Ushered into the ring as“The Heaviest Typeface in the World,” StefánKjartansson’s Black Slabbath has earned its title. Kjartansson, anIceland-born designer who now runs an interactive agency in Atlanta,admits that he bestowed the superlative on the font with a note ofhyperbolic humor: Some typefaces may use more ink, but none do so asfunctionally. Released in February, the design began as an experiment topush the maximum amount of black into white space, yet still carve eachcharacter judiciously from its initial block. The letterforms fillspaces with line weights that challenge expected boundaries, pushgeometric potential, and get as thick as possible before the countersclose. When put together, letters become building blocks, modular toys.But Kjartansson maintains that the font’s real success is therhythm it achieves within such geometric simplicity, its muscle balancedwith versatile footwork. The winking play on Ozzy’s metal bandwasn’t suggested until the end of the design process, and ismerely a happy coincidence: Black Slabbath reverberates with similarintensity and volume. It’s heavy and will not equivocate.