Popular Science Monthly, December 1935
100,000 Hues by Eye produced by Du Pont dyes. This amounts to more than merely recognizing the dye itself, for a single solution may produce a different hue with each different material. He becomes familiar with dyes used for coloring leather, wood, cloth, and scores of other materials. Then he has to learn to identify most of the colors produced by competing dye manufacturers.
In five or six years, the eyes of the apprentice may become so sensitive that he can work alone, comparing colors to determine whether they are up to standard. Before that time, he does more and more standardizing, as his skill grows; but always there is an experienced color man to check his results.
Queer Facts about COLOR
There are sensitive scientific instruments for measuring color stimuli, but the human eye is the best testing device for determining physiological response to color.
If, to a batch of yellow dye, one twenty-thousandth as much red as yellow is added, a trained color expert can detect it.
Color-blindness is most common among white males, about six percent being insensitive to reds or greens or both, and two percent more, partly so.
Women are rarely color-blind.
Women generally are better judges of color than men, because they pay more attention to color.
Every piece of paper sold today is dyed. Paper is made whiter by addition of dyes.
Color experts can recognize more than 300 shades of white, and nearly as many different blacks.
The most widely dye is sulphur black.
Repeal of prohibition created a demand for alcohol-proof red dyes.
"Purple" is a word never heard in a modern color laboratory. The color expert say "red-blue" or "red-violet" instead.
The best dyes in the world are made in the United States.
The skill it is possible to develop in the normal human eye is amazing. The ordinary man is able to distinguis several dozen colors and hues, all those necessary for carrying on his daily work and recreation. The chances are that his wife can recognize colors that he does not see, simply because whe has had more experience in matching thread, picking out dress goods, and otherwise working with finer hues all her life. In other words, her eyes are better trained than his.
Suppose you visit one of these color experts while he is at work. You may find him in a laboratory where a dozen or so workers are engaged in cooking skeins of rayon yard in dye baths, rinsing them, and otherwise treating them to produce the color desired. Perhaps a manufacturer has ordered some black dye, and he wants it to match a standard he has for reference. It is necessary to test the lot of dye carefully before shipping it to the customer, to make sure that it will produce a color exactrly like the standard of sample.
And so a black dye test is being run. There, on a table in front of a north window, are a dozen skeins of black yarn - all of the same kind of black to your eyes. But the color expert, whose eyes have received years of training in recognizing colors, walks over to the table. He picks up several skeins, and holds them side by side in his hands. Rapidly he sorts them, placing them in several groups.
"This black has too much red in it," he tells you, as he lays a skein on the table. "Here are a couple on the dull side, and here are some that are too green."
And so he continues to compare and sort blacks that all look alike to you, until he finds a specimen that matches the color of the standard which the laboratory has for reference.
Artificial light is not very popular in the color laboratory. All judging of color is done by daylight, preferably that coming through a north window. The color expert will work until the daylight becomes too dim to permit accurate results, before he will turn on the electric lamps. Special bulbs and filters producing light of daylight quality are employed when artificial illumination is necessary.
There are three ways in which a color may vary from standard, and it is on this basis that the important job of color matching is carried out. First, the color may be stronger or weaker than the standard. It may still be the same color in other respects, but may be present in too low or too high a concentration. Variation in strength of the dye solution may remedy this. Second, the hue may lie on one side or the other of the standard. That is, a certain red may be too yellow or too blue; or a certain yellow may be too green or too red. Third, the color may be too dull or too bright. Brightness of a color has nothing to do with its stregth, although the untrained eye might have difficulty differentiating the two properties.
If you hand a color expert a piece of dyed cloth and ask him if it is the same color as a sample he saw yesterday, he will hand it back to you and refuse to give his opinion. For it is impossible to judge a color accurately, with rare exceptions, except by actual comparison with another color sample.
Behind the necktie or dress you are wearing may be thousands of dollars worth of dye testing, to make sure that the colors will not do a quick-change or disappearing act under conditions they are likely to encounter. After the color expert's eyes have found a certain dye sample satisfactory as far as hue is concerned, the dye has to go through a long series of fastness tests, which reveal whether or not it will retain its color in the face of severe treatment.
The dye is applied to different fabric samples in various ways. Perhaps the color would be affected by using a copper kettle for dyeing. This must be determined by actual test. Maybe it will fade when the cloth is wet with perspiration. It is therefore tested by being subjected to synthetic sweat. Several washing methods are tried, with water of various temperature. The effect of bleaches such as those used by laundries is determined. The samples are ironed at different temperatures.
In short, the dye is tested in every conceivable way, to determine just how it will behave. The results of a series of tests are combined into a novel record, which consists of a strip of cloth on which all the test pieces are sewed, together with necessary information. Some of these test reports reach a length of fifteen feet.
Many important dyes formerly were imported from other countries; but today the quality of dyes made in this country is as high as that of any foreign product, and usually higher, Dr. Rose points out. Something like three percent of the dye material is used in the United States is imported, and most of this is of the nature of specialties, protected by patents.
Frequently, the introduction of a new product depends on the availability of dyes for coloring it. Chemists have produced many new and promising plastic materials which are being kept off the market because succesful dyes and methods for coloring them have not been perfected. Dye chemists are at work, and the new materials will appear in due time; for it is seldom that the modern color wizard must admit defeat.
Sometimes, however, the dye expert must say, "It can't be done." Dr. Rose receives numerous requests for compounds that will "dye something light." This is an impossibility, because the addition of any dye always darkens the material; that is, it always makes the material absorb more light than it did before. The only way to make anything lighter is to bleach it or otherwise remove the color.
In the matter of paper, the dye chemist seems to violate this rule. Did you know that every piece of paper produced, even the white, is dyed? Natural cellulose or wood pulp from which paper is made has a yellowish hue, possibly with some other color present. To render the paper more white in appearance, a dye of a complementary color is used. That is, a color is used that, when combined with the color already present, will produce white. Thus, a yellowish paper is treated with blue dye to make it white, just as the laundress adds blueing to the rinse water to make yellowish clothes whiter.
Although this dyeing of paper makes it whiter, it actually makes it less bright. To the ordinary eye, however, the increased whiteness more than makes up for the slight loss of brightness. Tests with a photo-electric cell can reveal startling facts about paper samples. Thus, of two samples, one may be whiter than the other to the human eye, but actually less bright to the electric eye. Sometimes, the quantity of dye used for tinting paper is very small. In one instance, three sixteenths of an ounce of blue and one sixty-fourth of an ounce of red dye was used for every 1,000 pounds of dry wood pulp.
Dyes are put to so many uses that the Du Pont laboratoy must carry on research in many directions. In the laboratory are found machines for printing designs on cloth with sample dyed; equipment for duplicating, on a small scale, the dyeing process used in making leather goods; miniature paper-making plants, and various pieces of equopment for aging or developing colors.
One thing that catches the eye of the visitori to a modern dye laboratory or plant using certain kinds of dyes in that the dye solution may be colorless, while the finished material may have a most brilliant hue; or dye of one color may produce a color entirely different when applied to a material. The so-called vat and insoluble azo colors are peculiar in this respect. In the vat process, the dye, which may be of one color in solution, is changed chemically after it is in the cloth, to produce the desired color. In naphthol dyeing with insoluble azo colors, colorless materials are combined to form colored dye molecules which are firmly embedded in the fibers of the colth. Colors are aged or developed with steam, acetic acid, and other treatments.
Aside from their widespread use for coloring cloth and paper, and making printing inks, dyes find numerous other interesting applications. For tracing underground rivers, finding sewer leaks, and checking the flow of other underground waters, fluorescein, a well-known dye that gives off a greenish-yellow glow when acted upon by light, is used. The average person can detect one part of fluorescein in 100,000,000 parts of water.
Modern photography would be handicapped seriously without certain dyes used for making films and plates sensitive to green, yellow and red light. Embalming fluid, largely composed of formaldehyde, is colored so that embalmed bodies will look pink and therefore more lifelike. The Unites States Department of agriculture requires that certain imported seeds be dyed so that farmers can identify them. One method commonly used for dyeing seed is to mix it with the dye solution in an ordinary concrete mixer. In garages and machine shops, a paste containing a dye commonly known as "bearing blue" is used to test the trueness of bearings and other surfaces that slide over each other.
Not long ago, Dr. Rose received a request for dyes that would withstand the weather when applied to the feathers of living chickens. The chikens were to be marked so that they could be identified during certain scientific experiments.
Among the most unusual uses for dyes is the production of artificial clouds. In England, such clouds of carious colors are used in connection with the projection of aerial advertisements by means of giant magic lanterns.
The jackets around hot dogs are colored with a harmless dye to make them look more appetizing. Pecans and walnuts commonly are given a more attractive color by dyeing their shells.
In fact, if dyes were removed suddenly from modern industry, the world would be much more drab and dreary than it is. And if nature, ages ago, had not built a marvelous color-sensitive mechanism into the human eye, science might still be trying to find a convenient and reliable way of marching colors.