Why was the 1873 blue-jeans patent not simply a patent for denim fabric?

Answer: Rivets solved stress points

Rivets solved stress points ✓ — Right. Denim work pants already existed; the famous 1873 patent by Levi Strauss and Jacob Davis covered copper rivets placed at strain points such as pocket corners and the button fly. That is a useful history twist: the iconic garment was patented as a durability hack, not as the invention of blue cloth.

A new blue dye formula — Not quite. A dye formula sounds plausible because blue is the visual signature, but the patent was not about making a new blue. Indigo dyeing long predated Levi Strauss and Jacob Davis. The 1873 legal milestone was about reinforcing pants with rivets at failure-prone spots.

A special mining cut — Not quite. A mining-specific cut would fit the Gold Rush story, but the documented invention was more mechanical than fashionable. The problem was that work pants tore at pockets and other stress points. Copper rivets strengthened those spots, turning existing workwear into a tougher product.