Richardson: Color Magic With Black Light

Popular Mechanics, kesäkuu 1945

By Judith Richardson

What black light is Shortwave or ultraviolet radiations are popularly called black light. Most powerful white lights produce invisible black light when white rays are screened out with a filter
What is does
Black light is associated with the effect known as fluorescence. Fluorescence is the property possessed by over 3,000 materials of glowing or changing color when exposed to black light rays.
Bradley Smith Photo

Whether it's for fun or profit, you're sure to get a thrill out of black light, the latest brainchild of lighting science; a magic invisible ray that transforms "ugly ducklings" into colorful beauties.

Black light consists of a wide band of radiations immediately below the visible spectrum. If you filter out the white light from sunlight or any other strong white light, the remaining black-light rays then will be able to demonstrate their magic. What it is and what it does is indicated in Fig. 1. This magic is called fluorescence, and, simply put, meand that various materials change color or glow when exposed to black-light rays. Over 3,000 materials are fluorescent, and the strongest of these materials are incorporated in paints, silks, cosmetics, plastics, coated paper, smoke powders and other products. Popular light sources to activate these materials are shown in Fig. 2. Lamps for this purpose are available in several styles from 50 cents up. Fig.3 shows the disassembly of the 100-watt mercuryvapor lamp, which is most popular of the various black lights. Fig. 8 gives data which will enable you to pick a light for your purpose.

Black lights can be obtained in several popular styles in a price range from fifty cents up. Photo at right shows dissembly of popular 100-watt mercury-vapor flood. Charasteristics of all lights are given in handy tabular form in Fig. 8

How do you use this black light? Well, if you want it just as a hobby or for decoration, look at the little whatnot cabinet shown in Fig. 4. [PUUTTUU] Nice enough under white light, but under black light the display on the lower shelf is truly a magic fairyland of color. Fig.5 [PUUTTUU] is the poor reproduction in black-and-white, but it will give you an idea of how the black light makes fluorescent objects glow. Best results are obtained in a darkened room, but this doesn't mean you have to turn off all the lights. Fig 6 [PUUTTUU] shows the arrangement of the lamps and how the shelves are constructed. The wiring diagram is given in Fig. 7. [PUUTTUU]

Again, suppose your club or church puts on some kind of performance, such as the ice ballet shown in Fig. 9. Under black lightm your perdormers can be made to appear like the one in Fig. 10. The costumes are simply a matter of sewing fluorescent silk designs to the regular wardrobe, and painting the shoes with invisible fluorescent lacquer. If you go to a theater having special fluorescent carpeting, you won't have the least trouble in finding your way down the aisle, Figs. 11 and 12, and you will enhoy the glowing beauty of fluorescent murals, such as shown in Fig 14. Fig. 13 shows an example of spongestipple technique for application of invisible fluorescent lacquer over a picture.

Costumes of fluorescent silk with applique design on skirts add novel touch to this ice ballet

Carpeting in fluorescent design eliminates groping around in theater aisles

Pictures and murals are gems of color. Example here shows sponge-stipple technique for application of invisible lacquer over picture

Signs under black light are novel in advertising. Example above shows effect of flasher system.

Not yet developed to any great extent, black light is certain to be used extensively for advertising displays and signs. Figs. 15 and 16 show an example of a small counter sign, using both white and black light. Construction of the sign is given in Fig. 17. The black light burns continuously, while the white light flashes off and on at two-second intervals. Even in ordinary room light the fluorescence is strong and distinct. This sign looks unusually well when done in plastics, but also is attractive in cabinet woods or veneer. Either thin plastic or veneer will be necessary to form the rounded lamp housings, which are open at the inner corners so that light is directed onto the picture or lettering. Figs. 18 and 19 show another type of sign of simple construction. It consists of a plywood base supporting a back in a grooved strip, and a scrolled front, which hides the lamp. Many locations are "naturals" for black light. Posters in the foyer of a theater or any sign or decoration in the dimly illuminated interior of a night club are typical. The absence of glare and visible white light has made fluorescent instrument panels a "must" on fighter aircraft, and it is expected that automobile and radio manufacturers will follow suit.

It's more than a matter of just being pretty to look at. Sorters of acetate and cellulose yarns do the job quickly and accurately because the yarns glow differently under black light although identical under white light. In culling seed beans, a bright streak of blue means that that particular bean goes in the discard since blue indicates that the non-fluorescent skin is broken, making the bean liable to disease. Hundreds of laundries have adopted black light in connection with invisible marking ink. Instead of using passout checks, many dance halls now stamp an invisible mark on the back of the hand, which glows brilliant green under black light. Prospectors on the trail of the caluable tungsten mineral, scheelite, know they have struck pay dirst when rock gives back a ghostly blue under black-light rays. Criminologists have a new weapon in black light, most spectacular being use of invisible anthracene powder, which, sprinkled on the floor or around locks, is picked up on shoes or hands of a suspect and then dramatically revealed.

The list of black-light uses is almost endless, but to get back to something anyone can enjoy, consider fluorescent minerals. It's a real thrill to collect these specimens and exhibit them to your friends. Fig. 20 gives a standard list which you can buy from any dealer. [KUVAN TIEDOT ALLA]

Principal Fluorescent Minerals
Mineral | Color at 2550 A | Color at 3600 A
Agate (Sweetwater) Green Negative
Aragonite Green Green
Autunite Yel.-Green Yel.-Green
Calcite Red or Blue Negative
Curtisite Yel.-Green Yel.-Green
Dakeite Yel.-Green Yel.-Green
Fluorite Blue Blue
Hackmanite Orange Orange
Hydrozincite Blue Negative
Opal Green Hreen
Powellite Yel. White Negative
Selenite Green Green
Scheelite Blue-White Negative
Sphalerite Orange Orange
Torbernite Yel.-Green Yel.-Green
Wernerite Negative Yellow
Willemite Green Green
Willemite and Calcite Green and Red Green

Minerals which fluoresce under black light make an interesting hobby. Light equipment should include both short and long rays. Good mineral specimens are brilliant in coloring and include all the variegations of the rainbow

Good mineral specimens are brilliant in coloring and include all the variegations of the rainbow. Light equipment should include both short and long rays. Most of the stones show brightest under short rays, such as produced by the cold-quartz lamp, but a good collection can be made of stones fluorescing at 3,600 angstroms. Fig. 21 pictures ideal light equipment - a cold-quartz lamp and black-light tubular. Less expensive, the black bulb is an excellent light source at the 3,600-angstrom level. Even the little argon will do the trick with many minerals, and a neat-looking job can be made by housing the bulb in a card-board tube, as shown in Fig. 22. The jar lid over the end of the tube permits using purple Cellophane as a filter, but this is not essential. A bottomless peek-box unit, Fig. 23, which permits examining minerals and other fluorescent objects in daylight can be made from scraps of plywood and two argon bulbs, as shown in Fig. 24.

No one style of liht is suitable for every purpose. None of the lights is truly "black," since all pass a certain amount of visible red-purple rays. This feature is subject to some control by means of the filter. A complete blackout filter cuts off all visible light but also reduces the amount of black light. The standard red-purple filter passes a small amount of visible red-purple, these rays being invisible in the presence of even a small amount of outside white light. Special heat-resisting filters are required for high-intensity mercury-vapor and other hot lamps. Cold lights such as the tubulars and argon can make effective use of purple Cellophane, lacquer films or inexpensive blue glass. All light sources given are harmless to eyes or skin except the cold-quartz lamp. The extremely short rays from this light will cause reddening of the skin similar to sunburn, hence the light must be kept away from the body when in use. The cold-quartz lamp is used mainly for showing minerals. All other lights are keyed to the 3,600-angstrom level since it is on or near this band that most paints, dyes and other products fluoresce the strongest.

The technique of using fluorescent paints is easy to master and lots of fun. You have a full range of colors, both transparent and opaque. Also, there are colorler lacquers that fuoresce white, blue and green, plus several whites which glow in different colors. paints can be obtained in either lacquer base or water color, the lacquer product being the best for most uses. The best ground is a non-reflecting white illustration board or any kind of surface painted with white or a light tint water-mix paint. Dark bases should be avoided since they weaken fluorescence. If you use a black card or cloth as a ground, first do the design with white water-mix paint, then apply fluorescent lacquer over it. Fig. 18 is an example of this technique, done in blue and yellow on a black card.

Paint technique
Both cards above are blank under white light, the clear fluorescent lacquer being invisible. Under black light , the untreated areas turn black while fluorescent backwground of Fig. 25 and letters of Fig. 26 glow blue

Combining use of invisible lacquer with a color change, black-light view of this vard shows a green outline around the black portions. At the same time, dark-pink colored portions will change to a brilliant glowing yellow

This sample shows picture change technique. White-light view is done with non-fluorescent paint, with second picture superimposed and done with fluorescent lacquer. Use non-fluorescent colors carefully for uniform fadeout

The normal method of painting is to use colored fluorescent lacquers, and the design does not change materially when viewed under either black or white light, except that it takes on a glowing quality under black light. A similar technique is used in going over non-fluorescent pictures with fluorescent lacquer. In this case transparent colors are used, as these do not conceal fine detail or shading in the original picture. Another treatment for non-fluorescent pictures or objects is to use the invisible colors. These are water-white as applied but glow brilliant blue, green and white under black light. These colors can be used for invisible pictures or signs. Figs. 25 and 26 are examples. Both of these are plain white cards under white light. Fig. 25 has the background painted invisible green; hence under black light the background glows green and the non-fluorescent letters stand out black. In Fig.26 the lettering is green and the backrgound untreated. Figs. 27 and 28 show the color-change technique where the design is one color under white light and changes color under black light. Figs. 29 and 30 show the double-picture style. This ordinarily is the most difficult to handle. An essential is that the sign or picture must be viewed in almost total darkness. The second basic rule is that the non.fluorescent paint used for the white-light effect must face out completely under black light. The right colors to use can be determined by golding colored test strips of non-reflecting cardboard or paint under the black light, picking out a set of colors that have the same darkness under black light. In this sample the ground is yellow and the lettering green; both fade out black under black light. Third basic rule is that the superimposed design must be almost entirely in line since any large use of the invisible lacquer will light up the whole panel and thus expose the original picture. A coat of clear flat lacquer over the whole panel serves as a means of cencealing the glossy highlights of the invisible picture.

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