Please DON’T EVER buy a diamond set in jewellery without a report from a reputable lab that has graded the stone out of the setting.
Jewellery valuers grade the stone in the setting and call the grade as it is seen in that setting. However, as I am sure you are aware, the colour of the metal can affect the colour of the stone quite considerably.
Colour is the most difficult characteristic to grade in a setting, and that is why is it acceptable to be at least two colour grades out when graded in a piece of jewellery. Two colour grades can make a huge difference to the price though, and the amount you are willing to pay.
It is very easy to get two different opinions in a laboratory environment using a master set with a loose diamond.
As a rule, when I was buying second-hand diamonds, I would give the client a price as seen in the setting, but it was always subject to seeing it out of the setting.
I sometimes paid them more depending on the actual weight, colour, clarity, and cut. Giving them an idea of what they could get would give them an indication of whether they would like to sell it to you or not before removing it from the setting.
The weight formulas that we use to estimate the weight of round brilliant cut diamonds are pretty accurate. Fancy cuts aren’t always as accurate.
Clarity grades are usually within a grade, but imperfections can be hidden or partly hidden under the claws or tube setting.
At the bottom of all our valuations, we state:
“Gemstones were examined in the setting and would have to be removed for an accurate assessment.”
Make sure, if you are doing valuations that you have a disclaimer of some sort to protect you and your customers..
Accredited Senior Gemologist