The methods of _Warkworth Castle_ were practically those used by the younger Barret, Varley, Copley Fielding, Cox, and De Wint, but after about 1830 we find opaque white coming into general use, at first merely to give increased force to the high lights, but later it was mixed freely with all the transparent colours, and toned or tinted paper was used to give greater brilliance to the body-colour. John F. Lewis worked in this way, but the hardness and glitter to which it so easily conduced led to its abandonment by the later artists who set themselves to render the delicate gradations of the atmosphere. Yet one must admit that in the hands of a master technician like Turner all the unpleasant qualities so often apparent in body-colour work can be avoided, as the _Rivers of France_ drawings prove. At the present time some artists, who aim especially at force and brilliance of colour, prefer to work in tempera, but it is doubtful whether this medium can rightly be regarded as a form of water-colour painting. On the whole we may say that the technique of water-colour has changed very little during the last two centuries. The chief change has perhaps been connected with the introduction, about 1830, of moist colours put up in metal tubes, a great convenience to artists in search of bold effects without the expenditure of much time or trouble. But even this has proved a doubtful advantage, and many artists have now gone back to the use of hard cakes of colour, similar to those with which the earlier men obtained their delicate and luminous results. (4) SOME FAMOUS WATER-COLOUR PAINTERS OF THE PAST In the previous section we have deliberately refrained from saying anything about the purely artistic qualities of the works we have referred to. This is because we have been engaged in a strictly historical survey, and to the eye of history there is no difference between the works of a great artist and those of a bungler. Both are equally patent and indubitable facts. It is the business of criticism to appraise the artistic beauty of works of art. And if in our historical survey we have kept our attention fixed generally on the works of the greater men, this is more the result of accident than design. Art criticism has already sifted much of the good from the bad in the work of the past, and it is more convenient, in a general survey of this kind, to deal with what is best known and valued. But because history can thus take advantage of what art criticism has done, that is no reason why we should confuse the two processes, and it cannot be repeated too often that historical importance or interest has nothing whatever to do with artistic value.