I use odoo v 16, I know my question maybe is unclear so i explain in detail how i want configure it

in entrant i have a lot of unknow gemstone.

the order is identify it

so at end i can have amethyst peridot saphire and or garnet for the example

at the moment i use a order to create simulant stone  and in by produce i put all my stone with a share of 25% on each  so when i produce each one by produce the simulant have cost of 0 and is what i want. The probleme is when only one by produce and simulant is produce i have simulant got 75% of the cost .. i realy don't know how setup my process in odoo  someone can help me whit this big probleme

thanks you for your help