We give this denomination to colours which we can produce, and more or less fix, in certain bodies; which we can render more intense, which we can again take away and communicate to other bodies, and to which, therefore, we ascribe a certain permanency: duration is their prevailing characteristic.
In this view the chemical colours were formerly distinguished with various epithets; they were called colores proprii, corporei, materiales, veri, permanentes, fixi.
In the preceding chapter we observed how the fluctuating and transient nature of the physical colours becomes gradually fixed, thus forming the natural transition to our present subject.
Colour becomes fixed in bodies more or less permanently; superficially, or thoroughly.
All bodies are susceptible of colour; it can either be excited, rendered intense, and gradually fixed in them, or at least communicated to them.