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Chemistry 103 Lab: The Fresco Technique Introduction.  The fresco technique is one of the most ancient and widespread art forms in world. The raw materials--lime, sand, and colored clays--are geographically common, easy to collect, and process. In contrast to other painting techniques, the pigment used in frescoes is applied directly to the surface--wet plaster--without a binder.  The wet slaked lime [Ca(OH)2] plaster reacts with carbon dioxide, CO2, in the air to become insoluble calcium carbonate, CaCO3,  which  acts  as  the  binder  for  the  applied  pigment.    This consolidation  of  the  pigment  into  the  plastered  wall  itself  makes  fresco  paintings extremely durable, but, at the same time, vulnerable to any deleterious environmental conditions to which the wall is subjected.  In this lab, student will create small fresco paintings on tiles and explore the chemistry involved in fresco creation, degradation, and restoration.  This  lab  is  an  adaptation  and  expansion  of  a  similar  one  developed  by Professor Sue Roper of Sacramento City College in California for a course on chemistry and art. Terms used in fresco paintings. fresco fresh giornata one day’s work, usually 3-5 m2 (a saint’s head) arriccio underlying coat of plaster applied directly to the wall intonaco last coat of plaster applied the day of painting a secco " when dry,"  painting the dry fresco pigments in organic binders such as egg, oils, or waxes pentimenti corrections added to the painting after the day’s work sinopia stencil of the major shapes of the painting transferred to the wall before painting begins, sometimes called the cartoon Preparing a Fresco.  Preparation of the painting surfaces involves the construction of a wall  coated  with  layers  of  plaster  of  increasingly  finer  texture.    The  first  step  in  the preparation is the heating (calcination) limestone (calcium carbonate, CaCO3)  at  800- 900ßC to make porous lime (calcium oxide, CaO). HEAT     + CaCO3(s) CaO(s)     + CO2(g) (1) To form the plaster for fresco work, the lime is "slaked."  The slaking process, which requires the addition of 2 or 3 moles of water for each mole of lime, yields calcium paste or lime putty, an aqueous gel of thin crystals of calcium hydroxide. CaO(s)     + H2O(l) Ca(OH)2(s)   +   HEAT (2) Excess  water  acts  as  a  lubricant  so  that  the  crystals  slide  easily  over  one  another. Historically, lime was slaked in pits or troughs over a period of at least six months to obtain lime putty of the desired consistency.  Artisans in Michelangelo’s time use plaster aged  for  as  long  as  ten  years.  Fresco  plaster  itself  is  made  from  the  slaked  lime  and varying  portions  of  sand  or  marble  dust.    Generally,  walls  are  plastered  with  several layers of such fresco plaster in order of decreasing proportions and particle size of sand. The first layer of plaster, the arriccio (1-2 cm thick), consists of one part slaked lime to two parts of sand; some fresco techniques use several layers of arriccio. Hardening of the arriccio on the wall includes several simultaneous physical and chemical process: the