Chemistry of Fresco - Paper Example

Introduction

The term fresco refers to "fresh" in the Italian language. The major feature of the fresco is the pigment is used in a lime plaster surface that is wet. One of the oldest frescoes can be located in Greece in the 200 B.C. At the period of the Italian Renaissance during the 15th C and 16th C, there was perfection done to the fresco painting. A good example of the fresco of the era is the chapel ceiling of Sistine in Michelangelo. Fresco is normally painted on the ceilings and walls. It involves a plaster layer appliance directly to the wall to smoothen the surface of the wall. This layer is known as the arricio layer. After the layer has dried and hardened, another layer called intonaco is applied, where the pigments are applied too. Although, before the intonacco layer gets dry, the pigments must be added. This necessitates the reason for the artist to be fast in an attempt to do much of the activities as the layer dries up before the pigment is added, the artist is considered unlucky.

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The chemistry of fresco initiates with the reaction involved in the preparation of the required materials. The basic raw material is the limestone, which is gotten from the rocks containing this ore. Limestone contains the calcium carbonate (CaCO3) which is the abundant mineral found globally as a result of the easiness in accessing most of the limestone mineral containing rocks. The initial step involves the conversion of limestone to lime, which is sometimes referred to as quicklime in the laboratory. Lime, which is calcium carbonate (CaO) is prepared by heating at over 800 degrees Celsius of the calcium carbonate. In this combustion, carbon dioxide is gotten as the byproduct. The chemical reaction that describes this reaction is as written:

CaCO3(S) CaO (S) + CO2(g)

The quicklime produced is a solid white in color with a high melting point. As a result, before the invention of electricity and lighting, large chunks of lime were heated and used as a source of lighting since it glows white. The light produced was applied in illumination of theater stages which led to the source of the name 'limelight." The by-product, carbon dioxide, which is a gas gets diffused and escapes in the air. The stage that follows is called "slaking" (Topal & Fresco, 1974). It involves the addition of water to the calcium oxide so as to slake it. As a result of slaking, a product known as calcium hydroxide (Ca(OH)2) is formed. The product is also referred to as slaked lime. The reaction is exothermic, thus produces a lot of heat in the process. The equation for the reaction of the lime with water is as follows:

CaO(s) + H2O(l) Ca(OH)2 (aq) + HEAT

Lime is permitted to slake for a period of time. The time period process involved permits as calcium oxide as possible to react by ensuring more contact with water by giving it adequate time. This is because calcium oxide is not completely soluble in water. This leads to much time being taken for the water to fully interact with the calcium oxide. In contrast to the traditional method, the calcium oxide was reacted with water in large pits and was normally called "pit lime." The calcium hydroxide formed does not dissolve completely in water as it is slightly soluble. As a result, a white milky suspension is formed in water. The milky suspension of calcium hydroxide is a caustic substance since it is a strong base. There must be carefulness and precautions undertaken in dealing and handling such substance since a long period of exposure can lead to serious skin damages.

The slaked lime material is now ready for use by the artist at this point. The artist mixes the slaked lime with sand to create the real plaster that is used in the wall. Normally, coarse sand is applied for the preparation of the arricio layer whereas in preparation of intonaco sand, a layer is fine sand is used. On application of the intonaco plaster, the pigment is added. The pigment is comprised of a suspension in water, which implies that the pigment is insoluble in water. On application of the pigment to the plaster, they are absorbed by the plaster and thus become part of the intimacy other than the surface coating. After the application of the intonaco plaster, the artist should finish the painting before it dries. Normally, the artist will try to paint 3-5 square meters section in the area. Additionally, the pigments should have stability in an environment of alkalinity since the calcium hydroxide is an alkaline in nature.

The drying process of the plaster is not a chemical one but a physical process since the slaked lime does not undergo any more chemical changes. There is an evaporation process involved as the water evaporates which leaves the dry slaked lime on the wall or ceiling as applied. The fresco is made more robust through the chemical reaction that happens slowly with the loss of water. The calcium carbonate formation causes a hard and stable surface that causes the trapping of the pigments. The reaction is a slow as it takes a long period of time to occur, it may take even centuries or decades.Later the atmospheric carbon dioxide reacts with the calcium hydroxide to form calcium carbonate as shown below:

Ca(OH)2 (s) + CO2(g) CaCO3(S) + H2O(l)

There are various color types of paintings of fresco. They include chemically stable pigments of the earth such as yellow, terraverde, ochre, white, red and charcoal black. Pigments other than this discolor as they react with air, where over a period of time; lead white may turn to black whereas azurite blue turns to green. Unless acted upon by external forces that may damage it, frescoes are permanent because of their chemical composition. The main damaging force is sulfur which is capable of reducing limestone to dust (Fresco color, n.d.). Sulfur may attack frescoes by air and water pollution. In the fresco, water plays the role of a binding agent that facilitates the pigment and plaster merger, and after the painting is set by the plaster it becomes the wall's integral part.

Conclusion

Frescoes, therefore, require one to be skillful and be of enormous speed. The procedure requires artists to make prior plans, think of the section subdivided section space and have thoughts of design as a shape that is strong. This results to the new appreciation, particularly in the old renaissance Italy, of the powerful and large forms of the monuments. Currently, fresco has undergone mini-renaissance globally over the last few years, all credit to the fresco's exhibits in the museums and the many fresco schools.

References

Fresco color. (n.d.). Encyclopedic Dictionary of Polymers, 439-439. doi:10.1007/978-0-387-30160-0_5224

Topal, M. D., & Fresco, J. R. (1974). Polynucleotides. Biophysical Chemistry,2(2), 193-195. doi:10.1016/0301-4622(74)80043-8