The Journal

Notes on
colour.

What we learn at the bench, at the sorting table and on buying trips. Written for collectors who want to understand a stone before they own it.

An oval faceted blue topaz in deep London blue on a white background

Latest · Gem knowledge

Topaz, the November birthstone. Colours, treatments and how to care for it.

Topaz comes in almost every colour and most blue topaz is treated. Learn what is natural, what is not and why the stone needs a gentle hand despite a hardness of 8.

6 November 2026 7 min read

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Five round faceted cubic zirconia stones in red and orange tones scattered on a white surface

5 November 2026 7 min read

Glass-ceramic imitation gemstones. What GIA's 2026 study found and how labs spot them.

A new GIA study explains a convincing family of fakes that survive casting into metal and sell for under a dollar a carat. Learn how they are made, what they imitate and the tests that expose them.

An emerald cut red spinel in vivid red with bright facets, photographed on a grey background with a reflection

4 November 2026 6 min read

Red and orange spinel. What GIA's 2026 study of Mogok and Vietnam stones found.

A new Gems & Gemology study tested 127 red and orange spinel from Myanmar and Vietnam. It explains what makes the colour, which tests reveal the source and why orange stones are harder to trace.

A microscope view inside a pink gem spinel showing a large amber coloured multi phase inclusion surrounded by tiny specks

3 November 2026 6 min read

GIA origin reports in 2026. Which stones get one and what the report tells you.

Since 1 January 2026 GIA gives origin opinions on opal, peridot and demantoid garnet as well. Here is the full list of stones, what a report states and where origin testing still hits limits.

A long octagon cut tourmaline that runs from mint green to lavender pink, photographed on a white card

1 November 2026 6 min read

Watermelon and bicolor tourmaline. Why one crystal grows two colours.

A tourmaline crystal can grow pink in the centre and green on the outside. New research on nine crystals from six countries shows the cause is more complicated than manganese alone.

An Asscher cut tanzanite in deep violet blue standing on a grey background with a reflection

28 October 2026 6 min read

Tanzanite. One source, a heated blue and why you should treat it gently.

Tanzanite comes from one hillside range in Tanzania and starts out brown. Heat creates the blue, and cleavage makes it a stone for careful wear. The facts in one place.

A lime green heart shaped sphene with flashes of rainbow colour across its facets

25 October 2026 6 min read

Sphene. Why it throws more fire than a diamond and what to protect it from.

Sphene has a dispersion of 0.051, a refractive index that runs off a standard refractometer and a hardness of 5 to 5.5. The fire is the draw and the softness is the catch.

A cushion cut fuchsia pink tourmaline with a reflection on a grey background

21 October 2026 7 min read

Tourmaline, the October birthstone. Varieties, colours and what to look for.

Tourmaline covers more than thirty species and nearly every colour. Learn the variety names, the sources, the treatments and the care that suits each stone.

A cushion cut rubellite tourmaline in saturated pinkish red on a white background

18 October 2026 6 min read

Rubellite. What the name covers and what to ask about treatment.

Rubellite is pink to red tourmaline coloured by manganese. The name has no strict boundary and the treatment question is harder than most buyers expect. Here is what the research shows.

A faceted cushion cut zircon in warm golden orange resting on dark fabric

14 October 2026 6 min read

Zircon. High and low types, why blue is heated and what to check before you buy.

Zircon is a natural gem with a dispersion of 0.039, not the lab made cubic zirconia. Its hardness runs from 6 to 7.5, and radiation damage explains why.

A single imperial topaz crystal in warm orange with pink tones, photographed against a black background

11 October 2026 6 min read

Imperial topaz. The Ouro Preto story and how to read the colour.

Commercial imperial topaz comes from one area of Brazil and has been mined for about 300 years. Learn the colours, the heat question and why a torch can ruin the stone.

Four emerald cut golden yellow faceted gemstones arranged on a white surface

7 October 2026 6 min read

Gemstone treatment disclosure. What the FTC Jewelry Guides say sellers must tell you.

US rules say a seller must disclose a treatment that is not permanent, needs special care or changes the value. The same rules govern when a lab made stone can carry a gem name.

An oval faceted spessartite garnet glowing orange with a bright yellow centre, lit from behind

4 October 2026 6 min read

Mandarin garnet. Where the orange comes from and who supplies it now.

Namibia produced the first mandarin garnet in 1991 and the mine ran dry. Nigeria and Tanzania took over. The chemistry, the dates and the naming debate in one place.

A long mauve pink spinel in a fancy step cut standing upright on a grey background with a reflection below

30 September 2026 6 min read

Gemstone hardness and rings. Which stones survive daily wear and which belong in a pendant.

The Mohs scale ranks scratch resistance only. Cleavage and brittleness decide whether a stone chips or splits. Here is how spinel, topaz, tourmaline, zircon, sphene and tanzanite compare.

Two rough paraiba tourmaline crystals from Brazil, long green prisms with blue green tips, standing against a black background

27 September 2026 6 min read

Paraiba tourmaline. How one Brazilian hill and a copper surprise created a gem.

A prospector dug a hill in Brazil for years before the first blue crystals appeared in 1989. Nigeria and Mozambique followed. Here is the full story and what it means when you buy one.

A pile of rough emerald crystals, deep green six sided prisms with fine lines along their length

20 September 2026 6 min read

Nigerian emerald. What it is, where it comes from and how to buy it.

Nigeria is a small emerald producer with a big range of colour. Its stones run pale to medium green, some lean blue, and the line between emerald and green beryl matters more here than anywhere.

Gemstone shapes and cut chart showing oval, pear, cushion, rectangular, trilliant, heart, marquise, round, square and fancy outlines beside real cut stones

Buyer education

19 September 2026 8 min read

The 4Cs of coloured gemstones. What matters, and in what order.

Diamond grading gave us the 4Cs. Coloured stones use the same four words with different rules. Colour comes first, and carat weight does not tell you the size.

A deep blue violet cushion cut tanzanite in front of a purple ink splash on a white background

16 September 2026 7 min read

Tanzanite. One mine, one colour and how to judge a stone.

Tanzanite comes from a single small area in northern Tanzania. Heat creates its blue and the cutter's angle decides how much of it you see. Here is how to buy one well.

Three long emerald cut green tourmalines standing upright, each shading from lime green at the top to cool blue green at the base

13 September 2026 7 min read

Green tourmaline. Why one gem comes in so many greens.

Iron, chromium and vanadium each paint a different green. Tourmaline also changes colour along its length, and the cutter decides what you see. Here is how to choose well.

Two faceted blue green serendibites, one octagonal and one rounded, on a pale blue background

11 September 2026 6 min read

Serendibite. Found in Sri Lanka in 1902 and still almost never seen cut.

Serendibite carries a boron rich chemistry that almost never forms, and the few cut stones weigh well under a carat. Here is what it is, where it comes from and how to buy one.

Three deep blue benitoite crystals sitting in pale grey and white host rock

10 September 2026 6 min read

Benitoite. California's state gem and a blue that glows under UV light.

A prospector mistook it for sapphire in 1907. Benitoite has fire close to a diamond, glows under ultraviolet light and comes from a single mine in California.

Six faceted orange, salmon and pink gemstones in emerald, cushion, pear and step cuts on a dark reflective surface

9 September 2026 6 min read

Vayrynenite. A soft, fiery gem that almost never passes one carat.

Vayrynenite forms in a few pegmatites and glows orangey red in the right light. Almost every cut stone weighs under one carat, and the gem scratches easily.

Four Ethiopian copper-bearing tourmalines in vivid blue: an emerald cut, a rough-cut cushion, a pear shape and a large rough stone

8 September 2026 6 min read

Ethiopia joins the paraiba map. What that means for buyers.

Two major laboratories confirmed Ethiopia as a source of copper-bearing tourmaline in August 2026. The name is now settled. The price is not.

A large diaspore crystal lying on a black reflective surface, with three cut colour change stones in front of it showing green and orange tones

7 September 2026 6 min read

Zultanite. A colour change gem from one mountain range in Turkey.

Zultanite shows green in daylight and pink under a warm bulb. It cleaves easily, so cutters lose a lot of rough and finished stones ask for gentle wear.

A parcel of pink spinel rough spread on white paper, lit from one side by a gemmological torch

2 September 2026 6 min read

Spinel spent five centuries being called ruby

Two of the most famous rubies in the British crown jewels are spinel. The mix-up tells you something useful about how to buy the stone today.

Four faceted rubies resting on a rain-covered leaf, photographed against desaturated stone

Buyer education

24 August 2026 7 min read

Ruby treatments, ranked by how much they should change the price

Heat is normal. Flux healing is common. Lead glass is a different product wearing the same name. Know which one is in front of you.

A cutter holds a gemstone against a spinning polishing lap in Sri Lanka while a damp sponge sits beside it

In the workshop

15 August 2026 6 min read

What happens to a stone between the mine and the tray

A cutter decides how much of a crystal survives and how much light comes back out of it. Most of what you pay for is settled at that bench.

A grey rock of mica schist with small orange spessartite garnet crystals set into its surface

6 August 2026 5 min read

Spessartite: the orange that needs no treatment

Manganese garnet runs from warm yellow-orange to deep mandarin. Almost none of it is treated, which makes buying it refreshingly simple.

A large cushion-cut blue zircon photographed on dark leather in a shaft of warm light

28 July 2026 5 min read

Blue zircon has more fire than most people expect

Zircon disperses light almost as strongly as diamond and refracts it harder than sapphire. The trade-off is brittle facet edges.

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