Buys and Trade-in Diamonds- Double Checking Carat Weight

Whenever we take in a loose diamond on trade or as a wholesale buy in Old Town, we need to double and triple check the weight of the diamond if it is on the cusp of being right at an even carat. If it weighs 2.001ct on the diamond scale and the scale is off by .002 then it will come back as a 1.99ct when we send it off for certification, therefore making it less valuable per carat. In these cases, you must first weigh the diamond again very carefully with the scale door shut. Then have someone in the Inventory department weigh the diamond on the diamond scale in the inventory room. The person from inventory is to weigh a few other certified diamonds we have in stock to make sure the scale is weighing accurately. When there is any doubt, always buy or trade the diamond under the carat price break like .99ct or 1.99ct instead of 1.00ct or 2.00ct so we are covered.

Estate buyers in outer offices should always err on the side of caution when there is any doubt on the carat weight. Better to buy as under than over.

Air conditioning airflow can add a tiny amount to the weight of a diamond when the cover on the scale is up. That’s why we always close the cover when weighing diamonds or other valuable stones. A 1/5 of a gram (.5) doesn’t kill us, but a half of a point (.005) on a 2.00ct, 3.00ct or larger, can cost us thousands of dollars.

This policy is being written because this DID happen recently on a stone we bought as a 4.00ct that was weighed as a 4ct in house, but GIA says is a 3.99ct.

The best process, which is a multiple cross check in itself, is to:

1. Close the cover on the scale. Wait a moment.
2. Zero it with door closed. You will see 0.00
3. Open cover, put in diamond, and close again. Wait a moment and check weight.
4. Open cover, take diamond out, close cover, and wait a moment to see if it goes back to 0.00. If it doesn’t go back to ZERO POINT ZERO exactly, start over from step 1.

On significant stones of even carats, 1.00, 2.00, 3.00, and on up, it MUST be weighed on at least 2 scales, and three is even better, if you have access to them.

The way around this, if you can safely do it, and you only have one scale, is to BUY it at the .99ct price. Buying a possible 2.00ct as a 1.99ct protects you. We don’t want to cheat the customer and we certainly DO NOT want them to tell others that we buy all even weight stones as .99ct; I am saying this in case you are worried or suspect. You could become worried if you weigh a stone four times and twice it comes to an even number (3.00) and twice it weighs at 2.99ct. If your scale is “on” then this could mean it is a 2.999 and so close that the scale is struggling.

If you only have one scale, and no certificate to back up the store, and it is a high grade, you may want to do this.

Really though you should have a good scale that is weighing correctly. If you are suspect, get it checked and properly zeroed or replaced.