Underglaze
Underglaze is a method of decorating
Many historical styles, for example Persian
Examples of oxides that do not lose their colour during a glost firing are the
An
History
Ptolemaic faience
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
Through the
2O
4 (Jacobsite) rather than Fe
3O
4 (Iron(II,III) oxide
Faience
Most styles in this group, such as Delftware, mostly used blue and white pottery decoration.
Islamic world
Classical
English transfer printed earthenware
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
Initially most production just included one colour, but later techniques were developed for printing in several colours.
Current use
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
Underglaze transfers are a technique that involves screenprinting or free handing a pattern onto a transfer paper (often rice 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
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
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
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
- ^ Savage, 26-28
- ^ Savage, 26-28
- ^ Savage, 27
- ^ "走向世界的铜官-----湖南日报数字报刊". hnrb.voc.com.cn. Retrieved 2020-05-30.
- ^ Savage, 26
- ^ Savage, 29
- S2CID 191530630.
- ^ JSTOR 41674283.
- .
- ^ British Museum (2017). "Chinese porcelain: decoration". SmartHistory.
- S2CID 191572552.
- JSTOR 10.1525/j.ctt1pnfm7.
- ^ Savage, 95-97
- ^ Savage, 91-93
- ^ Hughes, 136
- ^ Hughes, 136
- ^ Hughes, 136
- S2CID 164148024.
- ISBN 978-0-387-33598-8. Retrieved 2021-06-22.
- ^ Jenssen, Victoria (2022). "16.Unsafe Studio Practice:Lead Poisoning". The Art of Carol Janeway: A Tile & Ceramic Career with Georg Jensen Inc. and Ossip Zadkine in 1940s Manhattan. Friesen Press. p. 199-206.
- ^ "How to Get Stunning Results with Underglaze Transfers". The Art of Education University. 2019-05-01. Retrieved 2020-06-26.
- S2CID 154437011.
- S2CID 206900979.
- PMID 27251853.
References
- Fournier, Robert, Illustrated Dictionary of Practical Pottery (Van Nostrand Reinhold, 1973) ISBN 0-442-29950-8
- Hamer, Frank, and Hamer, Janet, The Potter's Dictionary of Materials and Techniques (A&C Black/University of Pennsylvania Press, 2004) ISBN 0-8122-3810-9
- Hughes, G Bernard, The Country Life Pocket Book of China, 1965, Country Life Ltd
- Savage, George, Pottery Through the Ages, Penguin, 1959