On Encauflic Painting. zy 



gen, into the ftate of a more or lefs dark refin ; lofes gra- 

 dually its effential hvdrogen, which makes a new combina- 

 tion, and afterwards the oxygen itfelf which has attracted, 

 the carbon; and at length leaves behind a thin layer of ac- 

 tual carbon, which in the end becomes black in the courfe. 

 of time, and confiderably qbfeures the oil-painting. By a 

 continuance of the before-mentioned flow combuftion the 

 carbon itfelf, as it were, burns alfo : if it be ftrongly acted 

 upon by the light, it attracts the oxygen of the atmofphere, 

 and again brings forward the carbonic acid or fixed air, which 

 gradually flics off. By this, which I may call the fecond 

 degree of combuftion, the painting muft become dufty and 

 friable, like crayon painting (il pajhllo) ; a phenomenon 

 which may be clearly perceived on oil-paintings, which are 

 generally covered with wood and iron-work, that they may 

 the better withftand the atmofphere. 



The afhes, oxydes, or calces of metals, which are often 

 ufed as paints, are nothing elfe than metals actually brought 

 to a burnt or faline ftate by different dofes of oxygen. When 

 the oil, during the time of the before-mentioned combuftion, 

 deprives them of fome part of their oxygen by means of its 

 well-known affinity, the metal again proportionably afTumes 

 . its natural ftate and colour ; and as the calces or aflies of 

 the iron, and particularly white lead, return to their former 

 metallic character, they become, in various ways, black, 

 by the lofs of the oxygen, which, as is well known, is drawn 

 from them merely by the contact of the light, efpecially 

 when ftrong. 



It appears' from the preceding theoretical obfervations, that 

 one can hope only for a tranfient or deceitful effect from the 

 jefrefhing of oil-paintings with oil, becaufe the harmony of- 

 the tones, which the painter eftabiifhes as fuitcd for the mo-, 

 ment, docs not proceed with equal fteps, and cannot prelerve 

 itfelf in the like meafure for the courfe of a few years, as each, 

 tint, as they fay, ought to increafe, or, to fpeak more properly, 

 to butn in proportion to it? antiquity. }t thence follows, that 



