Manufacturer and builder 12, 1882
The introduction at this time of luminous paint is not the result of any recent discoveries or improvements in its manufacture, for we are told that the substance which Canton prepared was as good as any one can now make. Prof. Tuson, of London, has in his possession some of Canton's own make in a sealed tube, inscribed 1764, which retains its peculiar property to this day. It would seem as if the world was not yet ripe for the discovery, and it lay for more than a century a curious toy in chemical collections. Then all at once it sprung into importance, both technically and for ornamental purposes. In a lecture before the Berlin Polytechnic Society, Haedicke gave some details of its history, which may prove of interest.
All the recipes for making the luminous material depend upon the formation of sulphur compounds, sulphides of barium, strontium, or calcium. They either set out with the sulphates, which are reduced in defferent ways, or with carbonates or oxides, that are treated with sulphur or its compounds.
The Bologonian phosphorus was made, according to John, from pulverized barytes, free from iron, by mixing it with gum tragacanth to a cake, drying this and heating it for an hour between layers of coal in a wind furnace. Osann reduced the sulphate of barium by igniting it in a current of hydrogen. In 1750 Markgra heated sulhate of lime with charcoal - a method still in use to-day. Canton prepared a phosphorescent sulphur compound of lime, taking as his material burnt oyster shells, which he treated with flowers of sulphur. Grotthus attempted to improve on this method, and Osann modified it by substituting for the flowers of su[l]phur a metallic sulphide which gave up sulphur when heated, such as sulphides of antimony, tin or mercury. Wach returned to Canton's method, but mied the flowers of sulphur with small quantities of metallic oxides, such as antimony, with the view of obtaining different colors in this way. The color of the light is generally white, or, at first, bluish. Hyposulphite of strontium, or equal parts of carbonates of strontium and sulphur, when ignited for twenty or twenty-five minutes, at first over an ordinary Bunsen burner and then over the blast lamp, give a green light, while carbonate of barium and carbon give an orange-yellow light.
The pure sulphides do not give any light at all. Hence the chemical composition alone does not condition its power of giving out light, since of two substances having the same composition, one may be luminous while the other is not. It seems rather as if the power of giving light depends not only on the correct chemical composition, but also upon a definite molecular condition. Hence it happens that the luminous substance obtained from burnt mother-of-pearl is better than that from burnt oyster shells; also that when slaked lime is the material employed, the result differs from that obtained from aragonite, although in all four cases the resulting substances have the same chemical composition. The luminous material is scarcely at all attacked by common atmospheric influences.
The action of light upon such substances may be compared to striking a bell. Amomentary impulse excites it and causes the bell to vibrate and give forth a tone, which tone lasts for a certain length of time, continually growing feebler, until finally it ceases entirely. So, too, th ephosphorescent body. Excited by a momentary illumination, it gives out a bright light at first, which grows weaker and weaker, until at last it can only be perceived by a perfectly quiet eye in the deepest darkness, and at last comes to rest. The after illumination of these substances under discussion lasts much longer than the after-sound of a bell, since the waves of light are much finer than the metallic vibrations of a ringing bell.
Most sources of light will excite phosphorescence in these substances, e. g., a petroleum lamp, gaslight, and even a match. In these cases, of course the substance must be brought close to the source of light. It is excited especially by burning magnesium wire and by the electric light, but daylight is the best. Since water does not affect this substance, and since its luminosity is not due to oxodation and hence does not need the presence of atmospheric air, it will give light under water.
An alcohol lamp flame colored yellow by common salt will not exite it, but if the alcohol flame is colored blue by copper it will. In the sun's rays, those which lie in the violet and ultra-violet are the most energetic, and they decrease in power toward the yellow. It is remarkable how the yellow and red rays destroy the effect of the opposing violet rays by extinguishing or considerably weakening the luminosity caused by these latter. Similar relations prevail when the substance is covered with colored glass. Dark blue lass, although it seems to considerably weaken the light, permits all the active rays to pass through, and at times, when daylight contains many of the red and yellow rays, a substance that has been covered with blue glass is more strongly excited that if exposed to pure daylight, because the blue glass prevents the extinguishing action of the red and yellow rays. If a surface that has been covered with phosphorscent paint is first excited and then one half covered with pasteboard and the other with yellow glass, the extinguishing effect of teh latter will be very noticeable. The portion covered with pasteboard will continue luminous after that covered with glass is almost dark.
Heat has a peculiar effect upon the phosphorescent body after it has been isolated. It causes it to give a more intense light for a short time, but the luminosity is then of shorter duration than it otherwise would be. Heat acts here somewhat as it does on a magnet, driving out the active power, so that it requires to be recharged to set the power again in action.
It seems as if light bears the same relation to the phosphorescence of these bodies that electricity does to magnetism; hence the name of light-magnet would not be inappropriate.
The color of the light thrown out is independent of the color of the exciting rays - i. e., a certain substance always glows with the same colored light whether it has been excited by a violet, blue, or colorless light. Neither does the color depend on the addition of certain metals, but seems to be the result of a definite molecular condition of the substance. The light emitted retains its color but a short time. No matter how prepared, they all get to be one color after a while - that is, white (?).
The duration of luminosity is differently stated by different authors. According to Gaedicke's observation the best ones made at present time last nineteen hours; but it requires perfect darkness and an eye entirely at rest, like on waking in the morning, to detect the faint glimmer. The intensity of the light, like the sound of the bell, is greatest at first and then decreases more rapidly than it does afterward.
Its luminosity is instantly destroyed by chlorine gas, also by hydrochloric and nitric acid; more slowly by sulphuric acid. It is further destroyed by substances which darken its color, hence it cannot be mixed with varnishes that contain lead and blacken; iron is also injurious, because it rusts.
When used as a paint it is mixed with some adhesive substance like glue, and can then be mixed with oil, water or a light-colored varnish, and applied repeatedly to the object that is to be rendered luminous. It is well to prepare a white ground for it with chalk or zinc white mixed with a little copal, which may be dissolved in oil of turpentine.