A due selection and employment of colours materially is not alone sufficient, - an adequate knowledge of their reciprocal, sensible, and moral influences in painting, is essential to the production of their full effects on the eye and the mind; and, notwithstanding these effects and influences belong to the higher aims of the colourist, and are of a theoretical bearing, the subject is so connected with the primary object of the work, that it forms also a feature thereof, in subordination nevertheless to practice; - for colouring, like every other art that has its foundation in nature, refers to a whole, and cannot be rightly comprehended, nor perfectly practised, without some attention to all its parts; - hence also the physical causes, relations, and expression of colours, have been briefly investigated therein.

So much for the design of this performance, which might have been augmented with much additional matter, had the limits of the work permitted: some few things not included in the above, but in useful connexion therewith, have, however, been touched on, among which are a detail of the materials and management of vehicles and varnishes; for the particulars of which the reader is referred to a copious Index.

As to the peculiar form this attempt has taken, it is to be attributed to the request of an eminent publisher of works of art, that the author should render a subject, which might be dry to many readers, more popular than scientific: he may, nevertheless, have failed in this particular, since he is unconscious of any talent for popularity. Whether or not the author will, upon the whole, have succeeded in the accomplishment of a useful purpose, he professes his intention to have done so, and the foundation of his attempt throughout upon truth, actual observation, and experiment, - principally in the view of the artist, - partly in that of the chemist and natural philosopher, and divested, as much as might well be, of the technicalities which keep these arts asunder.

Should the artist, as he may, find herein matters of his previous knowledge and observation, he will reflect that every reader has not the skill and experience of an artist; and if he meet with things erroneous, the author courts correction and improvement; while in return he tenders his own experience to the inquirer in any way connected with the art. With respect to the application of colours in painting, recourse must be had to practice under the direction of an able master, several of whom have published valuable works of instruction in the various branches of the art* - for of this the student may be assured, that, however useful recipes may be in cookery and pharmacy, the skill of colouring is not to be acquired by any such off-hand processes; and that perfect success therein will require - what no literary work can supply - the constant and united efforts of an able hand, a good eye, and a cultivated judgment - directed in the first instance to the works of good colourists, and perfected by an assiduous application to nature and science.

* Such are Dagley's Compendium of the Theory and Practice of Painting, in which the elements of the art are treated with classical simplicity and method; Harding's Ingenious and admirable Treatise on the Use of the Black Lead Pencil, etc.; Burnett's elegant performances On Composition, Chiaroscuro, and Colouring; and various others on different departments of the art. Those who delight in these and similar inquiries may find gratification in perusing the following recent publications: - Burnet's, On the Education of the Eye; Fielding's two elegant works On the Practice of Painting; Lady Callcott's History of the Art; Hay's Laics of Harmonious Colouring; and Phillips' Theory and Practice of Painting in Water Colours.

But though the records of literature and science cannot alone produce a colourist, nor form the practical painter in other respects, they may become most important auxiliaries, - not merely by recreating his faculties, instructing his hand, and extending the sphere of his art, by endless analogies throughout the field of history and philosophy, and the vast regions of poetic fancy; but also by exciting a just enthusiasm, and stimulating his invention, while they enlarge his judgment and refine his taste; supporting at the same time that connexion with learning which gives dignity to fine art, and raises it above mere manipulation. Indeed, there never was a truly great artist who did not unite with his ability somewhat of literary talent, inclination, or acquirement; nor is there a surer mark of a low and grovelling genius than a contempt of theory or science, and an over-devotion to the mechanical and practical in art; for the connexion of art with science, theory, and practice, and of these with literature, is most intimate and indissoluble; nor is it likely the artist should paint the worse for being acquainted with the philosophy of his art. The author derives hence an excuse for having, even in this lowly performance, attempted to draw philosophy on the one hand, and poetry and harmonics on the other, into intimate connexion with colours and colouring, by a variety of natural analogies and poetical instances, and thereby aiming at associating colour with sentiment and a moral purpose.

There remains only to be remarked, that the original plan of the work has been preserved in the present edition with no other alteration than the correction and augmentation of the practical parts and the omission of the optical and chromatic experiments appended to the quarto edition, in which respects it is hoped the work may be found improved in its practical utility.