Brown powder or prismatic powder, sometimes referred as "cocoa powder" due to its color, is an explosive agent similar to black powder, but with a slower (and therefore gentler) burning rate. This difference is achieved by incorporating fuel ingredients that are in a less-reactive state; the pulverized and fully processed charcoal (elemental carbon) in black powder provides its distinctive color while its replacement with a different substance produces a more reflective powder, hence its own namesake color. Further modifications of burn rate are made possible by shaping the individual powder grains, often into prismatic shapes such as single-perforated hexagonal or octagonal prisms. [1]
Prismatic powder was introduced in the 1850s by US Army Major Thomas Rodman. By 1880 naval guns were using "powder" made of prisms one inch in height.[2] Very large grain powered was dangerous however due to occasional pressure irregularities as demonstrated in the 1880 accident on the Italian ironclad Caio Duilio (which used Fossano powder).[3] In 1884 the German Rottweil Company developed Prismatic Brown Powder (PBC), which was adopted by the Royal Navy in 1884. The French navy instead developed the Slow Burning Cocoa (SBC) powder, which had grains of about 3.1 millimeters; still only 40% of it burned, the rest was ejected as heavy black smoke. All these were rendered obsolete in 1886 when the first smokeless propellant, the guncotton-based Poudre B was developed, triggering rapid development of other smokeless compounds. Some Royal Navy ships like the Royal Sovereign class battleships were commissioned with the already obsolete SBC-based guns, but the subsequent Majestic and Canopus class battleships were the first to adopt cordite Mk I.[2]
For pure explosive damage, high burn rates or detonation speeds (and accompanying brisance) are generally preferable, but in guns and especially cannons, slower-burning powder decreases firing stresses. This allows for lighter, longer (and more accurate) barrels with associated decreases in production and maintenance costs.