ĀHAK

 

ĀHAK “lime,” a solid, white substance consisting essentially of calcium oxide.

i. Production.

ii. Early use of lime mortars.

i. Production

Calcium oxide is produced by heating limestone and other forms of calcium carbonate to a temperature of more than 900° C (referred to as lime burning). Thereby carbon dioxide (CO2) is released from the carbonate. In commercial processing pieces of natural limestone are heated in a charcoal kiln to a temperature of 900-1,200° C. Several different types of kiln are used; the shaft furnace, which is similar to the rudimentary, traditional type of kiln used in Iran and elsewhere, has a vertical brick shaft in which limestone and combustible material (charcoal, coke, or, in Iran, usually wood) are mixed together or packed in alternate layers. The mixture is constantly replenished from above and sinks down as the burnt lime is removed from below. In the process limestone loses up to 44 per cent of its weight and 13-15 per cent of its volume. Various fuels may be used—the upland shrubs Artemisia herba alba, A. santonica, and A. maritima; wood in forested areas; and, especially in the Alborz mountains, charcoal. The traditional technology used in lime burning throughout Iran is described in detail by H. E. Wulff (in bibliog., pp. 126-27). Since limestone is distributed throughout Iran, lime is nowadays burnt in almost all parts of the country, especially near large centers of population. Lime mortar is used in particular for building with fired bricks. Lime is also used in the traditional external plaster, a mixture of mud and straw (Pers. kāh-gel), in order to help preserve it.

Bibliography : H. E. Wulff, The Traditional Crafts of Persia: Their Development, Technology, and Influence on Eastern and Western Civilizations, Cambridge, Massachusetts, and London, 1966.

(E. Ehlers)

ii. Early Use of Lime Mortars

The earliest use of lime mortar in Iran is difficult to document because archeologists have not always made the distinction between lime mortar and gypsum (calcium sulfate) mortar (gač). Furthermore, both types of mortar may be tempered with a variety of organic and inorganic materials which affect their appearance as well as their setting time and adhesive qualities. Lime mortar may be divided into two main categories, hydraulic (able to set under water) and non-hydraulic, and these in turn may be further subdivided (for a summary of mortar types see Architectural Publication Society, The Dictionary of Architecture, London, 1849, IV, pp. 89-90). Roman engineers captured by the Sasanian king Šāpūr I (A.D. 242-72) apparently introduced hydraulic lime into Iran, particularly for the construction of bridges.

Non-hydraulic lime mortars appear earlier at the late Parthian (2nd-3rd cents. A.D.) sites of Qāḷʿa-ye Yazdegerd in Kurdistan (E. Keall, “Qaḷʿeh-e Yazdigird: A Question of Its Date,” Iran 15, 1977, pp. 1-2; idem, M. A. Leveque, and N. Wilson, “Qaḷʿeh-i Yazdigird: Its Architectural Decorations,” Iran 18, 1980, pp. 1-2, 8, fig. 5 ; and pl. IIIc), Qaḷʿa-ye Zaḥḥāk in Azerbaijan (W. Kleiss, “Qaḷʿeh Zohak in Azerbaidjan,” AMI 6, 1973, p. 168), and possibly at Neh in Sīstān (U. W. Hallier, “Neh—eine parthische Stadt in Ostpersien,” AMI 7, 1974, pp. 182-83 and pl. 39.3). The appearance of lime mortar at the Seleucid (3rd-2nd cent. B.C.) site of Āy Ḵānom in Afghanistan (P. Bernard, “Campagne de fouilles 1974 à Aï Khanoum (Afghanistan),” Comptes rendus de l’Academie d’Inscriptions et Belles Lettres 1974, pp. 175-80, and figs. 4-8) and its reported occurance at Seleucid Susa in Ḵūzestān (M. A. R. Colledge, Parthian Art, Ithaca, 1977, p. 28) suggest that the use of lime mortar began before the Parthian period. The discovery of slabs and bricks of a concrete-like substance in the Jemdet Nasr levels (late 4th millennium B.C.) at Uruk in southern Mesopotamia demonstrates that at least some craftsmen in a neighboring region were experimenting with a sort of lime mortar even earlier (S. Lloyd, “Building in Brick and Stone,” in C. Singer, et al. eds., A History of Technology I, Oxford, 1958, p. 462, and H. J. Lenzen, “Nachtrag zu dem Steinstiftstempel,” in “XXIII. vorläufiger Bericht über die . . . Ausgrabungen in UrukWarka, Winter, 1965,” Abhandlungen der Deutschen Orient-Gesellschaft 12, 1967, p. 35 and pl. 21 a & b).

Bibliography: Given in the text.

 

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آهک aahak    

 

(E. Ehlers, T. S. Kawami)

Originally Published: December 15, 1984

Last Updated: July 28, 2011

This article is available in print.
Vol. I, Fasc. 6, pp. 623-624

Cite this entry:

E. Ehlers, T. S. Kawami, “Ahak,” Encyclopædia Iranica, I/6, pp. 623-624; an updated version is available online at http://www.iranicaonline.org/articles/ahak-lime (accessed on 16 March 2014).