The 50% tariff on imported copper that starts Friday excludes a critical input that companies say they can’t get enough of in the U.S.: cathodes. Here's what you need to know. What are cathodes? Cathodes are a key intermediate product in copper manufacturing.

The once-mighty premium U.S. copper enjoyed over the global benchmark slid on Thursday as markets clawed back months of gains in hours of frenzied trading after President Donald Trump surprised markets with pared-back tariffs.

The global copper market is reeling from its biggest shock yet in a year of policy surprises, violent price swings and unprecedented trade dislocation.