If you're working on one client and need to change needle cartridges during the session, you can reuse the same tattoo cartridge. After all, you can start with a liner, then do some shading, and then conclude with more lining - as long as you complete it all in the same session and store them in a cartridge tray while not in use, you'll be OK! You should never reuse a tattoo cartridge on a different person or during a subsequent sitting. Tattoo cartridges, like needles, are single-use devices, and using them on multiple clients can readily spread bacteria and viruses such as HIV and hepatitis. When you're finished with a session, dispose of all cartridges in the properly labeled yellow sharps container!