Colloidal particles of Ca(OH)2:: Properties and applications to restoration of frescoes

We studied the synthesis and characterization of Ca(OH)(2) colloidal particles and their application to the restoration of wall paintings. Submicrometer Ca(OH)(2) crystalline particles have been obtained by mixing equal volumes of NaOH and CaCl2 aqueous solutions with different degrees of supersaturation (from 2 to 10) and in the temperature range 60-90 degreesC. The Ca(OH)(2) particles are crystalline and have the appearance of hexagonal platelets with thicknesses of a few nanometers, as determined by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and atomic force microscopy techniques. The kinetic stability of dispersions of Ca(OH)(2) particles in water and propan-1-ol has also been studied in view of their possible application in wall painting conservation. A successful example of this application to the restoration of Santi di Tito's wall paintings (16th century) in the Santa Maria del Fiore Cathedral in Florence is also reported.