LUMINOUS PAINTS.
The luminosity of minerals has an obvious practical value in the case
of such substances as can be conveniently applied in the form of a
paint to surfaces which are alternately exposed to light and darkness,
such exposed surfaces emitting at one time the light which they have
absorbed at another. Familiar illustrations are street plates, buoys,
and interiors of railway carriages having to traverse many tunnels. The
light absorbed may be either daylight or powerful artificial light.
With this object, several compositions are prepared under the generic
name of luminous paints. They are chiefly as follows:--
(1) Balmain’s.--This consists of a phosphorescent substance introduced
into ordinary paint. The phosphorescent substance employed for the
purpose is a compound obtained by simply heating together a mixture of
lime and sulphur, or substances containing lime and sulphur, such as
alabaster, gypsum, &c., with carbon or other agent, to remove a portion
of the oxygen present; or by heating lime in a vapour containing
sulphur. In applying this phosphorescent powder, the best results are
obtained by mixing it with a colourless varnish made from mastic and
turpentine; drying oils, gums, pastes, sizes, &c., may, however, also
be used.
(2) A French compound.--100 lb. of a carbonate of lime and phosphate
of lime produced by the calcination of sea-shells, and especially
those of the genus _Tridacna_ and the cuttle-fish bone, intimately
mixed with 100 lb. of lime rendered chemically pure by calcination,
25 lb. of calcined sea-salt, 25-50 per cent. of the whole mass of
sulphur, incorporated by the process of sublimation, and 3-7 per cent.
of colouring matter in the form of powder composed of monosulphide of
calcium, barium, strontium, uranium, magnesium, aluminium, or other
mineral or substance producing the same physical appearances, _i.
e._ which, after having been impregnated with light becomes luminous
in the dark. After having mixed these five ingredients intimately,
the composition obtained is ready for use. In certain cases, and
more especially for augmenting the intensity and the duration of the
luminous effect of the composition, a sixth ingredient is added, in the
form of phosphorus reduced to powder, which is obtained from seaweed by
the well-known process of calcination. As to proportion, it is found
that the phosphorus contained in a quantity of seaweed, representing
25 per cent. of the weight of the composition formed by the five
above-named ingredients, gives very good results.
The phosphorescent powder thus obtained and reduced to paste by the
addition of a sufficient quantity of varnish, such as copal, may serve
for illuminating a great number of objects, by arranging it in more or
less thick coatings, or by the application of one or more coatings of
the powder incorporated in the varnish, or by varnishing previously
and sprinkling the dry powder upon the varnish. The amount of powder
applied should not exceed the thickness of a thin sheet of cardboard.
The dry phosphorescent powders are also converted into translucent
flexible sheets of unlimited length, thickness, and width, by mixing
them with about 80 per cent. of their weight of ether and collodion in
equal parts in a close vessel, and rolling the product into sheets,
with which any objects may be covered which are intended to be
luminous in the dark. The powders may also be intimately mixed with
stearine, paraffin, rectified glue, isinglass, water glass, or other
transparent solid matter, in the proportion of 20 to 30 per cent. of
the former with 50 to 80 per cent. of either of these substances,
and this mass is then reduced into sheets of variable length, width,
and thickness, according to their intended applications. A luminous
glass is also manufactured by means of the powders, by mixing them in
glass in a fused state in the proportions of 5 to 20 per cent. of the
mass of glass. After the composition has been puddled or mixed, it is
converted into different articles, according to the ordinary processes;
or after the manufacture of an object still warm and plastic, made of
ordinary glass, it is sprinkled with the powders, which latter are then
incorporated into the surface of the article by pressure exerted in the
mould, or in any other suitable way.
It has been observed, after various trials, that the passage of an
electric current through the different compositions augments their
luminous properties or brilliancy to a great extent; this peculiarity
is intended to be utilised in various applications too numerous to
describe, but of which buoys form a good example. The current of
electricity is furnished by plates of zinc and copper mounted on
the buoy itself, when the latter is used at sea; but in rivers and
fresh-water inlets the battery will be carried in the interior of
the buoy. To secure the full effect, 10 to 20 per cent. of fine
zinc, copper, or antimony dust is added to the phosphorescent powder
described.
(3) Take oyster-shells and clean them with warm water; put them into
the fire for ½ hour; at the end of that time take them out and let them
cool. When quite cool, pound them fine, and take away any grey parts,
as they are of no use. Put the powder in a crucible with alternate
layers of flowers of sulphur. Put on the lid, and cement with sand
made into a stiff paste with beer. When dry, put over the fire and
bake for an hour. Wait until quite cold before opening the lid. The
product ought to be white. You must separate all grey parts, as they
are not luminous. Make a sifter in the following manner:--Take a pot,
put a piece of very fine muslin very loosely across it, tie around
with a string, put the powder into the top, and rake about until only
the coarse powder remains; open the pot, and you will find a very
small powder. Mix it into a thin paint with gum water, as two thin
applications are better than one thick one. This will give paint that
will remain luminous far into the night, provided it is exposed to the
light during the day.
(4) Sulphides of calcium, of barium, of strontium, &c., give
phosphorescent powders when duly heated. Each sulphide has a
predominant colour, but the temperature to which it is heated has a
modifying effect on the colour. Calcine in a covered crucible, along
with powdered charcoal, sulphate of lime, sulphate of baryta, or
sulphate of strontia; there is produced in each case a greyish white
powder, which, after exposure to strong light (either sun-light or
magnesium light), will be phosphorescent, the colour depending on the
sulphate used and the degree of heat employed.
(5) Five parts of a luminous sulphide of an alkaline earth, 10 of
fluorspar, cryolite, or other similar fluoride, 1 of barium borate;
powdered, mixed, made into a cream with water, painted on the glass or
stone article, dried, and fired in the usual way for enamels. If the
article contains an oxide of iron, lead, or other metal, it must be
first glazed with ground felspar, silica, lime phosphate, or clay, to
keep the sulphur of the sulphide from combining with the metal. The
result is an enamelled luminous article. (Heaton and Bolas.)
(6) Boil for 1 hour 2¼ oz. caustic lime, recently prepared by calcining
clean white shells at a strong red heat, with 1 oz. pure sulphur
(flowers) and 1 qt. soft water. Set aside in a covered vessel for a
few days; then pour off the liquid, collect the clear orange-coloured
crystals which have deposited, and let them drain and dry on bibulous
paper. Place the dried sulphide in a clean graphite crucible provided
with a cover. Heat for ½ hour at a temperature just short of redness,
then quickly for about 15 minutes at a white heat. Remove cover, and
pack in clay until perfectly cold. A small quantity of pure calcium
fluoride is added to the sulphide before heating it. It may be mixed
with alcoholic copal varnish. (_Boston Jl. Chem._)
The luminous calcic sulphide (also called sulphide of calcium),
now obtainable in the market, has a yellowish white tint, which
considerably limits its direct application as a paint. On the other
hand, the calcic sulphide, or the luminous paint obtained therefrom,
loses its luminous property, if it is directly mixed with the ordinary
commercial paints.
Schatte, of Dresden, produces durable white or coloured paints,
containing a luminous substance which causes them to shine in the dark,
without changing or neutralising in daylight the tint of the colouring
substance or substances contained in such paints.
For this purpose, Zanzibar or cowrie copal is melted over a charcoal
fire, 15 parts of this melted mass are dissolved in 60 parts of French
turpentine, and the resulting mixture is filtered, whereupon 25 parts
of pure linseed oil are added, which linseed oil has been previously
boiled and allowed to cool a little. The lake varnish thus obtained is
carefully treated in a paint mill with granite rollers, and worked into
a luminous paint by one of the processes hereinafter described.
Iron rollers capable of giving off under great pressure small particles
of iron, which might affect the luminous power, should not be used.
Lake varnish as obtained in commerce contains nearly always lead
or manganese, which would destroy the luminous power of the calcic
sulphide.
The proportions given are as follows:--
_Pure White_: By mixing 40 parts of lake varnish obtained as described
with 6 parts of prepared baric sulphate, 6 parts of prepared calcic
carbonate, 12 parts of prepared zinc sulphide white, and 36 parts of
calcic sulphide in a luminous condition, in an oil vessel, and worked
into a coarse emulsion, which is then ground fine between the rollers.
_Red_: 50 parts of the said lake varnish are mixed with 8 parts of
prepared baric sulphate, 2 parts of prepared madder lake, 6 parts of
prepared realgar (diarsenious disulphide), and 34 parts of calcic
sulphide in a luminous condition, and the mixture is worked in the same
way as described for white.
_Orange_: 46 parts varnish are mixed with 17·5 parts prepared barium
sulphate, 1 part prepared India yellow, 1·5 parts prepared madder lake,
and 38 parts luminous calcium sulphide.
_Yellow_: 48 parts varnish are mixed with 10 parts prepared barium
sulphate, 8 parts barium chromate, and 34 parts luminous calcium
sulphide.
_Green_: 48 parts varnish are mixed with 10 parts prepared barium
sulphate, 8 parts chromium oxide green, and 34 parts luminous calcium
sulphide.
_Blue_: 42 parts varnish, 10·2 parts prepared barium sulphate, 6·4
parts ultramarine blue, 5·4 parts cobalt blue, and 46 parts luminous
calcium sulphide.
_Violet_: 42 parts varnish, 10·2 parts prepared barium sulphate,
2·8 parts ultramarine violet, 9 parts cobalt arsenate, and 36 parts
luminous calcium sulphide.
_Grey_: 45 parts of the varnish are mixed with 6 parts prepared barium
sulphate, 6 parts prepared calcium carbonate, 0·5 part ultramarine
blue, 6·5 parts grey zinc sulphide.
_Yellowish-brown_: 48 parts varnish, 10 parts precipitated barium
sulphate, 8 parts auripigment, and 34 parts luminous calcium sulphide.
Luminous colours for artists’ use are prepared by using pure East India
poppy oil, in the same quantity, instead of the varnish, and taking
particular pains to grind the materials as fine as possible.
For luminous oil-colour paints, equal quantities of pure linseed
oil are used in the place of the varnish. The linseed oil must be
cold-pressed and thickened by heat.
All the above luminous paints can be used in the manufacture of
coloured papers, &c., if the varnish is altogether omitted, and the dry
mixtures are ground to a paste with water.
The luminous paints can also be used as wax colours for painting on
glass and similar objects, by adding, instead of the varnish, 10 per
cent. more of Japanese wax and one-fourth the quantity of the latter of
olive oil. The wax colours prepared in this way may also be used for
painting upon porcelain, and are then carefully burned without access
of air. Paintings of this kind can also be treated with water glass.