Читать книгу Monument Future - Siegfried Siegesmund - Страница 155

The historic multi-leaf masonry has a filling of stone rubble and mortar. The external leaf was built of travertine worked stones, rubblestones and bricks. Plaster was the binder for the mortar of all building periods and masonry types. Chemical and phase analyses of Sasanian and Ilkhanid plaster samples yielded fairly pure gypsum mortars. Maximum silicon dioxide impurities, mainly as quartz, did not exceed 8.3 mass%.

The thin section of a Sasanian gypsum mortar revealed a secondray very porous structure (Figure 2). The firing products are more or less dissolved, creating pore space which is surrounded by a gypsum matrix. Brown inclusions in the leached remnants of the fired gypsum must be regarded as impurities in the raw material.

Figure 1: North wall of the west iwan in the centre, Takht-e Soleyman.

Figure 2: Sasanian mortar with very porous structure and fragment of gypsum rock (plane polarized light).

Figure 3: Ilkhanid render with porous structure. The grains in the upper part of photograph exhibit distinct reaction rims (arrows); plain polarized light.

Embedded in the gypsum matrix are low quantities of gypsum rock fragments and brownish aggregate material with a maximum grain size of about 6 mm. Both may have entered the mortar as contaminants in the furnace or on the construction site. However, an intentional admixture as aggregates cannot be ruled out. Unreacted anhydrite was not detected.As the polarized light microscopy of thin sections showed, the Ilkhanid plaster is quite different from a Sasanian mortar. It contains still a lot of unreacted firing products with a maximum grain size up to 8 mm. Occasionally distinct reaction rims around the grains are visible (Figure 3). Both in the firing products and in the mortar matrix fine clayey (ceramic) particles occur. They most probably derive from impure raw material and not from the intentional admixture of crushed bricks as pozzolanic material. Like the Sasanian plaster the 115Ilkhanid plaster contains gypsum rock fragments with a grain size up to 8 mm. It cannot be decided whether they were added as aggregate or derive from insufficiently fired raw material. Overall, the matrix fabric of the Ilkhanid plaster appears to be denser than that of the Sasanian plaster due to the abundance of unreacted components.

Figure 4: Furnace for plaster production. Cross section (left) and view into the shaft with installation of temperature measuring device (thermocouple 1).