In answer to various inquiries concerning the manufacture of this article, we give herewith the process of William Henry Balmain, the original discoverer of luminous paint, and also other processes. These particulars are derived from the letters patent granted in this country to the parties named.

Balmain's invention was patented in England in 1877, and in this country in 1882. It is styled as Improvements in Painting, Varnishing, and Whitewashing, of which the following is a specification:

The said invention consists in a luminous paint, the body of which is a phosphorescent compound, or is composed in part of such a compound, and the vehicle of which is such as is used as the vehicle in ordinary paint compounds, viz., one which becomes dry by evaporation or oxidation.

The objector article to which such paint or varnish or wash is applied is itself rendered visible in the darkest place, and more or less capable of imparting light to other objects, so as to render them visible also. The phosphorescent substance found most suitable for the purpose is a compound obtained by simply heating together a mixture of lime and sulphur, or carbonate of lime and sulphur, or some of the various substances containing in themselves both lime and sulphur--such, for example, as alabaster, gypsum, and the like--with carbon or other agent to remove a portion of the oxygen contained in them, or by heating lime or carbonate of lime in a gas or vapor containing sulphur.

The vehicle to be used for the luminous paint must be one which will dry by evaporation or oxidation, in order that the paint may not become soft or fluid by heat or be liable to be easily rubbed off by accident or use from the articles to which it has been applied. It may be any of the vehicles commonly used in oil-painting or any of those commonly used in what is known as "distemper" painting or whitewashing, according to the place or purpose in or for which the paint is to be used.

It is found the best results are obtained by mixing the phosphorescent substance with a colorless varnish made with mastic or other resinous body and turpentine or spirit, making the paint as thick as convenient to apply with a brush, and with as much turpentine or spirit as can be added without impairing the required thickness. Good results may, however, be obtained with drying oils, spirit varnishes, gums, pastes, sizes, and gelatine solutions of every description, the choice being varied to meet the object in view or the nature of the article in hand.

The mode of applying the paint, varnish, or wash will also depend upon the circumstances of the case. For example, it may be applied by a brush, as in ordinary painting, or by dipping or steeping the article in the paint, varnish, or wash; or a block or type may be used to advantage, as in calico-printing and the like. For outdoor work, or wherever the surface illuminated is exposed to the vicissitudes of weather or to injury from mechanical contingencies, it is desirable to cover it with glass, or, if the article will admit of it, to glaze it over with a flux, as in enameling, or as in ordinary pottery, and this may be accomplished without injury to the effect, even when the flux or glaze requires a red heat for fusion.

Among other applications of the said invention which may be enumerated, it is particularly advantageous for rendering visible clock or watch faces and other indicators--such, for example, as compasses and the scales of barometers or thermometers--during the night or in dark places during the night time. In applying the invention to these and other like purposes there may be used either phosphorescent grounds with dark figures or dark grounds and phosphorescent figures or letters, preferring the former. In like manner there may be produced figures and letters for use on house-doors and ends of streets, wherever it is not convenient or economical to have external source of light, signposts, and signals, and names or marks to show entries to avenues or gates, and the like.

The invention is also applicable to the illumination of railway carriages by painting with phosphorescent paint a portion of the interior, thus obviating the necessity for the expense and inconvenience of the use of lamps in passing through tunnels. It may also be applied externally as warning-lights at the front and end of trains passing through tunnels, and in other similar cases, also to ordinary carriages, either internally or externally. As a night-light in a bed-room or in a room habitually dark, the application has been found quite effectual, a very small proportion of the surface rendered phosphorescent affording sufficient light for moving about the room, or for fixing upon and selecting an article in the midst of a number of complicated scientific instruments or other objects.

The invention may also be applied to private and public buildings in cases where it would be economical and advantageous to maintain for a short time a waning or twilight, so as to obviate the necessity for lighting earlier the gas or other artificial light. It may also be used in powder-mills and stores of powder, and in other cases where combustion or heat would be a constant source of danger, and generally for all purposes of artificial light where it is applicable.

In order to produce and maintain the phosphorescent light, full sunshine is not necessary, but, on the contrary, is undesirable. The illumination is best started by leaving the article or surface exposed for a short time to ordinary daylight or even artificial light, which need not be strong in order to make the illumination continue for many hours, even twenty hours, without, the necessity of renewed exposure.

The advantages of the invention consist in obtaining for the purposes of daily life a light which is maintained at no cost whatever, is free from the defects and contingent dangers arising from combustion or heat, and can be applied in many cases where all other sources of light would be inconvenient or incapable of application.