Design a site like this with
Get started


(© 2020 SLOiNVENT Copyright Notice)
“All Rights Reserved”
This includes artistic works, literary works and website content, audio and video content, software and other creative works.
Violators will be prosecuted in their country and internationally


We have chosen TWO METHODS to evaluate our “NIKOLAY II CABOCHON SAPPHIRE”:


Price comparison & Tavernier’s law gemstone calculation (comparative analysis) WITH THE CLOSEST SIMILAR COMPETITOR:

Compare our sapphire with any other sapphire you can see on the internet, keeping in mind the following facts:
-should be a sapphire that is 100% natural (no treatment),
-should be a sapphire with similar qualities declared inside an internationally recognized certificate from a world-class gemological laboratory (only Gubelin Switzerland and the GIA Gemological Institute of America are eligible),
-should be a sapphire that has international recognition and is ranked in the Guinness World Records for the simple reason that Guinness is a very strict and strict organization that issues a certificate only after a thorough verification of all data,
-and finally make a comparative analysis taking into account the size of our sapphire (13.175,00 carats = Thirteen-thousand-one-hundred-seventy-five carats) and taking into account the exponential formula (Tavernier’s law) used in the valuation of precious stones.

It is known that the price of sapphires with mass rises exponentially.

Gemstone price calculation with Tavernier’s law

Tavernier’s Law 

Generally, as a gemstone’s carat weight increases, so does the price per carat. One way to look at stone values is the following: since the late 14th century there has been a law for diamonds that is known as the ‘Indian Law’ or “Tavernier’s Law”:
Wt² x C = Price per Stone?
The following shows how the price of a gemstone might increase with this formula applied to a 5,00 US $ (*) a carat base price.
Stone weight: 13175 carats
Price of 1 carat stone of the same quality: 5,00 US $*
Calculation: 13175 x 13175 x 5 = US $ 867.903.125,00
Eight-hundred-sixty-seven-million-nine-hundred-three-thousand-one-hundred-twenty-five American dollars

*5,00 US $ / carat = The lowest possible price, and lower than the online offers for this kind of sapphires.



ABOUT GemVal – WE KINDLY WARN YOU: GemVal valuation it seems high and at first glance unrealistic. The reason for this is the fact that the so-called exponential formulas for calculating the value literally went “crazy” when the size of the sapphires was entered. Normal sizes of sapphires are in the tens or sometimes hundreds of carats, and for our sapphires, we are talking about thousands of carats … as a result, the calculation of the value is high!
Otherwise, GemVal is INTERNATIONALLY RECOGNIZED ESTABLISHMENT and if you value any gemstone of smaller or normal size (say up to 100 carats) you receive a realistic result. We have an “abnormal” situation as we are talking about a stone that is 13.175,00 carats in size (!!!).
Our valuation is visible on the official website of this institution

GemVal 02a WCG WALDHAUS NIKOLAY II Cabochon Sapphire JPG


ABOUT GemVal Official Valuation

Gemstone valuation company, which cooperates with the

Most prominent gemological, financial and government organizations in the world, among them also:

Price Waterhouse Coopers

The World Trade Center

The US Department of Homeland Security

The Australian Government

Jewelry and gemstone appraisers

Jewelry Judge
Accredited Gem Appraisers

Gemological organizations and info resources

Gemological Institute of America
Accredited Gemologists Association
American Gem Trade Association
International Colored Gemstone Association
International Gem Society
Mineralogy Club of Antwerp
Hard Assets

 Gemstone traders

Africa Gems
Paraiba International
Crescent Gems
Rare Stone
Jewelry Television
Gem Rock Auctions
Forever Gemstones
Rare and Unique Gemstones


Diamond Search Engine
Samara James
Fancy Diamonds


Opal Auctions

Brief history of GemVal


A group of gemologists and mathematicians started work on a web-based application for the appraisal of gemstones. Initially, we planned to develop a web tool to specifically evaluate natural sapphires. However after testing dozens of models, we discovered that the same statistical approach we’d developed for sapphire valuation could be applied to almost any variety of gemstone. Thus, after a year of compiling data and testing, was conceived.

2004 is launched, and 480 new users registered during its first week online!


Open Alias Corporation acquires GemVal.


GemVal offers a paid-subscription service for precious gemstones, however appraisals for most of the natural gemstone varieties remain free of charge. GemVal becomes renowned in the jewelry community.


GemVal is the first to market. We begin to publish historical-value charts, and the GemVal Aggregate index (GVA).


GemVal appointed as an approved data supplier for the provision of valuation data and pricing indices for the Market News Service, The International Trade Centre UNCTAD/WTO, Geneva.


GemVal extends its statistical database, with specific color pattern parameters added for the rare gemstone varieties.


GemVal develops the color grading system and valuation model for precious opals. GemVal releases a diamond valuation service online.


GemVal serves 1500-2000 users per day worldwide. We undertake work for gem cutters, online gemstone dealers, auction houses, private collectors, consulting institutions and governmental organizations.


GemVal is now operated by the company “Moreno Y Nicoleta” with its headquarters in Spain. New key team members join the company bringing fresh technology ideas. A new customer support system was introduced this year, payments are now accepted via PayPal and Stripe.


GemVal website undergoes a significant rebranding and redesign. Now it provides full support for mobile devices and better user experience. The accuracy of price predictions has been improved by using more data sources and changes in the core algorithm. Modern machine learning techniques and data analysis are in place to provide gemstone market insights to our customers.

2021 … coming soon !!!


GemVal system overview

There are several major stages in how GemVal system works:

-collecting data about current gemstone pricing

-training our model using machine learning techniques

-predicting price by the trained model based on user’s input

-providing insights based on statistical analysis

-data collection

We continuously add new online shops to our tracking list, so our database of gemstone pricing is steadily growing. To optimize accuracy, we make sure that only reasonable offers are entered into the database. All specimens with noticeably unusual prices are rejected and therefore have no impact upon the prediction model.

Prediction model

We are using supervised machine learning to predict gemstone values based on the specific factors influencing gem pricing – weight, color, clarity, cut and shape. The system can generalize what it learned from the collected data, and it uses this information to predict values for new input data provided by the user.


Apart from providing price prediction based on the trained model, we also analyze and publish useful insights into current gemstone markets such as weight, clarity and price distribution, for example. This information helps gemstone professionals and amateurs to educate themselves about the market and make better-informed decisions concerning trading and collecting.