The matter of values enters into the essential quality of every work of art, and especially of a portrait. It is the truth of their rendering that will give a faithful likeness. By the term values is meant the relations of light and shade to each other. This subject has been so admirably treated by John Burnet in his essay entitled "Practical Hints on Light and Shade,"[C] that I give his observations on this point.

"Before proceeding to investigate light and shade in their various intricate relations, it may be proper to notice a few of the more palpable and self-evident combinations; and for the better comprehending of which I shall divide them into five parts, viz.: Light, half-light, middle tint, half-dark and dark. When a picture is chiefly composed of light and half-light, the darks will have more force and point, but without the help of strong color to give it solidity it will be apt to look feeble, and when a picture is composed mainly of dark and half-dark the lights will be more brilliant; but they will be apt to look spotty for want of half-light to spread and connect them, and the piece be in danger of becoming black and heavy. And when a picture is composed chiefly of middle tint, the dark and light portions have a more equal chance of coming into notice, but the general effect is in danger of becoming common and insipid. Light and shade are capable of producing many results, but the three principal are relief, harmony and breadth. By the first the artist is enabled to give his work the distinctness and solidity of nature; the second is the result of a union and cement of one part with another; and the third, a general breadth, is the necessary attendant on extent and magnitude. A judicious management of these three properties is to be found in the best pictures of the Italian, Venetian and Flemish Schools, and ought to employ the most attentive examination of the student, for by giving too much relief he will produce a dry hard effect, by too much softness and blending of the parts, wooliness and insipidity, and in a desire to produce breadth of effect he may produce flatness."

The student should make a careful study of the values, as upon these will depend the entire effect of the portrait and its fidelity as a likeness; and the absence of these qualities of rendering light and shade are one of the marked features of the work of amateurs, as they are apt to make their shadows too dark and their lights too light. You should compare the portrait with the photograph you are working from, and preserve the same contrasts between the lights and shadows in order to produce satisfactory results. The best way of examining your work is by the use of a mirror. To the student the mirror is his best critic. It is before this silent observer that he submits his work with the certainty of receiving an honest criticism. At every step of your progress look at your work in a good mirror, as here it is changed about, the left side being the right side, and no error will escape detection. Sometimes you will see that what appeared true was in reality false, what seemed graceful in contour was distorted; here an eye which you thought was looking at you quite straight now mocks you from the glass in manifest obliquity; the mouth, which you thought had a pleasant expression, now looks as disdainful as can be. And so all through your work you will be startled; you will doubt the mirror. Doubt it not; your work is false. If you will be convinced show it to some competent artist, and he will confirm the judgment of the impartial mirror. Experience will soon teach you to put such reliance on its never capricious council that you will follow its suggestions implicitly, and, when your work is altered, the result will satisfy you invariably, that, as the proverb says of two heads, so two images are better than one. When you have come to this conclusion there is not a beauty of eighteen who will consult her glass (though it is true for a somewhat lighter purpose,) more eagerly, more devoutly, more frequently, or finally, we hope, with more triumphant satisfaction than will you.