Be very careful when using basic diamond testers or DIY jewelry testers, whether at home or even at a jewelry shop. It's important to know the limitations of each instrument and what it can and cannot do. Pen-hold diamond testers measure thermal conductivity, they were invented a very long time ago in order to separate diamonds (which had a high thermal conductivity) from very common imitations of that time- cubic zirconia and glass. These testers were not made to distinguish between natural and lab-grown diamond.
Later on, moissanite testers were developed, using technology that allowed you to measure the electric conductivity of a gemstone. This instrument was created specifically to separate moissanite from diamond, although it should be used with caution, by an experienced gemologist, as some moissanites are often tested as diamonds and vice versa, due to inconsistencies in the tester's calibration, which can change over time (as we've heard from several clients already). Moissanite testers also cannot separate lab-grown diamonds from natural counterparts.
Here at Gemcamp Laboratories, we test for natural diamond identity using an entire setup of lab-grade equipment, including a spectrometry-based instrument imported to the Philippines straight from the Gemological Institute of America in Carlsbad, California. We also employ GIA graduate gemologists and equip them with more additional gemological tools, such as the 'GIA Professional DLscope' (gemological microscope) among many others.
Be aware that basic diamond testers or moissanite testers were not made to separate lab-grown diamonds from natural stones. Our advanced laboratory setup can easily separate lab-grown synthetics from a majority of natural diamonds (type 1aAB) that exhibit characteristic spectroscopic features detectable by our machines, even if they are mounted or set into jewelry already. We can also check for lab-grown rubies, emeralds and sapphires using a suite of instruments from GIA and System Eickhorst (Germany). Our gemologist always tests your item in front of you, so you can watch, ask questions and generally learn a bit more about your item as we test it onsite.
The human eye cannot spot the difference between the kind of lab-grown diamonds coming out into the market today. These are often created by using the CVD process (Chemical Vapor Deposition), which allows more and more manufacturers to create higher qualities of pure diamond, and sell them to the public at cheaper prices compared to natural stones.
