Owing to the cost of magnesium, powdered aluminum has been used to some extent as a substitute.  Aluminum does not have the illuminating value of magnesium and it is more difficult to ignite, but it is a good substitute in case of necessity.  An English mixture containing these elements is,

Barium nitrate       58 per cent. 
Magnesium            29 per cent. 
Aluminum             13 per cent.

Mixtures which are slow to ignite must be supplemented by a primary mixture which is readily ignited.  For obtaining colored lights it is only necessary to add chemicals which will give the desired color.  The mixtures can be proportioned by means of purely theoretical considerations; that is, just enough oxygen can be present to burn the fuel completely.  However, usually more oxygen is supplied than called for by theory.

The illuminating shell is perhaps the most useful of these devices to the soldier.  It has been constructed with and without parachutes, the former providing an intense light for a brief period because it falls rapidly.  These shells of the larger calibers are equipped with time-fuses and are generally rather elaborate in construction.  The shell is of steel, and has a time-fuse at the tip.  This fuse ignites a charge of black powder in the nose of the shell and this explosion ejects the star-shell out of the rear of the steel casing.  At the same time the black powder ignites the priming mixture next to it, which in turn ignites the slow-burning illuminating compound.  The star-shell has a large parachute of strong material folded in the rear of the casing and the cardboard tube containing the illuminating mixture is attached to it.  The time of burning varies, but is ordinarily less than a minute.  Certain structural details must be such as to endure the stresses of a high muzzle velocity.  Furthermore, a velocity of perhaps 1000 feet per second still obtains when the star-shell with its parachute is ejected at the desired point in the air.

The non-parachute illuminating shell is designed to give an intense light for a brief interval and is especially applicable to defense against air raids.  Such a light aims to reveal the aircraft in order that the gunners may fire at it effectively.  These shells are fitted with time-fuses which fire the charge of black powder at the desired interval after the discharge of the shell from the gun.  The contents of the shell are thereby ejected and ignited.  The container for the illuminating material is so designed that there is rapid combustion and consequently a brilliant light for about ten seconds.  The enemy airman in this short time is unable to obtain any valuable knowledge pertaining to the earth below and furthermore he is likely to be temporarily blinded by the brilliant light if it is near him.