A Practitioner's Guide to Evaluating Jadeite Under Transmitted Light
1. Lighting Techniques and Beam Positioning
The angle and distance of the light change what you see more than most beginners realize. Hold it too flat and you lose texture; hold it too steep and glare hides fractures. There is no single correct position, but three setups cover most of what you need.
Direct Illumination 90° Angle
Pressing the light flat against the surface gives the deepest penetration. Use this first to get a quick read on translucency: does the light travel through cleanly, or does it die out halfway? A dense, fine-grained stone carries the glow further; a coarse one absorbs and scatters it quickly. Note: Direct light flattens internal detail—treat it as a screening pass, not a final read.
Oblique Illumination 45° Angle
This is where the real work happens. Hold the flashlight at roughly 45°, about a finger's width from the surface, and sweep it slowly. The angled beam catches the crystalline grain (cang) in a way direct light never will. Move the light a few degrees either way to distinguish genuine fine grain from surface illusion.
Backlighting Reverse Side
Position the light behind the piece and look through it. Fractures, inclusions, and cleavage planes appear as disruptions in transmitted light—where the beam meets a fissure, it stops or bends, leaving a dark shadow on the far side. Front lighting conceals these; backlighting reliably reveals them.
2. Reading Internal Texture and Crystal Fineness
How the light behaves once it is inside reflects the microcrystalline structure. This is where observation and patience outweigh simple technique.
Fine, Compact Structure
In a high-density piece, light spreads evenly—soft, consistent, and free of harsh hot spots. Grain boundaries are barely visible because crystals are tightly interlocked. The glow feels held by the stone rather than bouncing around inside it, which correlates with superior polish retention and a high-luster finish.
Coarse Structure
Large or loosely packed grains scatter light erratically in every direction. Instead of a balanced glow, you observe granular sparkles across boundaries (coarse crystalline facets). The light appears scattered and restless, indicating material that generally takes a lower polish.
3. Natural Inclusions, Veins, and Fractures
Under angled light, the primary task is distinguishing natural growth characteristics from structural damage.
Natural Growth Patterns Cotton / Mian
Almost all natural jadeite exhibits cotton—fibrous, cloudy, or snowflake-like mineral formations within the body. Under light, they appear organic and soft-edged, fully integrated into the matrix rather than cutting across it. Cotton is not a defect unless it impairs stability or translucency.
Healed Mineral Lines Stone Veins / Shiwen
These are mineral sutures formed during initial crystallization. Light passes through them with only mild refraction—the glow continues through the line without interruption. They represent geological history rather than damage, and should not be mistaken for structural cracks.
Open Fractures Cracks
A true fracture stops the light abruptly. You will see a distinct shadow or refraction barrier on the opposite side, along with sharp, angular edges. Rotating the piece under backlighting confirms this: a crack casts persistent shadows across multiple angles, whereas a healed vein does not.
A Few Practical Notes
The flashlight is a tool, not a verdict. Flawless-looking pieces can fall apart under backlight, while heavily included stones may remain completely sound because every inclusion is healed. A disciplined routine remains simple: start with direct light for screening, spend most time at 45° assessing grain, and conclude with backlighting to inspect structure. Most mistakes occur when rushing the final step.
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