We wanted zamac. Zamac is a zinc alloy, it is what the heavy caps on expensive bottles are made of, and at the volume we needed it was not economically sourceable. That is the entire story of why the cap is not metal.What we used instead is an acrylonitrile-based polymer, machined and weighted. The finished cap comes in at twenty-four grams.Twenty-four was not a target. It is what the cap weighed once it stopped feeling hollow. Hollowness is the thing that gives a cheap cap away, and it is not really about mass, it is about sound. A light cap makes a plastic noise when it meets glass. Past a certain density that noise changes and becomes a click.The magnet was the second problem. A cap that has to be pushed and turned is a cap that gets left off. A cap that pulls itself the last few millimetres and seats in one position gets put back on every time. Alignment matters here: the label has to land the same way up, which means the magnet cannot simply hold, it has to index.We went through more prototypes on the cap than on most formulas. None of that is visible in a photograph, which is a recurring problem with objects.