Large, South Sea mabe pearls are valuable because they are rare. Pearl farmers can only use a certain amount of wild pearl oysters per year as part of their license and can make more money from multiple pearl harvests rather than killing the oyster for the mabe. To make mabe, the oyster has a button shape implant glued to the inside of the shell and is left for nacre to grow over the top. When harvested, the mabe is cut from the oyster and the button implant is removed from the nacre coating and the mabe is filled with resin and /or glued back to a polished shell base before being set in jewelry. South Sea mabe from pinctada maxima (Australian white pearl oyster) is highly valued due to its colour and size. Mabe were very popular in the 70’s and 80’s, especially in Europe. Large, quality mabe are now mostly purchased from legacy stock in vaults these days. Example of the good stuff from Charlie Barron’s uncle, David Norman, who is based in Australia. https://aquarianpearls.com.au/product/mabe-pearl-ring-rose-gold-copy/
