A unique phenomenon in the history of Central Asian architecture are ancient architectural monuments of Uzbekistan — an important source of learning about the art and material and spiritual culture of the Uzbek people. These monuments have some specific features that reflect the achievements and the triumph of architectural thought of the time when they were created.

Scholars and tourists from all over the world come to our country to explore and admire the work of the great architects of Uzbekistan, which are a vivid example of innovation and progressive trends in architecture.

But however optimal may be the conditions for protecting the ancient buildings, they still require special attention and regular maintenance and restoration. From the years of independence in many cities across the republic there have operated companies and workshops producing construction and finishing materials, with continuous research and development effort. High professionalism and experience of traditional master-craftsmen enable learning the secrets of old masters. Quire relevant is the issue that concerns the degree of scientific approach, restoration quality, and the effectiveness of the work performed. Every historical monument requires restoration that takes into account the choice of construction and finishing materials used by the masters originally. Before the restoration can start, it is necessary to identify chemical composition, recipes, roasting method, type of raw materials used, and the colour palette of the period in question. Painstaking study performed by scientists of the originals details used in construction makes it possible to get a clear an accurate picture of the restoration process.

In this domain Uzbekistan has accumulated a wealth of scientific experience through the studies of architectural monuments, the chemical composition of building materials, mortars, finishing materials, physical and chemical properties (hardness, density and water resistance, as well as resistance to salt, moisture and low temperatures). As a result, many architectural monuments regained their original look and grandeur. Nevertheless, one can argue that in terms of restoration not all scientific and practical issues have been positively resolved. Results obtained in a single scientific and practical research centre cannot apply to the monuments of the entire region. Therefore, when using academic research, manuscripts and ethnographic data, it is essential that one made adjustments and clarifications with regard to a particular object.

Scientific data confirm the use of certain traditional building materials and mortars that had gone through a long evolutionary process. Statements made by some authors that the construction of architectural monuments was the work of visiting masters can be considered unjustified. From the Bronze Age local masters made jewellery, beads, and from the 12th century in the potters’ quarter in Samarqand they produced richly painted glazed crockery known as «lustraviy». In the 13th-14th centuries, residents of Khorezm used glazed pottery with rich mosaic. According to Professor M. Kadyrniyazov, the proportion of archaeological ceramic finds in the Shemakha fortress was 49.03 and 43 percent in Mizdahkand. During the reign of the Temurids, mosaic began to be extensively used in architectural monuments.

To manufacture ceramic bases, masters used local clay, and to produce mosaics they added liquorice plant ash to powdered quartzite and silica sand. Local architects exercised a very creative approach to their business, making good use of the centuries-old experience. Sometimes they could find a solution using only the resources that were at hand — local raw materials, mineral dyes and plants. For instance, the branches, roots and leaves of liquorice plants have different content of sodium and calcium oxides in different seasons, therefore, these plants were gathered taking this fact into account. The masters knew that the ash content is not homogenous and that not all chemical compounds present in the ash react similarly to the silica sand.

Having thoroughly studied Beruni’s book «Mineralogy» written in 1048, they concluded that the charge (the mix of raw materials) should be molten for a few days in a clay pot — crucible. As a result of heating, most oxides fused, forming the glass, and minerals that did not react, surfaced as scum. After removing the scum, in the process of melting, a clean and clear liquid turned into a high-quality glass. Later on this method was improved by installing a shelf in a kiln, on which the silica sand with plant ash were placed. After several hours of heating, the charge melted and trickled down. The substance was collected, let to harden and then ground on the grindstone to be used for glazing. This process was called «frittalanish» and was considered more practical and less labour intensive.

The high art of the ancient masters is vividly reflected in the structures they built. In the 11th-17th cc. architectural monuments they employed glazes tiles, the chemical composition of which was classified into 17 groups; in six of them the main component was alkaline silica, and in the other eleven — alkali-aluminium-tin, the oxide silica glaze. To obtain the composition of the first group, they added crushed quartz or its white sand with liquorice plant ash to the charge with mineral pigments; and for the second — they added aluminium and tin oxides to the same mixture. The differences between these two compositions in their finished form were as follows: the first one produced clear, transparent glaze, whereas the second one was a dark glaze that blocked sun rays. A special additional layer, engobe, provided good cohesion of ceramics, tiles and glaze, as well as helped to achieve the brightness and contrast of the design. A coat was prepared using ground white sand, white and other types of clay. The mosaic longevity depended on the coat quality. The design was created on the engobe surface, which was covered with glaze, or on the mosaic.

The aforementioned first group glaze was introduced into architecture from the arsenal of local glassblowers. The elements of traditions were preserved in mineral pigments of coloured glaze. On the territory of the Bronze Age Central Asian, with the development of metallurgy, non-ferrous metals waste accumulated in the vicinity of historical sites. Most of this waste material was colouring copper compounds, which were widely used by the population, and later on — by glass blowers and architects. Already in the antiquity, and especially in the Middle Ages, pigment types diversified with the introduction of cobalt, antimony, tin and aluminium oxides.

The application of advanced technology is very important for prolonging the life of objects under restoration. Following a recommendation of Mirumar Asadov, the renowned master of architectural restoration and the Hero of Uzbekistan, one innovation invented at the Institute of Archaeology of the Academy of Sciences was tested in September 1986 on two small mosques located in the courtyard of the Bibihanum mosque in Samarqand. A rapidly wearing part of a blue dome of one the mosques that were restored at the same time (near the Siyab market) was sprayed with a solution of di-iocyan xylol monomer with added catalyst — triethylamine. Later on it was discovered that the exposure to air and sunlight made monomers turn into polymers that created a thin, transparent film on the dome surface. Chemical treatment filled the cracks and indentations on the dome, thus preventing leakage during rain. Now the surface of the dome was safe from weeds, snow and rain. For six years after the treatment no vegetation grew on the dome, and the glaze was not damaged; only in the 7th year damage to the surface began. Meanwhile, in the dome of the other mosque, which was also restored but not treated with the chemical, the process of disintegration began already next year.

Experience shows that achievements in chemical industry and science open great prospects for further scientific discoveries.

Abdugani Abdurazzakov