The Sheaffer Skrip Pen Ink Cartridge Refills in Black & Blue include eight blue cartridges and one black cartridge, all made of plastic. These high-quality cartridges provide a smooth writing experience with both black and blue ink options, making them versatile for various writing tasks. Perfect for collectors or those looking to replenish their pen ink supply, these cartridges are a reliable choice for anyone in need of ink refills.