It is very common to run into situations where someone wants to sell you a gold ring with diamonds or other gemstones in it. What do you do?
Option #1 is you can remove the stones before you weigh the piece of jewelry.
The pro to this approach is that you will get an accurate weight of the gold piece itself.
The Con to this approach is that unless the seller is committed to selling you the piece, they will likely be concerned about the potential damage that will be done by removing the stone or stones.
Option#2 is that you can pay based on the total weight of the piece of jewelry including the stones. Generally speaking, you will come out OK by taking this approach.
Option#3 is you can calculate the weight of the diamond and deduct it from the weight of the gold. Diamonds have a very specific weight per carat so you can measure the diamond and determine the carat weight and simply deduct that from the total weight of the piece. This approach is highly recommended for pieces of jewelry that have large diamonds in them.
The important things to keep in mind are that diamonds, unlike gold, have a VERY subjective value and the piece of jewelry that someone is selling you never came from “K-mart”. It is always from their “Aunt who smuggled out of Germany during the Holocaust” or something to that affect. So be certain to get them to sign the waiver before you attempt to remove the stone or stones.