What is the nature of colour of things and how do colorants provide colour?

All what we can see is just one part of the light falling on the objects: the reflected side.

Radiation is a way of transmission of the energy that doesn’t need of a material element to be generated. It is the energy coming from the Sun, the radio waves, the remote controls, etc.

These radiations are transmitted through electromagnetic waves and the only difference among the infrared rays of the remote controls, the FM waves, the ultraviolet rays or the visible light is the frequency or the no of oscillations per second, also called Hertz (Hz), of the aforesaid waves.

So, we have waves from just a few hundred of hertz (radio waves) to waves of about 1020 Hz; millions of billions of hertz (gamma rays) generated in the stars and in nuclear reactions.

Electromagnetic waves of all the range of waves before said come from the space. The Sun also emits waves of all the range but it does it preferably between 400 and 900 billion of Hertz. Human organism adjusted to this element in such a way that it is able to detect, through the sense of sight, this rank of preferential frequencies. Waves belonging to this rank are called light. And it is not just that, we can also distinguish between one type of frequencies and the other ones in that rank because we perceive them as different colours: from red shades of light of about 400 billion hertz to the violet shades of 900 billion hertz going through all the range: orange, yellow, green, blues, etc.

The structure of the human sight organ includes some cells called cones that are placed in the retina. There are three types of cones: those which are mainly sensitive to red colour, those mainly sensitive to green colour and the ones mainly sensitive to blue colour. That’s why these three colours are called “primary colours of light”. The mixture of lights of colours is known as additive mixture. Mixing those colours two by two we get secondary colours. The result of mixing these three colours is white light.

Diagram 1: additive mixture

An important detail to be taken into account is that each colour can be obtained either by waves of the exact frequency corresponding to that colour (monochromatic light), or by mixing waves of different frequencies that can produce the same effect in the receptor cells, and in short, in the brain.

Thus, primary red can be obtained from light with a frequency of 4,3 . 1014 Hz or with a waves additive mixture, for example, between 4 . 1014 and 5 . 1014 Hz, that can produce the same effect in our organism. Most of the colours we can see are additive mixtures.

The binary mixture of primary light colours produces:

Red + green = yellow

Red + blue = magenta

Green + blue = cyan

Natural light (sun light) is a particular case of white light. When we let natural light go into a room all the objects are exposed to the same type of light, however each object reflects just a part of the light it receives and, besides, it reflects it with preference for some frequencies, that’s to say, there are frequencies that are reflected and others that aren’t. The non-reflected frequencies are absorbed by the atoms and molecules of the objects in a way that they gain vibration energy, that’s why the objects heat up when lighted.

Then, what happens when there are frequencies of that “white” mixture that are not reflected? Well, the objects don’t reflect the white light any more. They reflect “light with colour” and, as each thing reflects a different colour, we are able to distinguish ones from the others, their outlines and their shapes, which is quite practical.

Colorants are a bit complex molecules able to absorb light in the visible frequencies. The light reflected by the colourful objects is the additive mixture of the non absorbed colours. It is said that the colorant absorbs certain frequencies of the light it receives.

For example, if a colourful object receives white light (mixture of red, green and blue: See Diagram_1) and the colorant absorbs the blue part, what is reflected will be red and green: yellow. We’ll have then a yellow colorant.

If a colorant absorbs blue and green, it will reflect red; we’ll have then a red colorant. If a colorant absorbs red, green and blue, it will reflect almost nothing; we’ll have a black colorant. (See diagram_2)

Diagram 2. Absorption of colour

The colours obtained with colorants (by subtraction or absorption of part of the light) are called pigment colours. The colorants that absorb a primary light colour produce what is known as “primary pigment colour”. There are three:

  1. Yellow: it just absorbs blue (it produces an additive mixture of red and green)

  2. Magenta: it just absorbs green (it produces an additive mixture of red and blue)

  3. Cyan: it just absorbs red (it just produces an additive mixture of green and blue)

We can mix colorants to obtain new colours. The yellow one is a colorant that absorbs blue and the cyan one is a colorant that absorbs red. The mixture generates a substance that absorbs blue and red: a green colorant.

The mixture of primary pigment colours produces primary light colours, as we can see in the Diagram-3.

Diagrame 3: substractive mixture

Observe that mixing yellow and magenta it is subtracted blue and green respectively, obtaining a red colorant; mixing magenta and cyan you can subtract green and red getting blue.

Mixing yellow, magenta and cyan it is subtracted blue, green and red, that’s to say, it absorbs in all the visible rank and produces black (in fact, different grey colours are obtained).

An interactive website is available; in it additive mixtures can be made ( the box in the top of the page where you can read “Light mixtures”) and subtractive mixtures (the box in the bottom of the page where it reads “Paint mixtures”). The intensity of each one of the primary is regulated among values from 0 to 255. It also allows to adjust the percentage of each colour in the mixture.(link in the web)

Therefore, every time we add a colorant to a mixture we are subtracting more colours to light. This is the reason why the mixture of colorants is called subtractive mixture. In short time we’ll publish an article with a practical example of a mixture of dyes applied to polyester fabric.

Salvador J.Ros Turégano

Translated from Spanish into English by Edu Grao and Alicia Hergueta


Tuesday the 19th. Joomla Template Creator. Fashion Laboratory
Copyright 2012
Licencia de Creative Commons mec
All works by Laboratorio de moda is licensed under a Creative Commons Reconocimiento-NoComercial-SinObraDerivada 3.0 Unported License.

Calcular Page Rank