Statistical analysis of gemstone web market shows that the value of faceted gemstone may be approximated by formula:
Val = (L0 + L1 * W) * W * C1 * C2 * C3 * C4
Where
L0, L1 – linear “price per carat” trend for selected gemstone variety,
W – weight
C1 – color coefficient
C2 – clarity coefficient
C3 – quality of cut coefficient
C4 – shape coefficient (for some gemstone types)
For each gemstone type the values of relevant coefficients can be derived by Least Square Method. You can valuate online your gems using free service www.gemval.com. Please report your opinion and suggestions about this web-integrated tool to info@gemval.com
Thank you and best of luck in your business!
Calo
0
Precious gemstones values
Started by Calo, May 03 2005 10:52 PM
3 replies to this topic
#2
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Cut Diamond
- Gender:Male
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Posted 04 May 2005 - 07:55 PM
That is roughly how the diamond price tool on our sister site, http://www.diamondreview.com, works. That price tool has been online since February 2000, and was developed independently by myself in early 1999.
While the tool works fairly well for 80% or so of all stones, the bad news is it doesn't work well at the extremes. The least squares method as you described it only performs linear fits, whereas real market diamond prices change exponentinally when you confound color and clarity. The result is a poor fit, and therefore a poor estimate, when you perform calculations at the extremes (for example, an FL clarity, D color stone). The tool on DiamondReview.com warns users when this occurs by assigning a confidence level to each estimate.
A more robust approach to diamond price estimation is simply to look at comparable diamonds actually being offered by dealers. That is how Diamond.Info (this site) works. Check it out at:
http://www.diamond.i...arch/search.cgi
While the tool works fairly well for 80% or so of all stones, the bad news is it doesn't work well at the extremes. The least squares method as you described it only performs linear fits, whereas real market diamond prices change exponentinally when you confound color and clarity. The result is a poor fit, and therefore a poor estimate, when you perform calculations at the extremes (for example, an FL clarity, D color stone). The tool on DiamondReview.com warns users when this occurs by assigning a confidence level to each estimate.
A more robust approach to diamond price estimation is simply to look at comparable diamonds actually being offered by dealers. That is how Diamond.Info (this site) works. Check it out at:
http://www.diamond.i...arch/search.cgi
Hermann
Moderator
Moderator
#3
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- A-List Appraiser
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Ideal Diamond
- Gender:Male
- Location:Denver Colorado, USA
Posted 05 May 2005 - 05:00 AM
Nonsense.
Calling this an appraisal is a terrible disservice to the consuming public.
Color: With all gemstones, color is a big deal. Precisely describing color is extremely difficult in the best of conditions and using the most experienced observers. The system being used here is an interesting attempt to quantify color but it is woefully inadequate, especially for the higher end stones. The difference between a $200/carat sapphire and a $2000/carat sapphire can be remarkably subtle.
Market: The market they’ve chosen to describe is for unmounted gemstones being offered for sale by online mail order houses in Asia. The values calculated don’t apply to ANY other marketplace. By using this system, consumers are lead to believe that this marketplace is representative of some other market that they may be involved in as either a buyer or as a seller. This is clearly false and they say so in the details of their report for the benefit of those who choose to read them. It’s not really their fault if a customer uses the report for a purpose other than what they intended, right? Balderdash. They know. A consumer who buys a stone in some other marketplace may be inclined to use this system to determine a ‘value’ and come to the conclusion that they paid too much or too little, probably too much. At best this is useful for customers who are buying stones from the dealers who participate in this network and would like to know how they compare to other stones being offered by those dealers. This means that this ‘appraisal’ is useless for 99% of the potential clients. For those that don’t choose to read the fine print it can lead to some seriously flawed conclusions. That said, I don’t think it’s even especially useful for the remaining 1%. Here’s why.
The pricing grid is based on dealer asking prices, not actual sales.
The grading and descriptions in the grid are by the selling dealers.
Even worse, grading on the comparison stones is being based on an examination by inexperienced consumers using unknown lighting and comparing with color swatches displayed on a monitor. There are even people who think this might be useful for examining a photograph taken by a 3rd party and included in an online auction!
There is no value component associated with either the location of the stone or the credibility of the dealer despite the observation that these have a tremendous effect on the buyers and their willingness to pay a particular price.
Buying gemstones without examining them is, in my opinion, a risky proposition. It shouldn’t be done without first assessing the merits of the dealer, including their selling and return policies and your personal prior history with them. Relationships matter. There are quality dealers that advertise online and probably even some that participate in this pricing scheme but pretending that such a system is an appraisal is, in my opinion, irresponsible.
Neil Beaty
GG(GIA) ISA NAJA
Calling this an appraisal is a terrible disservice to the consuming public.
Color: With all gemstones, color is a big deal. Precisely describing color is extremely difficult in the best of conditions and using the most experienced observers. The system being used here is an interesting attempt to quantify color but it is woefully inadequate, especially for the higher end stones. The difference between a $200/carat sapphire and a $2000/carat sapphire can be remarkably subtle.
Market: The market they’ve chosen to describe is for unmounted gemstones being offered for sale by online mail order houses in Asia. The values calculated don’t apply to ANY other marketplace. By using this system, consumers are lead to believe that this marketplace is representative of some other market that they may be involved in as either a buyer or as a seller. This is clearly false and they say so in the details of their report for the benefit of those who choose to read them. It’s not really their fault if a customer uses the report for a purpose other than what they intended, right? Balderdash. They know. A consumer who buys a stone in some other marketplace may be inclined to use this system to determine a ‘value’ and come to the conclusion that they paid too much or too little, probably too much. At best this is useful for customers who are buying stones from the dealers who participate in this network and would like to know how they compare to other stones being offered by those dealers. This means that this ‘appraisal’ is useless for 99% of the potential clients. For those that don’t choose to read the fine print it can lead to some seriously flawed conclusions. That said, I don’t think it’s even especially useful for the remaining 1%. Here’s why.
The pricing grid is based on dealer asking prices, not actual sales.
The grading and descriptions in the grid are by the selling dealers.
Even worse, grading on the comparison stones is being based on an examination by inexperienced consumers using unknown lighting and comparing with color swatches displayed on a monitor. There are even people who think this might be useful for examining a photograph taken by a 3rd party and included in an online auction!
There is no value component associated with either the location of the stone or the credibility of the dealer despite the observation that these have a tremendous effect on the buyers and their willingness to pay a particular price.
Buying gemstones without examining them is, in my opinion, a risky proposition. It shouldn’t be done without first assessing the merits of the dealer, including their selling and return policies and your personal prior history with them. Relationships matter. There are quality dealers that advertise online and probably even some that participate in this pricing scheme but pretending that such a system is an appraisal is, in my opinion, irresponsible.
Neil Beaty
GG(GIA) ISA NAJA
Neil Beaty
GG(GIA) ICGA(AGS) NAJA
There's never a crowd when you go that extra mile.
Professional Appraisals in Denver
GG(GIA) ICGA(AGS) NAJA
There's never a crowd when you go that extra mile.
Professional Appraisals in Denver
#4
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Cut Diamond
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Posted 05 May 2005 - 09:27 AM
I completely agree that calling such a report an "appraisal" is a disservice to consumers. You will not find that word used in anything we do here.
Consumers, desperately seeking a definitive answer to the question of value, will tend to overrely on the results of a flawed report. Although the statistical method s/he describes seems promising on paper to a math guru or an engineer, the reality is much different.
I'm curious what you think of the diamond comparison approach such as what is done here on Diamond.info?
Consumers, desperately seeking a definitive answer to the question of value, will tend to overrely on the results of a flawed report. Although the statistical method s/he describes seems promising on paper to a math guru or an engineer, the reality is much different.
I'm curious what you think of the diamond comparison approach such as what is done here on Diamond.info?
Hermann
Moderator
Moderator
