Growing Colored Gemstone Crystals
Every Chatham lab-grown gemstone gets its start with a naturally- mined crystal slice placed inside a crucible chamber. We fill the chamber with a liquid containing the ingredients needed to feed crystal growth. This “liquid” is only possible at 1100 degrees Celsius! Looking into the chamber is like looking into a volcano.
Then we seal the chamber and wait. A long time. In fact, for most of the gem varieties we grow we wait from six months to a year!
The chamber’s temperature and chemistry are carefully controlled to duplicate the conditions inside the part of the earth where that gem variety forms. Slowly the crystal begins to grow on the seed in its natural crystal shape. Once this process ends, you have a crystal rough identical to one found in nature. Chatham’s gemstones contain the same physical, chemical, and optical properties as their naturally-mined counterparts.
It is still a “WOW” event every time we open up a crucible that has been untouched for 10 months. Sometimes it’s a big disappointment too. We are always experimenting by changing little things to see if we can improve the quality of our crystals. Experimentation is the key to continuing to innovate.
Every time there is an earthquake or power is lost for any sustained amount of time, crystal growth is interrupted and all the batches we are growing are lost. Any loss of power longer than 10 minutes will be visible in our crystals. This is why, although we love San Francisco, Chatham made a major decision in 1989 to diversify and grow crystals in different cities around the world. Today in addition to San Francisco, our gems are grown in France, Greece, Japan, Russia, and China.
Growing Diamond Crystals
Unlike the other gems we grow, diamond is a single element: carbon. In some ways that makes things easier. The fewer variables there are, the easier the growth process. We grow diamond using two processes: HPHT (high pressure, high temperature) and CVD, or chemical vapor deposition. In the HPHT process, we grow crystals as large as 10 carats using 50 kilobars or 725,000 PSI of pressure at 1300 degrees Celsius. If you tried to grow diamond without high pressure, you’d just get graphite. The equipment required is massive: our largest diamond press is three stories tall! It produces about 100 carats at a time in about a week to ten days. Like mined diamond, there is a lot of variety in color and clarity. Not everything we grow can be cut into a beautiful gem.
We grow fancy colored diamond crystals because of the demand for these gems. They are so rare that vivid pinks from a mine can be a million dollars or more a carat! Even though it’s very expensive to grow these gems, it’s much more affordable than natural crystals!
To grow colorless diamond crystals using the CVD process, methane gas is subjected to high-energy plasma radiation. Methane is CH4: it has one carbon atom and four hydrogen atoms. We use microwave energy heat to break the atomic bonds in the methane and free the carbon to float downand attach to a diamond seed, growing a diamond crystal atom by atom. Diamonds that grow this way can be remarkably pure.
When everything goes well, it takes about 10-12 days to produce 140 carats of crystals that are 8-9 carats each. But there are still huge technical challenges that everyone who uses this growth method faces. That’s why production of diamonds using CVD is still quite limited.
Growing diamonds is challenging and expensive. That’s why they cost only about 20% less than mined diamonds. That’s also why many companies that specialized in lab-grown diamonds that got a lot of press eventually went out of business.
From Crystal to Gem
After studying each crystal’s shape and internal inclusions, we decide which shape to cut. We cut traditional shapes and some innovative new ones like the onion cut and the flame cut that we’ve designed exclusively for our fine jewelry collection.
No matter which shape we cut, we have strict standards for proportions, faceting and polish that ensure that all our gemstones have maximum brilliance, high clarity, and vivid color. To meet these standards, 80% of the rough crystal is lost. Saving extra weight is never a consideration.
For our jewelry collection, we select one crystal in 200 that meets the strict standards for color and clarity.