Given its subjective nature, grading diamonds is a complex business. But before you get down to the actual process, there are a few things to consider about your working environment that can help you arrive at a proper grading.
Let’s start with lighting. How often do you replace the light tubes in your lab/office? What colour temperature are they? For decades, the industry standard has been to use full-spectrum daylight-equivalent fluorescent light. This is a balanced, diffused, and cool white light. Typically, a bulb is classified as ‘full-spectrum’ when it has a colour rendering index (CRI) above 90 and a Kelvin temperature rating between 5500K and 6500K. Gemological Institute of America (GIA) has determined the useful life of a lamp for colour-grading purposes is 2500 hours, although it replaces its lamps approximately every 1800 hours. Therefore, if your diamond grading light is on 40 hours a week, that works out to almost 46 weeks of illumination before it is time to replace the bulbs. When grading, be sure to maintain the recommended 20- to 25-cm (8-to 10-in.) viewing distance from the light bulb. This can prevent overgrading diamonds that exhibit fluorescence, as they may react when brought closer to the bulb.
How about your wall paint?
Walk into any grading lab and you’ll likely find the walls painted white. Recently, though, GIA has recommended using neutral medium-grey, as it helps reduce eye fatigue. Various standards organizations such as ASTM International and International Organization for Standardization (ISO) also suggest neutral medium-grey walls. If you’re fond of wearing colourful clothing to work, consider putting on a white or light grey lab coat when grading diamonds to prevent colour spilling into the grading environment.
Lighting in the field
There are a few things you can do to create the right lighting environment outside your office. When I appraise a diamond or diamond jewellery at a client’s home, it’s not unusual to find myself surrounded by colourful paint or wallpaper, or to be given the option to set up on the dining room table under a dim chandelier. Instead, I use the kitchen counter near an outlet where I can ‘plug in my lab,’ which consists of portable full-spectrum lamps and a white paper base and background. When in doubt, I step outside and grade the diamond colour a second time in natural northern daylight, location, time of day, and weather conditions permitting, of course. After all, this is the type of daylight full-spectrum bulbs are attempting to mimic.