14. First, let me impress upon you the necessity of seeing that _all
ingredients used in star compositions are in as fine a powder as
possible_. You cannot have them too fine or too well incorporated and
mixed. The following is the formula which I employ for the
COMMON BRILLIANT STARS.
Nitre 16 parts
Sulphur 8 „
Sulphuret of antimony 4 „
Meal-powder 3 „
Let all these ingredients be in fine powder, and, having carefully
weighed out the quantities, mix them thoroughly. Next, take some
gum-water of the strength previously mentioned—viz., two ounces of
gum-arabic dissolved in a pint of warm water. Spread your star
composition upon a piece of zinc plate or slate, and add to it a little
of the gum-water at a time, taking care to stir the composition about
_well_ till all the moisture is equally diffused through the whole. It
is not necessary that this composition should be made _wet_, but only
something like brown sugar in moistness, so that it will _bind well_
when pressed together. When you think this is sufficiently done, roll or
press the composition into a flat shape like a thick pancake, and make
it as square, or, at all events, as rectangular, as possible. Its
thickness should be about _a quarter of an inch_. You will find a large
spatula a very convenient tool in this operation, both for flattening
the cake of composition and for getting it into a convenient shape. Now
take your spatula, and with it score the composition across both ways,
so that you have it divided into a number of little cubes, fig. 30.
It may then be set aside to dry in a warm place; it will be forty-eight
hours before it is fit for use in summer, and about a week in winter.
When dry you will have no trouble in separating the cubes at the marks
left by the spatula.
[Illustration:
Fig. 30.
]
I may as well, however, introduce you to a simple piece of apparatus
which will enable you to perform this operation much more comfortably
and cleanly. I have a small wooden tray made of mahogany, six inches
square, and three-quarters of an inch deep, _inside measurements_. Into
this I place a flat piece of wood, which fits very easily into the tray,
and is half-an-inch thick. This acts as a _movable false bottom_. It
will be readily seen that when this false bottom is in the tray, placed
upon the other bottom, _the tray will be filled up so as to leave a
depth of a quarter of an inch only unoccupied_. This space I fill with
the moistened star composition, having first rubbed the surface of the
false bottom with soap to prevent any adhesion taking place between the
composition and the wood. Having now pressed into the tray as much
composition as will fill it to the height of its sides, I score it with
the spatula as directed above. A large hole is made in the _natural_
bottom of the tray, so that I can, by putting my fingers through it,
raise the false bottom covered with stars out of the tray. I then place
a piece of cardboard or zinc on the top of the stars and turn the false
bottom upside down. The stars will be found to separate from the wood
very easily, and may be left to dry on the zinc. The tray is then ready
for another batch of stars.
The advantages of this plan are, that there is no trouble in getting the
composition into a uniform, convenient shape and thickness; that the
composition requires much less gum-water; and that, consequently, the
process is a quicker and a cleaner one.