below pix: a boule of synthetic ruby created by flame fusion
method (at top) with cut samples (at bottom)
Synthetic (or "created") gemstones are grown in a laboratory
instead of being formed in the ground by nature. They are
physically and chemically identical to natural-grown gems but cost
much less to produce and to buy.
Just like natural gems, synthetics vary tremendously in quality.
Using low-quality processes, synthetic sapphires and rubies can be
created for less than a dollar a
carat, whereas high-quality (or "luxury")
synthetics can cost a hundred times more to create and sell for
several hundred dollars a carat at retail.
METHODS TO CREATE SYNTHETIC GEMSTONES:
Flame Fusion Method 
The first technology utilized for growing gemstones in a
laboratory, flame fusion is still very widely used to create
rubies, sapphires, and spinel. It's inexpensive, but yields low
quality gems. These created gems are often used in "class rings"
and cheap jewelry found in discount stores. It's relatively easy
for any competent jeweler to detect synthetics created by flame
fusion methods because the "dripped" molten material forms "growth
striae" (thin, narrow grooves) as it hardens
Pulled-Growth Czochralski pulled-growth is also commonly used to
create rubies, sapphires, and spinel. It's a more complex and
costly method, and creates better gems than flame fusion.
Still, both these methods yield gems of questionable quality.
Because they use very high temperatures, it is difficult for
manufacturers to achieve uniform color (particularly in rubies and
blue sapphires). The mechanical action of melting and reforming
crystals introduces non-uniformities in the gems, which scatter
light and give the stone a "dead" look - like a piece of colored
glass.
Flux Method In addition to creating the "big three" (emerald, ruby,
and sapphire), the flux method is used to grow spinel and
alexandrite. This method uses a supersaturated chemical bath to
form the crystals. Flux Method or Flux Fusion - not to be confused
with Flame Fusion - creates the highest quality and most expensive
synthetic corundum (rubies and sapphires).
Hydrothermal Method High quality emerald, as well as the less common
aquamarine, morganite, and beryl, can be lab grown by the
hydrothermal method. It uses a water solution at very high
temperature and pressure and takes several months to create a batch
of gems. That's one of the reasons higher quality created gems cost
so much more.
