For making lab-grown gemstones, the constituents are dissolved in a melt or solution at high temperatures and the crystal forms initially on a seed crystal, as the melt temperature is lowered. Following table gives the comparison between various methods of gemstone creation –


 

Czochralski crystal pulling process

Flux process

Verneuil flame fusion process

Hydrothermal process

Description

Invented by Jan Czochralski and commercialized in the 1960’s.

Invented by Tom Chatham in the 1930’s.

Invented by A.V.L.  Verneuil & commercialized in the 1900’s.

Developed in the 1960’s.

Features

1. Most efficient and progressive method for obtaining high-quality & nearly flawless stones. LifeGem uses rough stones made from this process for Ruby, Alexandrite, Spinel, Chrysoberyl and Forsterite.


2. Mature technique with high optical & structural quality of gems; with uniform colouring along the whole crystal.


3. Rather expensive, as the crucibles are made of precious metals like Iridium. Growth rate is lowered to suppress the bubbles; it takes 2-3 weeks for crystal growth.


4. The process can grow single crystals of a given crystallographic orientation, without any deviation of the growth axis. High temperature gradients in the melt results in the stability of a smooth crystallization front. Growth of the crystal from the melt occurs without contact with the walls of the crucible that allows setting the geometric shape, by varying the melt temperature & pulling rate. 


5. This method produces crystals with low inner stress.

1. Slow cycle, which needs 6-12 months for growing crystals. Melted with a flux and cooled very slowly, mimicking the nature’s processes.


Worth waiting for expensive gemstones. LifeGem uses rough stones made from this process for Emerald.


2. Expensive method, as Platinum accessories & crucibles are used.


3. Un-dissolved flux results in small inclusions like natural gemstones.


4.  The product is very stable with a life-time guarantee for the colour.

 

 

1. Cheaper to produce & high rates of production; takes only a few hours to create the gemstones by melting the similar composition of minerals and colour elements with flame and dropping them into a  ‘boule’.


2.  Least expensive & most commonly used; impossible to get crystals of high quality by this method. Spread of colour & impurities are unequal in the crystals, which have curved growth & fracture porosity.


3. Difficult to control the process & to achieve the same quality. Gas bubble inclusions & cracking due to T-gradients make the gems inferior.


4. The process is subject to an open-air environment (as against a vacuum environment in other processes) and hence the crystals contain air - bubbles that trap light, diminishing the dispersion and ‘dulling’ the stones.

1.  The process is economical and takes 3 - 4 weeks to grow.


2. Cheaper containers are used, made out of steel. Crystals contain solvent impurities. For example in Emerald, the grown crystals have slightly yellowish green and fully bluish green colour, which cannot be classified as the Emerald colour. (Emerald is dark green or slightly bluish green beryl. Yellow-green beryl is called heliodor and light green beryl is just called green beryl).


3.  The minerals are subject to intense heat and pressure, in a sort of pressure cooker. Hence, the crystals contain water that affects their color and quality.