The Bormann fuse was the invention of Charles Guillaume Bormann who was born in Saxony in 1796 and served in the Belgian army from 1832 to 1856, becoming a citizen of that country in 1841. Belgium adopted this fuse in 1935 and its efforts to keep it a military secret eventually failed. The United States tested it extensively in 1851 and soon adopted it as their primary time fuse for smoothbore artillery.
This fuse is a circular metallic disc made of equal parts lead and tin approximately 1.6 inches in diameter and 0.5 inches thick. The fuse composition, mealed powder, is compressed in a horseshoe-shaped circular channel around the circumference of the disc. The composition is securely protected from moisture or accidental ignition by a thin metal index plate marked in seconds and quarter seconds.
During field operations, the gunner cut the index plate with a sharp instrument just to the right of the desired burning time. Flame from the cannon discharge lights the fuse which burns around the horseshoe channel to zero. The flame then passes through a channel to the fuse’s small center powder magazine which explodes sending flame through the flash hole of the underplug and into the shell’s bursting charge.
The above is from Charles H. Jones' "Artillery Fuses of the Civil War" by Charles H. Jones, on page 22.