Mosaic - History

Lightweight marble - glass marble
The mosaic is a composition obtained by the use of fragments of materials (tiles) of a different nature and colour (stone, glass, shells). The tiles are made up of many types of materials, which allow different effects and each have their advantages: pebbly, glass paste (effect of transparency, colours live), square of sandstone (cutting easy and resistant to cold), glazed ceramics (great range of colors, but is a material of difficult conservation), marble (many colours, great resistance, but it is a material is very heavy), the gold and silver (insert a layer of gold or silver in a card of glass; the layer is protected and has an effect of brightness). In Byzantium, using glazes glass wall decoration. The intensity of colors is significant but this material is expensive and very fragile. The support more widespread is the concrete (sand and cement) given its low cost and its adaptability to various contexts. It is on the wall a net, then a layer of concrete at least 13 mm thick, so as to protect the mosaic from cracking.The glue used is certainly the malta: applicable on all surfaces, you can add the lime to slow down the time for the taking. Using also adhesives based on cement, which are designed on the basis of support, with various times for the taking. The use of the two types of white glue (normal and soluble in water) is also often.
Finally, the contemporary age, noted the use of silicone sticker. The mosaic parietal consists in drawing up on the crude wall the “arriccio”, then a layer of malta made of marble, lime and pozzolana. San Marco is it made use of nails, also 37 to sqm, to support the mosaic: time is understood that it is not needed and also impede the restoration. In the XII and XIV century, in Florence, use lime, powder of marble, tufa and gums. Vasari handed down a recipe composed of lime, travertine, “cocciopesto” and egg white: lime addition to egg white cement is a very tough. For the application in work the direct method is the best one: it comes executed on site, in the conditions of light in which the work will come above all seen, important for the effect of the gold. The prefabrication is possible also on panels in reinforced concrete thick 2 cm, reinforces from metallic net; the mosaic comes executed in laboratory and mounted with grappe of brass. With the indirect method, instead, the mosaic comes prepared in laboratory, with turned over weaving glue with the flour glue on sheets of paper or burlap: it is adapted for superficial flat, like pavements and coverings of swimming pools, since weaving they will turn out on the same level and they will have the same angle-shot. If the mosaic will be of great dimensions, the surface will come decomposed in smaller and manageable parts, with the perimeter that follow the decoration or however with contours in order to camouflage the joints better. The mosaic or its sections comes placed on the layer of malta or still fresh binder and then struck with an appropriate called instrument “batti”, until that the binder is not penetrated through all the interstices between weaving. To this point the ended mosaic can be removed the paper and be carried therefore to the light. At last the system of “rivoltatura”, diffused from XIX the century, is preciser of the indirect method and concurs one greater wealth of details. Within a wood cassette, of the dimensions of the final job or one of its sections, with the waterproofed bottom, one is spread miscelata clay layer to bathed pozzolana. On this trace the design and you become part weaving directly. Once completed the mosaic, is covered with gauze, eventually reinforces with hemp burlap, join with starch or flour glue. Not hardly the gauze they are dry, can run under above the mosaic, be freed it the cassette and be removed the clay accurately, cleaning up weaving. The mosaic comes therefore transferred on the wall of support, like in the event of the indirect method. The mosaics pave them, in Greece, were constructed digging the ground until to 2 m of depth; layer of cementing with pebbles and stone came thrown one in order to obtain one convex layer, therefore a lime paste, sand and ash often 15 cm, very levelled; at last the mosaic came place. This system was much stable one. The Roman used to level the surface, to compress the ground for a greater consistency, therefore to arrange a pebble layer and pozzolana and one of pozzolana and pieces of bricks, that they came compressed; a successive layer of lime, pozzolana, powder of marble and “cocciopesto“ constituted the base for the mosaic, realized on on concrete bath. In Bizantina age a layer of bricks was preferred approaches to you, covered then with pieces of bricks, gravel, lime, pozzolana, while to Venice one came jetty base of 10 cm of lime and pozzolana and an other layer of 4 cm in order to entice weaving. The use of mosaics on support is documented already in roman age: “emblèmata” draft of, mosaics realizes to you on stone slabs, wood, branch, brass or terracotta, subsequently inserted in the superficial ones to decorate, or of icone portable of bizantina ege. Musive decorations are found also on objects of furnishing, profane liturgic or, like altars, pulpits, tables. The support can be to “cassina”, that is to have a raised frame, or smooth, in the event the mosaic goes inserted on one wall or hung. The binder for mosaic can be constituted from extinguished lime and powder of bricks and marble, stirred with water and eventually oils or rendered some; oil plaster, wax, Greek bitumen and pece, stir to you between they. Sinopia or the design, have the function to define the division of the spaces and to create a guide during the execution. It comes traced on the last layer of preparation, before the true binder and, with colors red or just black in water or recording the malta fresh. The binder layer comes spread to days, in order to avoid that it dries before that all weaving have been placed. On this layer filler the definitive design by means of cardboard or I dust off myself: sometimes it is completed with background paintings is like reference for the colors to use is in order to carry to tone the malta that it will remain in sight in the interstices. In the emblèmata one it came used one technical particular: on the support it comes strained a chalk layer, on which the design is prepared. The chalk comes then removed to small sections, inside of which comes spread the binder. The chalk that remains around the removed zone will serve from control to the mosaic in fairs. The binders of the antiquity were rendered of it vegetables or bituminous, like also the chalk or mixtures of lime and “cocciopesto” or powder of marble or sand. In the 1800 age, the oil plaster, used in the Rinascimento is resumed, and comes introduced the Portland concrete. Today they exist in commerce varies types to you of hill, it putties and malte, even if some mosaicisti prefer to prepare themselves from himself traditionally, with fine lime and sand. To weave they come cut to the measure wished with the aid of “martellina” and “tagliolo”, or with one special clamp, therefore inserted in the binder for approximately 2/3 of their thickness, with the hands or the tweezers in case of reduced dimensions. The varied guideline to second of the practised pressure and the effects of light wishes to you, species in deep the gold, in which the inclination it arrives to the 45°. This procedure creates a surface irregular, characteristic of the antichi mosaics, difficultly riproducibile with the indirect method, that smooth and uniform surface introduces one.

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