Article: When Nintendo released the NES in the US, the design styling was deliberately different from that of other game consoles. Nintendo wanted to distinguish its product from those of competitors and to avoid the generally poor reputation that game consoles had acquired following the video game crash of 1983. One result of this philosophy was to disguise the cartridge slot design as a front-loading zero insertion force (ZIF) cartridge socket, designed to resemble the front-loading mechanism of a VCR. The newly designed connector worked quite well when both the connector and the cartridges were clean and the pins on the connector were new. Unfortunately, the ZIF connector was not truly zero insertion force. When a user inserted the cartridge into the NES, the force of pressing the cartridge down and into place bent the contact pins slightly, as well as pressing the cartridge’s ROM board back into the cartridge itself. Frequent insertion and removal of cartridges caused the pins to wear out from repeated usage over the years and the ZIF design proved more prone to interference by dirt and dust than an industry-standard card edge connector. These design issues were not alleviated by Nintendo’s choice of materials; the console slot nickel connector springs would wear due to design and the game cartridge copper connectors were also prone to tarnishing. Many players would try to alleviate issues in the game caused by this corrosion by blowing into the cartridges, then reinserting them, which actually hurt the copper connectors by speeding up the tarnishing.

Now answer this question: What material comprised the game cartridge connectors?
copper