Auctioned Jewelry To Calibrate My Diamond Price Calculator


Auction house published information about jewelry they sell. That information can be used to help my diamond price calculator be more accurate on more rare items.

I compared my calculated diamond price to two auctioned items and was content with the SellMy.Jewelry's calculated diamond price.

Auctions are one way to really get the true value of an item. In my experience though, they are only great if two conditions are met. First, the auction house fees are minimal. Second, the auction house succeeds at gather worthy buyers in one place. Most often, only one of those conditions is met.

However, I was rummaging through jewelry auctions on the Sotheby’s auction house website recently and found some interesting data. First, it seems like Sotheby’s continually brings in worthy buyers because of the quality of the jewelry they sell on a regular basis. But poignant for my uses, I was able to calibrate and see how far off my model is.

An Honest Statement About The Diamond Price Calculator

To be honest, I do not give my model much credibility at extreme ends. What does that mean? The diamond price calculator that I built works well for diamonds I buy and sell everyday – half carat to three carat round diamonds, F to K color and VS1 to I1. It works well on most fancy cut in that range as well though not quite as well. High color (D and E) and lower color grades (M) are less accurate as are similar clarity grades. These less accurate predictions are simply because there is less information from which my algorithm can draw data and less information with which I can calibrate it.

Similarly, my algorithm does not work as well on large size diamonds. By large, I mean 6 to 10 carats. My algorithm is limited to diamonds weighing less than 10 carats.

Using The Jewelry Auction Data

By publishing their hammer price along with key information about the item, I can use that data to see how far off my algorithm is for these larger and fine diamonds. The first item I found was a 7.04 carat round brilliant diamond, F color and SI1 clarity, with a diamond report from GIA. It sold for $137,500 in New York in December 2017. SellMy.Jewelry calculated a diamond price of $121,900. I was surprised at how close I was to the price the seller received. The seller most likely received about $105,000 and the buyer paid close to $170,000 after all the fees were included. Check my information this auction house fee calculator. For my algorithm to be spot on, it should have estimated slightly less than what the buyer received. That $121,900 is within 11% of the hammer price and a good data point to know.

A second scenario I looked at yielded similar results. That one relied on a 7.41 carat round diamond G color and SI1 clarity. Here are the details.

I will continue to follow auctions in the hope that SellMy.Jewelry’s diamond price calculator can be better calibrated on these larger, fancy diamonds. For now, just an interesting comparison.

written by Joseph Dolginow

September of 2018


jewelry auctions, diamonds