An article submitted for testing comes back exactly as it went in. That is not a courtesy; it is the design of the discipline. Gemmology developed its methods around the fact that the articles are valuable and must not be harmed, and every routine instrument on the bench works by observing rather than altering. Buyers who fear that testing will "damage the stone" or "affect the bead" can be reassured — and should be suspicious of any tester who proposes otherwise.
How each test leaves the article unchanged
Refractometer. A drop of contact liquid on a facet, wiped off afterwards. The liquid is a heavy oil; on porous organic materials it is avoided or used sparingly.
Specific gravity. The article is weighed in air and in water. It is dried afterwards. Porous materials (turquoise, some coral, Rudraksha) are weighed briefly or measured by other means to avoid absorption.
Polariscope, dichroscope, spectroscope. Light passes through the stone. Nothing touches it.
Microscope. Light and lenses. Immersion, where used, is in a liquid that evaporates or wipes off.
Ultraviolet. Brief exposure to UV lamps. A few materials (some topaz, kunzite) can fade under prolonged intense UV; exposures are kept to seconds.
X-ray radiography. A short exposure to X-rays. The article is not altered; there is no residual radiation; a Rudraksha or pearl can be worn immediately. The examiner is shielded; the article needs no protection.
Weighing, measuring, photographing. Contact with a balance pan, a gauge and a camera.
The exceptions, and when they are used
A few tests do leave a mark, and the laboratory uses them only when non-destructive methods have not decided the question, only on an inconspicuous spot (inside a drill hole, on the back of a cabochon, on the girdle), and only with the owner's agreement:
- Solvent swab (acetone) — to lift dye from coral or agate, or to test copal. Leaves no mark on most materials but can dull a coating.
- Hot point — a heated needle touched to plastic, horn or amber to identify by smell. Leaves a pinprick. Rarely necessary.
- Hardness (scratch) test — almost never used on a finished article. Hardness is inferred from identity. Mohs hardness and the scratch test.
- Acid — never on a finished article. Effervescence tests belong to mineralogy, not to gem testing.
If a tester proposes to scratch, burn or drop acid on an article as a routine step, they are not following laboratory practice.
What "non-destructive" does not cover
Unstringing. A mala or strand may need a bead removed for a specific test; the laboratory asks first, and re-strings or returns the bead. Most tests on strands are done strung.
Removing from a setting. A set stone can be tested in place with some limits (no SG; RI and microscope on exposed facets only). Unsetting for a full examination is the owner's decision and is done by a jeweller.
Cleaning. Heavy oil, wax or residue may be wiped from a Rudraksha or a stone so that the surface can be examined; the treatment is noted on the report.
Why it matters beyond safety
Because the tests do not alter the article, a report describes the article as it will remain. A stone tested today can be tested again tomorrow by another laboratory and give the same readings. That repeatability is what makes a report checkable, and what makes a second opinion meaningful.
Frequently asked questions
Is X-ray safe for a Rudraksha?
Yes. The exposure is a fraction of a second and leaves the bead unchanged. It can be worn straight away.
Will the refractometer liquid stain my stone?
No. It is wiped off completely. On porous organic materials it is avoided.
Can testing loosen a stone in its setting?
Handling is gentle and the setting is not stressed. A loose stone is noted on the report and should be tightened by a jeweller.
Does the laboratory ever need to cut or drill?
No. Nothing in routine testing requires cutting, drilling or removing material.
What if I want a destructive test done?
There is rarely any reason. If a specific question genuinely requires it, the laboratory will explain what, where and why, and proceed only with agreement.