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camplc, it is cxtrcmcly difficult to distinguish bctwccn a calcarcous sand and the
carbonatcd line sincc thicy will be both digested in acid, presenting, thercfore, a1
cquivocal aggregatclbinder ratio.

Morcover, may factors which do affcct the final perfornancc of mortars, like
the rate of drying out or thc mcthod of miing, canot be revcalcd by chemical
analysis. his being said, it is also true that what thc chemist is able to sec in a
mortar sample offcrs an important framc for both thc archacologisl and the
architcct.

E٨RLY PERIODS
Gypsum, which is often clained 1o enter into the composition of the plasters

employed in thc island until few decades ago, has been used as a binder since
renote tinmes.

A plaster sample taken fronm a burial grave of the II millennium B.C. (Hamad
own, B.S. W1; D.S. grave 2) appears, at microscopic eanination, 'to contain
very fine grained carbonate sand (٠٠٠) with silica grains set in gypsum matri+.

his does not necessarily mean that lime was not used at all; however, considering
that the preparation of gypsun required a much lower temperature than lime, it
seems more likely that gypsun was used as an earlier choice.

According to the sanples examined ٩, the use of gypsum seems to continue over
the Sassanid period 2; chemical analysis " however, has also revealed the presence
of carbonated iime, the original mi of the Sassanid mortar being possibly
composed of 30% gypsum, 20% Iime, 50% aggregates.

A similar mortar, but even richer in gypsum, has been found in vestiges of the
XIII century round tower situated on the seashore, west of the Sassanid fortress of
Oal'at al Bahrain 2.

Undoubtedly, we are facing a group of mortars based on a gypsumllime blend:
but were gypsum and lime mied together on purpose?

As mentioned above, it is very difficult to tell by chemical analysis alone whether
one of the two materials served as an inert charge, or they both acted as binders;
consequently, the hypothesis that the mi‫ﻡ‬ture was not man-made, but it was rather
in this form in the natural state, cannot be dismissed, If so, two possibilities may be
considered: either the raw mineral was heated to a temperature suitable for
gypsum, in which case the limestone would not be calcinated; or the temperature
necessary to obtain lime was reached, with inevitable overburning of gypsum which
would never rehydrate. Whether or not these mortars were artifically gauged, their

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