributed to a climate where pottery workshops were experimenting and developing new techniques including tin-opacified glazes, underglaze painting, on-glaze enamels (minai), gold leaf on-glaze decoration (lajvardina) and lustre ceramics. The lustre technique was the most difficult to control, its first makers having inherited knowledge from glass workers using the oxides of silver and copper to apply line decoration and colouring glass. This knowledge of decorating glass was likely responsible for the discovery that lustre can also form on a receptive ceramic glaze.

As the centres of power shifted through the capitals of the Middle East, tin glazed ware (maiolica) and lustre spread into Europe via the Iberian peninsula (modern day Spain) possibly as early as the 11th century. Major production centres included Malaga and later Manises.

Manises Spain 1550-1610

In the 14th and early 15th century, lustreware from Spain found a receptive market in Italy and was soon being made in the ceramic centres of Deruta and Gubbio, amongst others. Deruta was most probably the first town in Italy to begin to use the lustre technique through its connections with the Vatican and the lustre potters of Valencia. The Renaissance potters used the gold and red lustre colours in their magnificent istoriato paintings. The making of maiolica spread into other European countries, in France coming to be known as faience and in the Netherlands as delftware.

Special mention must be made of the workshop of Maestro Giorgio Andreoli of Gubbio that prospered until 1536 when he handed it over to his son. Much of the work was made by others and elsewhere but lustered in his workshop.  At its best, the deep ruby red lustre has to this day never been bettered.

Perhaps because it is such a difficult and unpredictable process or perhaps because of a change in taste or fashion, the making of reduced pigment (clay paste) lustre fell into decline.

Driven by a desire to copy the masterworks of the Renaissance cinquecento, a revival in the making of lustre took place in the late 19th and early 20th centuries in locations such as Deruta, Pesaro, Gualdo Tadino and Gubbio.

Paolo Rubboli "Massinissa in the Palace of Sophonisba"(1875-80) Gualdo Tadino

It was also given new life in individual studio workshops by men such as William De Morgan (England) Pilkingtons (Royal Lancastrian Pottery)(England), Vilmos Zsolnay (Hungary) and Clement Massier (France). These workshops also experimented with resinate lustre (a predictable form of lustre that may be fired in oxidation and suited to large scale production) and in-glaze lustre. Resinate lustre because of its predictability came to dominate production lustre making.

Alan Caiger-Smith "The Dance"  1998 Aldermaston England

Alan Caiger-Smith and the Aldermaston Pottery in England played a pivotal role in re-introducing pigment lustre to the English speaking world. His book "Lustre Pottery: Technique, tradition and innovation in Islam and the Western World" remains important in explaining in practical terms how it is made and charting its history.

In Australia, Alan Peascod following a chance meeting with an Egyptian potter from Fustat, Said El-Sadr, began to use the technique and in his role as teacher, innovator and as a maker of lustre, advanced the tradition.

Alan Peascod 1994 Wollongong Australia

Scattered around the world, there continues to be a handful of potters that use this most challenging of ceramic techniques, that of reduced pigment or clay paste lustre.

It is the technique I use in my work. A description of the technical aspects follows on the next page with additional information and images at   http://www.johnkuczwal.com

John Kuczwal "Moonlight" Reduced Pigment Lustre on porcelain 2017 

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