Each type of ink-jet printer typically requires a specific ink cartridge to work properly. When the ink cartridge is empty, it needs to be replaced. Disposing ink cartridges can be harmful to the environment, although some printer manufactures offer a postage-free envelope to recycle the ink cartridge's casing. Many manufacturers offer services to refill the ink cartridge at a discounted rate. Kits are also sold to refill the ink cartridges at home.