From what we have said, it will be seen that the relations and harmony of colours form a complex subject, requiring constant and careful study; one, indeed, into which he who would become a colourist must enter heart and soul. For as colouring is the beginning and end of a painter's craft, so colour in all its aspects must be the chief lesson of his life. And this lesson can only be learnt, by ever watching with a loving eye those wondrous colourings of nature, in which there is nothing inharmonious or out of place. PART II. * * * * * ON COLOURS AND PIGMENTS GENERALLY. CHAPTER III. ON CLASSES OF COLOURS. By mixing his _colours with white_, the artist obtains his _tints_. By mixing _colours with colours_, he produces compound colours, or _hues_. And by mixing _colours or tints with black_, he gets _shades_. It is a common error to confound these distinctions. The above classification of colours enables us to understand the simplicity of relation which exists among an infinity of tints, hues, and shades of colour. Also, it is calculated to give precision to language respecting colours, the nomenclature of which has too often been vague and uncertain. There are five classes of colours, viz.:--the _Neutral_, the _Primary_, the _Secondary_, the _Tertiary_, and the _Semi-neutral_. _Neutral Colours_ are three only, _white_, _black_, and grey. According to the laws of Optics, the two first comprise all other colours synthetically, and afford them all by analysis. These are sometimes called "extreme" colours, grey being their intermediate. _Primary Colours_ are three only, _yellow_, _red_, and _blue_. They are such as yield others by being compounded, but are not themselves capable of being produced by composition of other colours. By way of distinction, they are occasionally designated "entire" colours. _Secondary Colours_, are three only, _orange_, _green_, and _purple_. Each of these is composed of, or can be resolved into, two primaries. Thus, orange is composed of red and yellow; green, of yellow and blue; and purple, of blue and red. _Tertiary Colours_ are three only, _citrine_, _russet_, and _olive_. Each of these is composed of, or can be resolved into, either two secondary colours, or the three primaries. Thus, citrine consists of green and orange, or of a predominant yellow with blue and red; russet is compounded of orange and purple, or of a predominant red with blue and yellow; and olive is composed of purple and green, or of a predominant blue with yellow and red.