The Blue-Ringed Octopus is one of the most venomous species of cephalopod on the planet. The iridescent blue rings are conspicuous coloration, evolved to warn potential predators away from this little octopus and its potent venom. This color ink is formulated to mimic the vibrant electric blue of the Blue-Ringed Octopus. Each bottle has 45 ml of ink, and a wide mouth for easy filling of your favorite pen.