Pinchbeck alloy is a kind of metal that is made by mixing copper and zinc together. It was invented a long time ago, in the 18th century, by a guy named Christopher Pinchbeck.
The cool thing about pinchbeck alloy is that it looks a lot like real gold, but it's way cheaper. It was used a lot back then to make jewelry and other fancy things that people wanted to look expensive, but didn't want to spend a lot of money on.
So, imagine you really wanted a gold necklace, but you didn't have a lot of money. You could get a pinchbeck necklace instead, and it would look just as shiny and pretty, but it wouldn't cost as much.
Today, people don't really use pinchbeck alloy as much because there are other metals and alloys that are even cheaper and still look like gold. But back in the day, it was a pretty big deal because it helped people who didn't have a lot of money still have nice things.