Jewellery Guides

Why To Avoid Lab Diamonds With Post-Growth Treatments

Written by Eddi Norris
August 1st, 2022 • 8 min read

What is a post-growth treatment in lab diamonds?

A post-growth treatment is used on newly grown lab diamonds that have undesirable traits, like a poor colour grade, heavy inclusions or internal graining. Diamonds that undergo these processes are called ‘treated’ or ‘enhanced’. The purpose of post-growth treatments like HPHT (High Pressure High Temperature) is to improve the quality of the diamond by getting rid of as many undesirable traits as possible - but often, it can leave the diamond looking hazy. The more post-growth treatment a lab diamond needs, the more hazy it will become. Not all lab diamonds need post-growth treatments - some are perfectly made (or very near to perfectly made), so require no touch-ups after their growth

Post-growth treatment in lab diamonds

CVD Diamonds

  • Around 90% of CVD diamonds receive post-growth treatment
  • CVD diamonds often have a brown undertone

  • They grow very fast so there is potential for spotty colour or internal graining

  • Sometimes CVD diamonds are created with boron to offset the brown tone - which can give them a blue tint instead

  • This means they commonly undergo post-growth treatment, using HPHT to improve colour and remove internal graining

  • Post growth treatments can leave diamonds look milky or hazy


  • HPHT diamonds sometimes have a blue or greyish tone

  • HPHT diamonds that need post-growth treatment essentially just undergo another round of HPHT

Why do so many lab diamonds have post-growth treatments?

Around 90% of lab diamonds made by CVD (chemical vapour deposition) look slightly brown or yellow when they are first created. As they grow so quickly, they can also be prone to internal graining, a type of undesirable diamond inclusion. This means they require post-growth treatment to get them looking up to scratch.

Lab diamonds can also be made via HPHT. Sometimes, they feature black inclusions from graphite from the process, so they need a second round in the HPHT chamber to flush these out.

Not all lab diamonds need post-growth treatments. It can take some time and effort to find lab diamonds that are ‘As Grown’ - meaning they have not received post-growth treatment - but it’s totally worth it. Lab diamonds that have had post-growth treatment are more milky and hazy than those that haven’t.

Get in touch if you’d like our experts to source a selection of lab diamonds without post-growth treatments, just for you and your personal budget.

Why should I avoid lab diamonds with post-growth treatments?

Lab diamonds that have undergone post-growth treatments often come out looking milky or hazy, meaning the diamond won’t sparkle as brightly and intensely as you’d hope. The more treatment needed, the more milky it will look. It’s a pretty simple answer - why choose a diamond with post-growth treatment when you could have one without? There’s a big chance a lab diamond without post-growth treatment will shine brighter and sparkle more intensely!

The above visualisation compares how a lab diamond could look before and after post-growth treatment - notice how the spotty brown tints have disappeared, but the diamond now looks hazy. The below visualisation compares a top quality, ‘as grown’ lab diamond that required no post-growth treatment, to a lab diamond that required HPHT to flush out colour and internal graining.

What post-growth treatments do lab diamonds undergo?


The main treatment for a lab diamond that comes out looking less than desirable is HPHT. This is used to treat CVD diamonds with poor colour or graining, and is used as a ‘second round’ for diamonds produced by HPHT that display dark inclusions.

For CVD diamonds, intense heat and pressure can cause tiny little voids, like graining, to close up and colour traces to be omitted.

Diamonds created by HPHT sometimes need a second round in the HPHT chamber. HPHT diamonds that feature black inclusions from the source graphite undergo another round of intense heat and pressure to reduce the marks. Some would argue this isn’t necessarily a post-growth treatment, but a continuation of the diamond forming via HPHT - but currently, both GIA and IGI list this as post-growth treatment.


Lab diamonds with only colour defects caused by nitrogen and nickel just need the ‘high temperature’ part of HPHT. In these cases, they’ll undergo LPHT (low pressure, high temperature) treatment to flush out the colour.

How to find a lab diamond online that hasn’t had post-growth treatment

  1. Add your search parameters to the lab diamond search tool - we typically recommend D to F colour, VS1 to SI1 clarity. Make sure to select the diamond shape you like, and a carat weight or budget range.

  2. When you’ve found a diamond you like the look of, tap ‘more info’ below the diamond’s grades.

  3. Tap ‘view certificate’, which will take you to the online IGI or GIA certificate. Here, you’ll find comments about post-growth treatments. If the certificate says ‘As Grown’, this indicates the diamond has received no post-growth treatment.

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