NFC (Near Field Communication) tags generally do not work well directly on metal surfaces. This is because metal can interfere with the radio frequency signals used by NFC technology. The metal can reflect and absorb the electromagnetic fields, preventing the proper communication between the NFC tag and the reading device.

To overcome this issue, special NFC tags designed for use on metal surfaces are available. These tags typically have a protective layer or barrier that helps to shield them from the metal interference. They may also be designed with a gap or spacer to create a small distance between the tag and the metal surface, allowing for better NFC functionality.

If you need to use NFC tags on metal objects, make sure to select tags specifically designed for such applications. These are often referred to as "on-metal" or "metal-friendly" NFC tags. Always check the product specifications and recommendations from the tag manufacturer to ensure proper performance in your specific use case.