Dark (Pyro) Aluminium: It is a very fine powder and dark grey in color. Nominal size can range from 200 mesh down to 2µ. There is a wide variety of uses for dark aluminum, for example, flash powders, star compositions, fountains, waterfalls, torches, flares, etc. For all these purposes it is generally used as a fuel. Many powders sold as “dark” aren´t really dark aluminium but the atomized type (often 63µ) and although the color of the former may vary it has to be dark grey and not light grey or even whitish grey (some of the best dark aluminium comes from Eckart Germany and this powder is nearly black in color = German Dark). Under the microscope, it´s possible to identify atomized and dark powders quite well: the former are spherical in shape while the latter are irregular and angular. Dark aluminum is generally the most expensive of all the aluminum powders.
Aluminum is a neurotoxin that alters the function of the blood-brain barrier. Additionally, small particles that are airborne act as tiny razors when they come in contact with lung or eye tissue, and a dust mask and goggles should be worn at all times when working with aluminum powder. Mixtures containing nitrates and aluminum powder are prone to heating up spontaneously and may ignite, especially when wet. This is caused by the reduction of the nitrate by aluminum, forming amides. These very basic compounds react further with aluminum powder in a very exothermic reaction that can cause spontaneous ignition. An ammonia smell is often produced in this reaction. Adding 1 to 2% boric acid to compositions containing nitrates and aluminum is common practice and will often prevent spontaneous ignition.