Here comes into the account the important operation of employing mordants, which may be considered as the intermediate agents between the colour and the recipient substance; various works on dyeing speak of this circumstantially. Suffice it to have alluded to processes by means of which the colour retains a permanency only to be destroyed with the substance, and which may even increase in brightness and beauty by use. XLIV. INTERMIXTURE, REAL. 551. Every intermixture pre-supposes a specific state of colour; and thus when we speak of intermixture, we here understand it in an atomic sense. We must first have before us certain bodies arrested at any given point of the colorific circle, before we can produce gradations by their union. 552. Yellow, blue, and red, may be assumed as pure elementary colours, already existing; from these, violet, orange, and green, are the simplest combined results. 553. Some persons have taken much pains to define these intermixtures more accurately, by relations of number, measure, and weight, but nothing very profitable has been thus accomplished. 554. Painting consists, strictly speaking, in the intermixture of such specific colouring bodies and their infinite possible combinations--combinations which can only be appreciated by the nicest, most practised eye, and only accomplished under its influence. 555. The intimate combination of these ingredients is effected, in the first instance, through the most perfect comminution of the material by means of grinding, washing, &c., as well as by vehicles or liquid mediums which hold together the pulverized substance, and combine organically, as it were, the unorganic; such are the oils, resins, &c.--Note V. 556. If all the colours are mixed together they retain their general character as σκιερόν, and as they are no longer seen next each other, no completeness, no harmony, is experienced; the result is grey, which, like apparent colour, always appears somewhat darker than white, and somewhat lighter than black. 557. This grey may be produced in various ways. By mixing yellow and blue to an emerald green, and then adding pure red, till all three neutralize each other; or, by placing the primitive and intermediate colours next each other in a certain proportion, and afterwards mixing them. 558. That all the colours mixed together produce white, is an absurdity which people have credulously been accustomed to repeat for a century, in opposition to the evidence of their senses. 559. Colours when mixed together retain their original darkness. The darker the colours, the darker will be the grey resulting from their union, till at last this grey approaches black. The lighter the colours the lighter will be the grey, which at last approaches white. XLV. INTERMIXTURE, APPARENT. 560.