Home › Guides › How Are Lab Grown Diamonds Made? CVD and HPHT Lab grown diamond guide How Are Lab Grown Diamonds Made? CVD and HPHT Lab grown diamonds are grown, not imitated. A small diamond "seed" is given the right carbon, heat and pressure, and the crystal grows layer by layer. There are two main methods. By Vinay Mutha, in the diamond trade in Zaveri Bazaar, Mumbai since 1999 · Updated 6 Nov 2026 On this pageStep 1 – a diamond seedMethod 1 – CVD (Chemical Vapour Deposition)Method 2 – HPHT (High Pressure, High Temperature)Is one method better?Post-growth treatmentCutting and polishingGrading and inscriptionFrom diamond to jewellery Step 1 – a diamond seed Every lab grown diamond starts with a thin slice of diamond called a seed. New carbon atoms attach to the seed in the same crystal pattern, so what grows is diamond – not glass, not CZ. Method 1 – CVD (Chemical Vapour Deposition) Seeds are placed in a sealed chamber. A carbon-rich gas (usually methane, mixed with hydrogen) is heated into a plasma. Carbon separates from the gas and settles on the seeds, building the diamond up layer by layer. A growth run takes several weeks. CVD diamonds are grown as flat, square-shaped blocks and are then cut into round, oval, pear and the other shapes. Method 2 – HPHT (High Pressure, High Temperature) HPHT copies the conditions deep inside the earth. A seed sits with pure carbon and a metal solvent inside a large press, under very high pressure and at temperatures above 1,300 °C. The carbon melts into the solvent and crystallises on the seed. HPHT is also used to improve the colour of some diamonds after growth. Is one method better? No. Both produce real diamond, and both can produce top colours and clarities. What matters for you is the finished stone: its cut, colour, clarity and carat, checked on the certificate. The IGI report states the growth method (CVD or HPHT). Post-growth treatment Some CVD diamonds are given a short heat treatment after growing to improve their colour. This is a normal, permanent process in the lab grown trade and it is disclosed on the report – for example "As Grown" (no treatment) or a note about post-growth treatment. Ask us and we will tell you exactly what your stone's report says. Cutting and polishing A rough lab grown diamond is planned, cut and polished by diamond cutters in exactly the same way as a mined diamond. Most of the world's diamonds – natural and lab grown – are cut and polished in India. A good cut is what gives a diamond its sparkle, so it is worth paying attention to the cut, polish and symmetry grades. Grading and inscription After polishing, the stone goes to a gem lab such as IGI. The lab grades it, writes a report with a unique number, and laser inscribes "LG" or "Laboratory-Grown" and the report number on the girdle (the thin outer edge). See how to read and check an IGI certificate. From diamond to jewellery We choose certified diamonds, then make your piece to order in 14K or 18K BIS hallmarked gold at our workshop in Zaveri Bazaar, Mumbai. Browse lab grown diamond rings or loose round lab grown diamonds. Frequently asked questions How long does it take to grow a lab diamond?Usually several weeks, depending on the size and the method. After that the rough stone is cut, polished and graded, which takes more time.Is CVD or HPHT better?Neither is better as such. Both make real diamond. Judge the finished stone by its 4Cs and its certificate, which also states the growth method.Are lab grown diamonds treated?Some CVD diamonds get a permanent heat treatment after growth to improve colour. It is disclosed on the IGI report. More guidesLab Grown vs Natural Diamonds: What Is Really Different?IGI Certificate Guide: How to Read and Verify a Lab Grown Diamond ReportThe 4Cs of Lab Grown Diamonds, Made Simple14K vs 18K Gold: Which Is Better for Your Diamond Jewellery?Diamond Shapes Guide: Find the Shape You LoveHow to Clean and Care for Your Diamond Jewellery