Yellow sapphire — corundum coloured by iron, or by colour centres — is the stone of Jupiter (Guru) in the Navratna tradition and one of the most widely worn stones in India. Natural yellow sapphire of good, even colour is genuinely uncommon; pale, greenish and unevenly coloured material is common. That gap has been filled, for two decades, by beryllium diffusion, which turns unattractive corundum vivid yellow at low cost. A great deal of "pukhraj" on the market is treated corundum, and much of the rest is not corundum at all.
What yellow sapphire is
Corundum in any yellow shade, from pale lemon to golden to orangey yellow. Properties: RI 1.762–1.770 (two readings), SG 4.00, hardness 9, doubly refractive, weakly pleochroic, often inert under UV (some show an apricot or orange glow under long-wave, which is characteristic of certain natural yellow sapphires).
What is sold as yellow sapphire
Citrine. Yellow quartz, abundant and inexpensive. RI 1.544–1.553, SG 2.65, hardness 7. The commonest substitute; often itself heat-treated amethyst. Citrine vs heat-treated amethyst.
Yellow topaz. RI 1.61–1.64, SG 3.53, hardness 8. "Golden topaz" is a legitimate stone; sold as pukhraj it is a substitute.
Yellow glass. Singly refractive, bubbles, variable RI.
Synthetic yellow sapphire. Flame-fusion, with curved striations and bubbles; same RI and SG as natural.
Yellow zircon, yellow chrysoberyl, heliodor (yellow beryl). Each identifiable by RI and SG.
Treatments in genuine yellow sapphire
Heating. Common, to intensify or stabilise colour. Some yellow colour in sapphire comes from unstable colour centres that can fade in light; heating in an oxidising atmosphere produces stable iron-related yellow. Detected microscopically where evidence exists.
Beryllium diffusion. The defining issue for this stone. Pale or off-colour corundum is heated with beryllium-bearing material at very high temperature; beryllium penetrates deep into the stone and produces vivid yellow, orange or orange-pink. Because penetration can be complete in small stones, immersion may show nothing, and definitive exclusion requires chemical analysis (LA-ICP-MS). A bench laboratory can look for the extreme-heating signatures — melted inclusions, unusual colour concentrations — and note indications of or not excluded. Vivid yellow sapphire at a price far below unheated natural material should be assumed beryllium-treated unless a laboratory with the right instruments says otherwise. Diffusion-treated sapphire.
Irradiation. Can produce yellow that fades. Uncommon in the trade because of the instability.
How the laboratory examines a claimed pukhraj
Refractometer separates corundum from citrine, topaz and glass at once — a "pukhraj" reading 1.54 is quartz. Polariscope and dichroscope support. Microscope: natural versus synthetic; heating evidence; signs of very high-temperature treatment. Immersion for any surface colour concentration. Fluorescence noted. Report states species, natural or synthetic, and treatment — with a clear statement of whether beryllium diffusion was tested for and how.
Reading a pukhraj report
Natural corundum (yellow sapphire), no indications of heating is a premium finding. Indications of heating is common and honest. Beryllium diffusion not excluded — advanced testing recommended is what a careful bench laboratory says about a vivid stone it cannot fully characterise; it is a more useful statement than a confident "natural, heated" that did not consider the question. Quartz (citrine) means the stone was never sapphire.
Frequently asked questions
Is citrine a substitute for pukhraj?
In the traditional Upratna scheme, yes, sold under its own name. Sold as yellow sapphire, it is mislabelling — and the refractometer catches it in seconds.
Can a routine lab rule out beryllium diffusion?
No. It can note indications or their absence but cannot exclude it without chemical analysis. Ask what was done before relying on a "natural, heated" finding for a vivid stone.
Does yellow sapphire fade?
Some natural colour-centre yellow can fade with prolonged light exposure; heated iron-yellow is stable. A laboratory cannot always predict stability from a single examination.
What colour is best?
By convention, a medium, evenly saturated golden yellow without green or brown modifiers. This is a grading opinion, separate from identity.
How is pukhraj weighed for astrological use?
In carats and grams on the report; conversion to ratti is simple. Ratti, carat and gram.