Page 64 - DILMUN 14

Gypsu١ is a hcihydrate of Calcium Salphate (CasO,) obtaincd by heating at about
I30vC n:atura١ gypsun١ mineral (CaSO‫ﻱ‬. H,O). Ground to powdcr and mixed with water,
the burnt gyps١ rchydrates a١d sets rapidly in a solid forn. If the hydrate is heated
above ١70'C, ١١ the watcr is driven off and a١ hydrous Calcium Sulphate is formed
(CaSO,), which rcacts very slowly with water. Lime, instead, is obtained by heating
lincstonc that is cssentially composed of Calciunm Carbonate. At a temperature of
900- I000vC, calcination takes place and the Calciun Carbonate (CaCO,) is trasformed
in Calcium Oxide, or quick linc (CaO,). When soaked in water, the lumps of quick lime
rcact harshly forniing a white paste, the lime putty or slaked lime (Calcium Hydroxide:
Ca(OH),). Eposed to the air, the Calcium lydroide combines very slowly with the
atmospheric Carbon Dioxide (CO,) and sets hard in its previous form of Calcium
Carbonate.

wo samples have been taken from the North wall of the sassanid fortress at Oal'at al
Bahrain. One has been microscopically cxamined (McMillan), thc other chemically
analysed (Longuet).

Actually, one sample of very hard mortar taken from the rampart of the Hellenistic city
at Oal'at al Bahrain appears at microscopic examination (Mc Millan) to be "mainly
composed of carbonate matri‫ﻡ‬.

Longuet.

Me. Millan, Longuet.

٠As for the different phases of Bahrain fort, see M. Kervran et al: "Bahrain at the XVI
century, an impregnable island", 1988, Ministry of Information Press.

vo samples have been taken, one from the North enceinte, the other rfom the wall of
the basse cour. Both have been visually examined, the first one has also been chemically
analysed (Mc Millan).

Actually, it would be incorrect to dismiss the possibility that clay and not necessarily
sea clay was used raw. Accordingly to Wulf٤ (he traditional crafts of Persia, MI Press
I966, p 108) "a lime-mud-stone mixture becomes as hard as rock'.

Mc Millan.

According to the visual estimate, the amount of lime seems to range between 10% and
30%.

Wultf, he. traditional cratfs of Persia, p. 113.

More precisely: after 1609 and before 1635 (Kervran).

AI١ the samples have been taken rfom the East bastion during the restoration directed
by Dr. Walls.

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