For the overview: https://www.theatlantic.com/business/archive/2012/04/the-str...
The original research paper: Margaret F. Brinig, Journal of Law, Economics, & Organization Vol. 6, No. 1 (Spring, 1990), pp. 203-215 (13 pages), https://www.jstor.org/stable/764797
Wikipedia page on Breach of Promise to Marry: https://en.wikipedia.org/wiki/Breach_of_promise
Jewelry is not a great value store, unless you're fine with selling it at a significant loss. Diamonds specially, unless they're rare, seem to magically lose a lot of its value as soon as they print your receipt.
To be honest, I find the whole love-engagement-sex-wedding handling retrograde and inappropriate for the current times.
And displaying the wealth that is mobile is also an important signal.
Pure economics would suggest a small gold bar would make more sense if you want to signal commitment.
> To be honest, I find the whole love-engagement-sex-wedding handling retrograde and inappropriate for the current times.
Me to but that is not the discussion.
Neither is a car, but they're both still very strong signals of wealth (specifically, that you could afford to burn the money).
However, if you want jewelry as a value store, you deal in gold and silver (mainly that it can be melted down)
If I buy a 3-month salary worth diamond I'm probably not gone leave you after a month.
Its an easily portable high value item that also serves as signaling for the person wearing it. It makes more sense then livestock in the modern world.
Marketing had something to do with it, but its more complex then that.