Tiny angled saw cuts were followed by careful cutting by a sharpened chisel on both sides to avoid splintering.One board had tiny tails, and the other had the larger pins, carefully measured to match and fit together exactly.
I like to consider it to be between 1920-1930, and that is a generally accepted period to draw the difference for jewelry. Plenty of dealers consider flapper-era jewelry antique, so think flappers and back, for simplicity.
Now, jewelry isn’t stamped with the year it was made in most cases, so dealers and buyers are forced to either learn or make mistakes.
This usually begins with looking at things like clasps and hinges, since certain types are known to have been used during specific periods in time.
The best jewelry detectives know that leftover components from earlier periods were sometimes used by frugal jewelry manufacturers, however, and clasps might have been replaced over time as well.
Or aim a flashlight as if it was a Star Wars blaster?