ألوان الطيف وألوان الأصباغ .. كتاب في سبيل موسوعة علمية .. الدكتور أحمد ذكي

Spectrum colors and pigment colors

White sunlight is decomposed, as Newton did, into colors, which are the colors of the spectrum. Sun spectrum. They are rays of color, without mass or weight.

As for dyes, they are substances with colors, with which we dye things. Substances that have mass and have weight.

We say that dyes are substances with colors. This is an inaccurate expression in science. Rather, what is accurate is to say that they are materials that, if sunlight falls on them, reflect from their spectrum the color by which they are known.

There are usually two types of dyes: one type used in painting
Walls, furniture, metals, wood, and a type of dye used for fabrics and clothing.

- Wall paints:

As for the first type of pigments, it is often a simple chemical substance, such as coal soot, red iron oxide, cobalt blue oxide, yellow cadmium sulphide, or white lead sulphate, or it is a dye formed by mixing these colors with each other.

In this case, the dye is mixed with quick-drying oil
In the air, like linseed oil: if you paint it on a wall or a door, it dries quickly. It then consists of a layer of oil in which the dye has spread small colored particles, on which light falls, such as sunlight, for example, and absorbs from it the colors of the spectrum except its color, and reflects it to the eye of the beholder.
This is the first type of dye.

- Clothes dyes;

The second type of dye is the one used to dye fabrics and clothes. In the past, it was dyed with dyes extracted from plants, such as blue indigo, for example. then . Chemists were guided by the synthesis of these dyes from coal tar, to the point that what they created of them amounted to tens of thousands, of which thousands are now extracted in industry.

The first type of paint, wall paint for example, adheres to the wall. As for dyeing of this second type, dyeing of fabric, its chemical molecules are connected to the molecules of the fabric by chemical bonds. Moreover, it is like paint on a wall. Light falls on it, like sunlight, for example, and it absorbs the colors of the spectrum except its own color, and then reflects it to the eye of the beholder.

- Spectrum of dyes:

We mentioned that dyes are substances used to paint the wall and the like.
Or dyes used to dye clothes and the like.
You look at one dye and say it is red, and at another you say it is green.

It may come to mind from what we mentioned, that the dye absorbs all the colors of the spectrum of the sun that fall on it and absorbs them all, except the red in the first example, and the green in the second example.

If this comes to mind, then this is an incorrect understanding, caused by an inaccurate expression, as we did not say “all” the colors of the spectrum. We did not say that it absorbs “all of them.”

The correct answer we come from studying the famous dye known as Emerald Green. We called this dye, as we saw it, green.

But by detecting with spectrometers in the laboratory what rays are reflected, after absorbing what is absorbed from the sun’s spectrum. We find that it reflects the green spectral color strongly, but it also reflects from the rest of the sun's spectrum, from the right of the green color, and from its left, amounts, which begin to decrease until they are erased. It reflects the colors of its largest head, which is green.

Among the pigments, there are two large heads that reflect the rays of the head. Like these purple dyes, they often have one head at the red end of the spectrum, and another at the violet end of the spectrum.

- Mixing the colors of the spectrum other than mixing the colors in dyes:

The reason for this disagreement is that the colors of the spectrum are rays, so if two rays of them, of two different colors, reach the eye, it senses them gathered together, in one color. They work by addition, and nothing is lost from either of them.

As for dye, it is a substance that absorbs as much of the spectrum's rays as it absorbs
It reflects the dominant color ray, which appears to us as red or green, depending on the dye given to us.

The important thing here is that the dye is absorbed. If you mix another dye with it, the two will cooperate in absorption. What the first leaves behind and does not absorb, the second may absorb. So we may emerge from combining the two dyes with a black dye, which has absorbed all colors of light.

We mentioned that Newton collected the colors of the sun's spectrum and spread them through his triangular prism, producing white light from them again. If we combined these colors as pigments instead of rays, nothing would result except black. Because some absorb what others reflect. They work with shortages. By subtraction. One of them may subtract what the other has retained.

It is a common mistake that we hear from color printers and others. They talk to you and say that you mix the yellow color with blue and you get the green color. They mean mixing dye with dye. This suggests that green is produced by addition. In fact, it is produced by subtraction, and has nothing to do with yellow or blue, because the yellow dye and the blue dye that are mentioned together absorb all the rays of the spectrum, and the green remains untouched. They did not create the green, but rather let it reflect to the eye.

Since the science of dyes, especially those that dye fabrics, is a science that poses a great threat to the economy and industry, for this reason scientists studied dyes extensively spectroscopically, so they knew what spectrum rays the dye absorbs and what it reflects (and there is hardly a dye in dyes that is absolutely decisive in absorbing it. For colors and their opposite) and they described the results of these studies in tables that they used, if they wanted a color by itself, to mix those pigments that make up the desired color as closely as possible. They initially mixed spectra, so if they found the color they wanted, they looked to whom these spectra they mixed belonged to. . They came out with dyes that they mixed.

Of the colors that the soul feels comfortable with,
And of the colors that cause confusion and agitation,
Blue is calm and cool, and red is rebellious and fiery.