Synthetic*  diamonds,  what  is  in  a  name?  Presentation  by  Dr.  Katrien  De  Corte,  Chief  Officer  Education  &  Industry  

   The   International  Diamond  Council   defines   synthetic   diamonds   as   a   “Man-­‐made  product   that   has   the  same   chemical   composition,   crystal   structure,   optical   and   physical   properties   as   a   diamond.”   Both  natural   and   synthetic   diamonds   are  made  of   carbon,   have   the   same  density   and   refractive   index   and  share   the   same  extra-­‐ordinary  hardness.  The    main  difference   is   its  point  of  origin:  natural  diamonds  grow  deep  within  the  Earth  and  are  mostly  more  than  1  billion  years  old,  while  synthetic  diamonds  are  produced  in  a  lab  in  a  couple  of  days/weeks.  Laboratory  grown  diamonds  can  be  produced  by  two  methods.  One  is  HPHT,  under  high  pressure  and  high  temperature;  the  other  is  CVD,  chemical  vapour  deposition.        HPHT  (High  Pressure  /  High  Temperature)  

The  purpose  of  this  technique   is  to  synthetically  produce  a  diamond  by  replicating   the   formation  conditions  of  diamonds  deep  in  the  earth.   By   applying   high   pressure  (HP)   and   high   temperature   (HT)   to  a   carbon   source,   one   'forges'   a  synthetic   diamond.   Swedish  researchers   at   ASEA  were   the   first  to  produce  a  diamond  by  using  this  method   in   1953.   They   were   soon  followed  by  General  Electric  and  De  Beers.   Since   the   seventies,   gem-­‐quality   diamonds   have   been  produced  by  HPHT  synthesis.            

 CVD  (Chemical  Vapour  Deposition)  Chemical  Vapour  Deposition   (CVD)   is   the  process   through  which  a  diamond   is  produced   from  a   (carbonaceous)  gas.   The   principle   was   already   known   in   the   nineteen-­‐thirties,   but   it   took   until   the   beginning   of   this   century  

before   anyone   succeeded   in   growing   larger   single   diamond  crystals  instead  of  polycrystalline  material.      The   gas   (methane   is   usually   used)   is   heated   to   a   very   high  temperature.  Atomic  compounds  are  then  broken  down.  Then,  carbon  atoms  can  be   'precipitated'  onto  a  surface.  Under   the  right   conditions,   a   single   crystal   is   formed   that   becomes  thicker   layer   by   layer.   CVD   diamonds   are   -­‐   considering   the  complexity  of   the  process   -­‐  usually   light  brown,  making   them  relatively   unattractive   to   the   average   diamond   trader.  

   

 

However,  this  brown  colour  can  often  be  removed  using  HPHT  treatment.      Rough  synthetic  diamonds    So   far,   both   rough   HPHT   synthetic   diamonds   and   rough   CVD   synthetic   diamonds   are   easy   to   identify.   HPHT  synthetic  diamonds  grow  in  a  typical  cubo-­‐octahedral  shape  while  CVD  synthetic  diamonds  have  a  characteristic  plate  structure.      Polished  synthetic  diamonds  The  production  of   (near-­‐)   colourless  gem-­‐quality   synthetic  diamonds   improved  significantly   the   last   years.  Top-­‐quality  (D,  LC)  polished  synthetic  diamonds  are  on  the  market  today.    For  most   polished   synthetic   diamonds   visual   observation   is   not   sufficient   to   identify   the   origin   of   the   stones.  Advanced  technology  and  understanding  of  optical  centra  are  key  for  identification.    Important   to   note   however   is   that   all   colourless   synthetic   diamonds   on   the   market   have   no,   or   only   minor  amounts   of   nitrogen   while   more   than   98%   of   colourless   synthetic   diamonds   contain   nitrogen   in   their   crystal  lattice.  This  significant  difference  in  nitrogen  concentration  is  an  important  tool  to  screen  polished  diamonds.    

 CONCLUSION    In   contrast   to   diamond   imitations   (e.g.  moissanite,   CZ)   lab-­‐grown   stones   have   the   same   chemical   and  physical  properties  as  natural  diamonds.  It  is,  therefore,  in  most  cases  impossible  to  distinguish  polished  lab-­‐grown  from  natural  diamonds  by  visual  or  microscopic  examination.    

Since  full  disclosure  is  fundamental  to  consumer  confidence  it  is  important  to  use  alternative  methods  in  order  to  separate  the  lab-­‐grown  from  natural  diamonds.    

 

 

 

 

 

 

 

 

 

 

 

*For  the  purpose  of  this  presentation  the  term  “synthetic  diamond”  equals  the  terms  “Laboratory-­‐created”/  “Laboratory-­‐grown”/  “Lab-­‐grown”.