OIL OF VITRIOL OISE. 



297 



posing power. A general idea of the process may 

 be formed from the following account : A quantity 

 of oil is placed in an air-tight vessel, in such a man- 

 ner that it may flow into retorts, which are kept at a 

 moderate red heat, and in such proportions as may 

 regulate the production of gas to a convenient rate ; 

 and provision is made that this rate may be easily 

 governed at the will of the operator. The oil, in its 

 passage through the retorts, is principally decom- 

 posed, and converted into gas proper for illumination, 

 having the great advantages of being pure from sul- 

 phureous contamination, and of supporting a very 

 brilliant flame with a very small expenditure. As a 

 further precaution, to purify the gas from oil which 

 may be suspended in it in the state of vapour, it is 

 conveyed into a wash vessel, where, by bubbling 

 through water, it is further cooled, and rendered fit 

 for use. It then passes, by a proper pipe, into a 

 gasometer, from which it is suffered to branch off in 

 pipes in the usual manner. 



OIL OF VITRIOL. See Sulphuric Acid. 



OIL-PAINTING. The art of painting with oil- 

 colours, which to this day are the kind most com- 

 monly used for large pictures, has, on account of its 

 liveliness, strength, agreeableness, and natural ap- 

 pearance, on account of the variety and mixture of 

 tints,, in short, on account of the charm of the 

 colouring, pre-eminence above other kinds of paint- 

 ing. The colours are somewhat darker, but also 

 more brilliant than water-colours. Painters in oil- 

 colours have succeeded in imitating the enamel with 

 which nature adorns her productions, the softness 

 and mellowness which give the greatest charms to 

 landscape, the transparency of the shades, and the 

 blending of the colours. Oil-paintings are also but 

 little injured by exposure to water and other mois- 

 ture , for the oil-colour is not easily destroyed when 

 it is once dried, and a spot can be painted over as 

 often as the artist pleases. The frequent retouching 

 which this kind of painting allows, enables the artist 

 to produce the finest harmony, and the highest effect 

 of colours, with more ease than is possible with water- 

 colours, which must be left to stand as they were first 

 laid on. Oil-colours can also be laid on over each 

 other, so that the under one appears through an 

 important advantage, which water-colours have not. 

 Besides, as oil-colour is tenacious, and the neighbour- 

 ing tints do not run into each other, the painter can 

 obtain both a better mixture and a more suitable 

 juxtaposition of colours than in water-colours. On 

 the other hand, oil-paintings have the disadvantage 

 of dazzling by the glittering of the light falling upon 

 them : for this reason, an oil-painting cannot be seen 

 equally well from all points of view ; and the dust 

 adheres to it more closely, which evil will be often 

 prevented by a coat of varnish. In the course of 

 time the colours gradually become darker ; the flesh 

 tints, particularly, take a reddish yellow colour, by 

 which the truth of the picture is very much injured. 

 The fault is in the oil with which the colours are 

 made ; for all kinds of oil become yellow in time. 

 Nut oil is most commonly made use of, with which 

 the colours are dissolved and ground, and which is 

 drying in its nature. The linseed oil, as it is gross- 

 est and fattest, is used for the groundwork. Oil of 

 poppy is also substituted for nut oil. It is whiter, 

 clearer, and lighter : but, as some colours, when they 

 are ground, dry with much difficulty, various kinds of 

 varnish are used to mix with such colours. A great 

 advantage of oil-painting is that the painter can judge 

 with more certainty of the effect of his work, since 

 the colours do not change in drying, as water-colours 

 do : only, in order to prevent the colours growing 

 too dark, he must, at the beginning, make the tone 

 somewhat strong and brilliant, and preserve the right 



proportion in the oil Many, therefore, mix in some 

 oil of spikenard, which makes the colours more li- 

 quid, and evaporates rapidly. The brilliancy of the 

 colours often only hurts the effect of the picture. 



Oil-paintings are made upon wood, copper, and 

 other metals ; also upon walls, thick silk ; but now 

 most commonly upon canvass, which is stretched 

 upon a frame, and done over with glue or gold for a 

 ground ; by some, also, with white water-colours. 

 When the canvass is prepared, the outlines are drawn 

 with white chalk, and then the colours are laid on. 

 The colours are ground with what is called a muller, 

 upon a porphyry stone, until they have the consist- 

 ency of a thick paste. The pallet is made use of in 

 order to have the prepared colours in a convenient 

 situation for the work, the same being mixed and ar- 

 ranged in a proper series. At first the groundwork 

 is put on, and the sketch must be made with the same 

 tints with which the picture is finished. A person of 

 the name of Picault is called the inventor of the art 

 of removing the colours of oil-paintings from wood, 

 and transferring them to canvass. In later times it 

 has been the custom to shave off the worm eaten 

 wood very nicely, as far as the under side of the pic- 

 ture, and to transfer the latter to new wood. (See 

 Fiorillo's History of the Arts of Design.) Still more 

 common is the art of painting over (or retouching) 

 oil-paintings ; and it has arrived at a high degree of 

 perfection. Yet it is almost impossible to prevent 

 the traces of this process from being seen after some 

 time. It is also customary to stretch upon new can- 

 vass oiled paintings executed on canvass, when the 

 canvass begins to decay, or become torn, and peel off. 



There has been much contention about the origin 

 and the antiquity of oil-painting. The old and gen- 

 eral opinion was, that John van Eyck (q. v.), also 

 called John of Bruges, invented this art in the four- 

 teenth century. According to a late opinion, oil- 

 painting is much older than the time ot John van 

 Eyck, and was carried on in his time in Italy. For 

 this opinion Cennini's treatise on painting is quoted. 

 Cicognara also considers it of Italian origin, and as- 

 cribes the improvement of it to the Netherlands, who 

 seem to have the more foundation for their claim to 

 the invention, because the artists there do not paint 

 in fresco generally, on account of their climate. If 

 he is correct, the Netherlands would be entitled only 

 to the credit of having perfected or restored this art, 

 which before was not so advantageously practised, 

 and, on account of numerous difficulties, had declined. 

 Some, indeed, attribute this invention to Antonello of 

 Messina, others to Col. Antonio di Fiore of Naples. 

 Fiorillo, in his History of the Arts of Design, holds 

 to the old opinion. It is certain that oil-painting was 

 interrupted a hundred years before the time of Eyck, 

 and in the fourteenth and fifteenth centuries, until 

 his time, water-colours were universally used. In- 

 deed, they continued in frequent use at least until 

 1469. John van Eyck was fond of chemistry, and 

 his acquaintance with this science gave him an oppor- 

 tunity of restoring oil-painting. He discovered a 

 varnish with which he covered his pictures in water- 

 colours, and gave them more brilliancy and strength; 

 but this varnish dried with difficulty, and when, for 

 the first time, he put one of his pictures in the sun, 

 it cracked. This induced him to make another var- 

 nish out of nut and linseed oil, which proved to be 

 better than the former. He observed that the colours 

 mingled much easier with oil than with glue-water, 

 and that decided him to follow this method. He be- 

 gan with it between 1402 and 1410, and instructed 

 also two of his countrymen in it, namely, Roger of 

 Bruges and Roger van der Weyden. Succeeding 

 painters perfected the art still more. 



OISE ; a department of France. See Department 



