The use of ash after Saggar Firing: Hasan Baskirkan describes an alternative raw material for glazes.
Stacked lidded boxes made of refractory clay were first used in China when firing celadon glazes on porcelain bodies (Figures 1-2), protecting the products from flyaway ash, reducing and the atmosphere that occurs in gas furnaces. The first celadon porcelains were produced during the Sung Dynasty in China in 1000 AD (960-1280 AD). The use of saggars was developed as an important invention as a result of firing porcelain products that were biscuit fired and produced for the Sui and Tang monarch dynasties in China. In this way, it was possible for high quality celadon to be produced and fired in large and high kilns. The production of saggars can be seen in the period of Southern Sung Royalty ceramics.
During the glaze firing in saggar boxes in China, when the glaze fluxed, most of the products and saggar boxes were damaged. To prevent saggar boxes and products from being damaged, small coasters were placed under the ceramics for the fluxing of glazes.
Sung Kilns (highly developed Chinese kilns used today) were usually built on a hill and made up of stepped levels up to 50 metres long. Ceramic firing kilns were described by Chinese authors as large dragons that spread flames. Although coal was used in much smaller kilns, most of the kilns were fired with wood. Potters had to solve the problem because they knew that the uncontrolled ash damaged the celadon glaze. (Figure 3). By means of Longchuan ceramics kilns, about 20,000 ceramic works could be fired at one time in saggar boxes (4).
The first potters to use saggar boxes discovered that the evaporated parts of the glazes that were used formed a glassy structure on the inner parts of the saggars. The transfer formed through evaporation occurred as the return of the smoke faced the inner walls of saggars on the product. As a result of this, research potters started to use the aforementioned reaction to improve techniques (3).
2. Sawdust is described as "Tiny particles of wood, iron processed by tools such as saws while shaving, filing, lathing or cutting" (5). Sawdust is often used for the production of particleboard, in stoves as solid fuel and as ground in the hovels where barnyard fowl live.
Copper is in the first sub group of the periodic table (in Group IB) and is represented with 'Cu', it has 63.54 grams of molecular weight. Its atomic number is 29 and has the atomicity of + I and + II. Although copper moves freely in nature in small quantities, it exists especially as red cuprite [Cu.sub.2]O, halkosit [Cu.sub.2]S, gold-bright halkopirit CuFe[S.sub.2], bornit [Cu.sub.3]Fe[S.sub.3], bright-green malachite [Cu.sub.2][(OH).sub.2]C[O.sub.3] and dark blue azurite [Cu.sub.3][(OH).sub.2][(C[O.sub.3]).sub.2] in nature (6). Copper may have the atomicity of I and II in its compounds. Copper (I) oxide, [Cu.sub.2]O is red and copper (II) oxide, CuO is black. Copper (I) salt is unstable, it can turn into copper (II) salt in the air easily. Copper (I) salt does not usually dissolve in water. Copper (II) salts such as nitrate, sulphate and their chlorides dissolve easily in water. Copper halide is volatile and colours the flame green. Copper sulphate is represented as CuS[O.sub.4].
Nickel is in the eighth sub group of the periodic table (in Group VIII B) and represented with Ni, it has 58.71 grams of molecular weight. Its atomic number is 28 and has the atomicity of + II and +III. It exists primarily as pentlandit (NiFe)S and garnierite (Ni, Mg) Si[O.sub.3].x[H.sub.2]O in nature. Metallic nickel is silver white. It does not dissolve easily in sulphuric acid and hydrochloric acid, but it does so in nitric acid. Crystal shaped nickel salt is green, anhydrous salt is usually yellow. Most of the salt dissolves in water; though sulphur, carbonate and phosphate do not dissolve. Nickel sulphate is represented as NiS[O.sub.4] (6).
Cobalt, along with sulphuric acid, can be obtained by adding cobalt (II) oxide or cobalt (II) hydroxide into reaction. It is used as a pigment or to obtain other cobalt salts. Electroplating is also used for cobalt. It was used for the production of beer, as well; however, it is not used today when producing beer because cobalt (II) sulphate includes a toxic material and overusing is poisonous. It is a compound used in ceramics and it rarely exists naturally (7).
Boxes for saggar firing are made of chammotte clay which includes a high proportion of silica, aluminium oxide and coarse grained, broken ceramic pieces. Cylindrical boxes are formed by the plating method. The biscuit firing of dried saggar boxes is done in gaseous kilns at 1000[degrees]C. First, about 10 cm of pine sawdust was used to fill the bottom of the boxes and copper sulphate, nickel sulphate, cobalt sulphate, which are auxiliary materials for firing, were sprinkled on the sawdust. Forms on which copper wires were wrapped in different orders were stocked up on the pile carefully and extra sawdust and metal salt were added as layers. This process was repeated a few times. The sawdust was put on the upper parts of the boxes and the gaps of the lids of the boxes were tightly slimed with chammotte clay. The firing process takes seven hours to complete. The approximate waiting period at the highest heating point (1000[degrees]C) was 10 minutes. The cooling of the gaseous kiln takes about 17 hours. After the kiln had gone completely cold, the saggar boxes were taken out of the kiln. Since the inner temperatures of the kiln and box were different, after the inner part of the box had been completely cooled, the lids were opened. The forms were carefully taken out of the boxes and the surfaces were cleaned with a dry sponge (Figures 4-5). Forms were varnished to polish the cleaned surfaces, to make the colours vivid and to make the forms have protective features. Then, the process was concluded by brightening the surface of the form with a velvet cloth (buckskin or a similar material can also be used) (8).
3. Ash Glazes: Ash can be described as the incombustible dusted residue of burned organic materials or incombustible elements of a burned substance. In short, ash is the name given to the metallic salt that is residue of organic (mostly herbal) substances. They have been continued to be used long after their accidental discovery (9). Ash glaze is formed on ceramic materials by glazing with just ash as described above or with different raw materials. Since the differences in these factors affect the qualities of the glazes, the purity of the material provided and the continuity of the supply is important in obtaining ash glaze (10).
Ash is collected in vast amounts, accumulated and mixed. Ash is sifted to cleanse it of unburned or unprocessed particles. Then it is soaked thoroughly in water. This process can be repeated to clean away resolvable substances (11). Some ceramists prefer dry ash cleaned of foreign substances without wetting, by using a fine sieve; in this way they preserve resolvable flux. The next step is to use ash in a glaze with increasing proportions. It is not right to establish regulations about the preparation of it since the ashes differ.
Ash glaze was first discovered accidently in the Shang Period in China in 1500 BC. Pots had the first glazed form with the discovery of ash glaze and had a persistent waterproof, glassy and aesthetical appearance (Figure 6). This new glaze was a glaze that was applied by brushes or dipping methods, or sifting the ash-clay mixture on the pots before placing the forms into kilns (12). Ash glazes were applied as an undercoat that included iron and oxidised to obtain a straw colour glaze in China during the 8th and 9th centuries (12).
4. Glaze Experiments with Saggar Ash: Ash was collected and accumulated after many saggar firings (Figure 7). First, it was ground and tried on biscuit bodies (Figure 8). Glaze recipes were composed in three groups. Groups of A and B glazes were prepared with colemanite, ulexite and raw and calcined saggar ash in conformity with the binary system. The ash proportion changed from 95 percent to 70 percent. Additionally, ash is used as a C group component for stoneware recipes. Recipes that are composed of saggar ash and ulexite are coded as A (uncalcined ash and ulexite) and AC (calcined saggar ash and ulexide); glaze recipes where colemanite is a flux are coded as B (raw ash and colemanite) and BC (calcined ash and colemanite); ash component stoneware recipes are coded as C (raw ash and stoneware glaze) and CC (calcined ash and stoneware glaze). Ash was calcined at 1000[degrees]C. Prepared recipes were weighed and ground wet by using a ball mill for 20 minutes, sifted by using 100 mesh sieves, applied to biscuit plates and fired in electric kilns at 1200[degrees]C for seven hours. The different effects were analysed by adding + 5 percent ZnO and + 5 percent TiO, (A Z, [A.sub.5]Z, [C.sub.2]Z, [C.sub.5]Z, [A.sub.2]T, [A.sub.5]T, [C.sub.2]T and [C.sub.5]T) separately to the [A.sub.2], [A.sub.5], [C.sub.2], [C.sub.5] recipes that were obtained. After all the experiments, it was decided that [A.sub.2], [A.sub.2]Z, A[C.sub.2] and A[C.sub.5] coded recipes were deemed fit to be used as artistic glazes and they were multiplied and applied on three-dimensional forms. It was observed that all the samples in the kiln had different colour and texture effects (Figures 9-10).
The results of the study showed that the ash obtained from saggar firing can be utilised as an alternative raw material for use in glaze composition. Even when just the ground raw ash is used on ceramic bodies, the glaze is formed at 1200[degrees]C. Flux was added to the ash and it was used in glaze compositions. It was observed that glaze that had been fired both on vertical and horizontal surfaces at 1200[degrees]C had both a metallic and matte glaze appearance which is an appropriate artistic effect. It is thought that what caused the metallic appearance is the metallic salt mixture that is added to the saggar boxes to colour the forms during firing and is composed of auxiliary materials such as copper sulphate, nickel sulphate and cobalt sulphate. It was observed that since the glaze is not liquid after firing, it can be used easily for three dimensional forms that were fired both vertically and horizontally.
As with all ash glazes, some difficulties occurred with this ash glaze. Because of the surprising results with glaze that was produced from the ash obtained from saggar firing, however, it was shown that it can be utilised artistically. It was confirmed that with the high proportion use of ash obtained from saggar firing artistic metallic glaze can be evaluated on its singular appearance.
(1.) Uzuner, O., (1994), "Diversity of Depending to Technique in Ceramic Art", Unpublished Master's Thesis, Anadolu University, Institute of Social Sciences, Eskisehir, Turkey.
(2.) Ay, N, Karasu, B, Erkmen, Z E, Kurama, S and Ozel, E. (1999), English-Turkish Ceramics Glossary, Anadolu University, Department of Ceramic Engineering, Eskisehir, Turkey.
(3.) Dassow, S. (2001), Barrel, Pit and Saggar Firing, A Collection of Articles from Ceramics Monthly, The American Ceramic Society, US.
(4.) Speight, C F. (1989), Hands in Clay, Mayfield Publishing Company Mountain View, California, US.
(5.) http://www.tdk.gov.tr/tdksozluk (Access Date: 08.03.2014).
(6.) Keskin, H, (1978), Analytical Chemistry and Chemical Problems, Fatih Printing Publisher, Istanbul University Press, Istanbul, Turkey.
(7.) http://simple.wikipedia.org/wiki/Cobalt%28II%29_sulfate (Access Date: 08.03.2014).
(8.) Baskirkan, H, (2010), "Smoke Firing Techniques", unpublished thesis proficiency in arts, Mimar Sinan Art University, Institute of Social Sciences, Istanbul, Turkey.
(9.) Genc, S, Baskirkan, H, Sarnic, O ve Agatekin, E, (2002), Investigation on Usage Sunflower Body and Tea Dregs Ashes in Ceramic Glazes in 1200[degrees]C, With International Participation V. Ceramic Congress, Proceedings Books, Istanbul, Turkey.
(10.) Genc, S, Baskirkan, H, Atay, C, Onaran, E, Sumengen O, (2002), Investigation on Usage Opium Poppy, Tobacco, Olive, Corncob and Straw Ashes in Ceramic Glazes on Red Fired Clay Bodies in 1000[degrees]C, II. International Eskisehir Terra Cotta Symposium, Proceedings Books, Eskisehir, Turkey.
(11.) Tichane, R, (1998), Ash Glazes, Krause Publications, US.
(12.) Rogers, P, (1991), Ash Glazes, England.
Hasan Baskirkan graduated from Anadolu University Faculty of Fine Arts Department of Ceramics in 1999, where he earned a masters degree in 2002 and earned a proficiency in art degree in 2010 from Mimar Sinan Fine Arts University Social Science Institute Department of Ceramic and Glass Arts. He is an Assistant Professor at Mimar Sinan Fine Arts University Faculty of Fine Arts Department of Ceramics and Glass Design. He was awarded the Youth Award at the 7th Gold Pot Ceramics Competition of Izmir Rotary Club and the Biennial Youth Award at the 6th Cairo International Ceramics Biennale, Ceramic Competitionin 2002; the Art Encouragement Award of Anadolu University in 2006 and the 70th Ministry of Culture Ceramics Competition Grand Prize in 2010. He has shown his work nationally and internationally. All photographs and ceramic forms by Hasan Baskirkan, unless noted.
Table 1. Saggar Ash-Ulexite and Calcined Saggar Ash-Ulexite Glaze Composition Examples (1200[degrees]C). Recipe Uncalcined Saggar Ash and Image No. Ulexite Glaze Composition Recipe (Percent) A1 70 Saggar Ash 30 Ulexite A2 75 Saggar Ash 25 Ulexite A3 80 Saggar Ash 20 Ulexite A4 85 Saggar Ash 15 Ulexite A5 90 Saggar Ash 10 Ulexite A6 95 Saggar Ash 5 Ulexite Recipe Calcined Saggar Ash and Image No. Ulexite Glaze Composition Recipe (Percent) AC1 70 Calcined Saggar Ash 30 Ulexite AC2 75 Calcined Saggar Ash 25 Ulexite AC3 80 Calcined Saggar Ash 20 Ulexite AC4 85 Calcined Saggar Ash 15 Ulexite AC5 90 Calcined Saggar Ash 10 Ulexite AC6 95 Calcined Saggar Ash 5 Ulexite Table 2. Saggar Ash-Colemanite and Calcined Saggar Ash-Colemanite Glaze Composition Examples (1200[degrees]C) Recipe Uncalcined Saggar Ash Image No. and Colemanite Glaze Composition Recipe (Percent) B1 70 Saggar Ash 30 Colemanite B2 75 Saggar Ash 25 Colemanite B3 80 Saggar Ash 20 Colemanite B4 85 Saggar Ash 15 Colemanite B5 90 Saggar Ash 10 Colemanite B6 95 Saggar Ash 5 Colemanite Recipe Calcined Saggar Ash and Image No. Colemanite Glaze Composition Recipe (Percent) BC1 70 Calcined Saggar Ash 30 Colemanite BC2 75 Calcined Saggar Ash 25 Colemanite BC3 80 Calcined Saggar Ash 20 Colemanite BC4 85 Calcined Saggar Ash 20 Colemanite BC5 90 Calcined Saggar Ash 20 Colemanite BC6 95 Calcined Saggar Ash 5 Colemanite Table 3. Saggar Ash-Stoneware Glaze and Calcined Saggar Ash-Stoneware Glaze Composition Examples (1200[degrees]C). Recipe Uncalcined Saggar Ash Image No. and Colemanite Glaze Composition Recipe (%) C1 70 Saggar Ash 6 Sodium Feldspar 6 Potassium Feldspar 9 Ulexite 6 Quartz 3 Kaolin C2 75 Saggar Ash 5 Sodium Feldspar 5 Potassium Feldspar 7.5 Ulexite 5 Quartz 2.5 Kaolin C3 80 Saggar Ash 4 Sodium Feldspar 4 Potassium Feldspar 6 Ulexite 4 Quartz 2 Kaolin C4 85 Saggar Ash 3 Sodium Feldspar Feldspar 4.5 Ulexite 1.5 Kaolin C5 90 Saggar Ash 2 Sodium Feldspar 2 Potasium Feldspar 3 Ulexite 2 Quartz 1 Kaolin C6 95 Saggar Ash 1 Sodium Feldspar 1 Potassium Feldspa 1.5 Ulexite 1 Quartz 0.5 Kaolin Recipe No. Calcined Saggar Ash Image and Colemanite Glaze Composition Recipe (%) CC1 70 Calcined Saggar Ash 6 Sodium Feldspar 6 Potassium Feldspar 9 Ulexite 6 Quartz 3 Kaolin CC2 75 Calcined Saggar Ash 5 Sodium Feldspar 5 Potassium Feldspar 7.5 Ulexite 5 Quartz 2.5 Kaolin CC3 80 Calci ned Saggar Ash 4 Sodium Feldspar 4 Potassium Feldspar 6 Ulexite 4 Quartz 2 Kaolin CC4 85 Calcined Saggar Ash 3 Sodium Feldspar 4.5 Ulexite 3 Quartz CC5 90 Calcined Saggar Ash 2 Sodium Feldspar 2 Potasium Feldspar 3 Ulexite 2 Quartz 1 Kaolin CC6 95 Calcined Saggar As 1 Sodium Feldspar 1 Potassium Feldspar 1.5 Ulexite 1 Quartz 0.5 Kaolin Table 4. Glaze Composition Examples of Additive with TiO2 and ZnO to Selected Recipes (1200[degrees]C) Recipe Recipe (%) Image No. A2T 75 Saggar Ash 25 Ulexite + 5 Ti[O.sub.2] A5T 90 Saggar Ash 10 Ulexite + 5 Ti[O.sub.2] C2T 75 Saggar Ash 5 Sodium Feldspar 5 Potassium Feldspar 7,5 Ulexite 5 Quartz 2,5 Kaolin + 5 Ti[O.sub.2] C5T 90 Saggar Ash 2 Sodium Feldspar 2 Potasium Feldspar 3 Ulexite 2 Quartz 1 Kaolin + 5 Ti[O.sub.2] A2Z 75 Saggar Ash 25 Ulexite + 5 Zn[O.sub.2] A5Z 90 Saggar Ash 10 Ulexite + 5 Zn[O.sub.2] C2Z 75 Saggar Ash 5 Sodium Feldspar 5 Potassium Feldspar 7,5 Ulexite 5 Quartz 2,5 Kaolin + 5 Zn[O.sub.2] C5Z 90 Saggar Ash 2 Sodium Feldspar 2 Potasium Feldspar 3 Ulexite 2 Quartz 1 Kaolin + 5 Zn[O.sub.2]
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|Date:||Nov 1, 2014|
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