Cut registry › Historic cuts › Portuguese
Traditional lapidary cut
The bird’s nest.
The Portuguese is not part of the brilliant’s ancestry. It is here because at 177 facets it is the extreme case, and it makes the scintillation law visible.
The short version
The Portuguese cut is a traditional lapidary design carrying 177 facets in concentric tiers, more than three times a round brilliant’s count.
It is often called the bird’s nest cut, after the dense woven pattern the tiers produce when you look into the stone.
Definition
It is not an ancestor of the round brilliant and this page does not present it as one. The five cuts in the historic line run from the single cut to the old european and end at the modern round. The Portuguese sits outside that line: a twentieth-century faceting design from the lapidary tradition, made for coloured stones as often as for diamond.
Its structure is many concentric rows of small facets on both crown and pavilion. Our reconstruction is built from a published faceting diagram rather than from a photograph or a scan, which is what makes it measurable at all.
It is included in this section because it is the extreme case. If more facets were simply better, this cut would be the best thing on the site. It is not, and the figures show exactly which terms facet count buys and which it does not.
Proportions
Trade description on the left, our reconstruction on the right. This is a faceting design rather than a graded commercial cut, so there are no standard proportion ranges to quote.
| Measure | Commonly cited | Our reference stone | What it does |
|---|---|---|---|
| Outline | round | round | Concentric tiers on both crown and pavilion. |
| Facets | 177 | 177 measured | By a wide margin the highest count we publish. |
| Depth | not standardised | 61.9% | Comparable to a modern brilliant. |
| Table | small | 48.9% | Small, to leave room for the tiers. |
| Pavilion angle | not standardised | 58° | Steep, and it costs light. |
No laboratory issues a cut grade for a Portuguese cut, and it is rarely certified at all. It is most often seen in quartz, topaz and other coloured stones, where the tier pattern is more visible than it is in a colourless diamond.
Light
Measured on the census that runs on every cut on this site: 3,200 rays face-up, 2,200 at 20° tilt, on exact facet geometry, against T57 as the standard.
| Material | Useful light | Leak | Fire | Scintillation | Global | vs the standard |
|---|---|---|---|---|---|---|
| Diamond | 84.61% | 12.67% | 65.37 | 98.04 | 86.38 | −2.23 |
| Moissanite | 82.22% | 9.98% | 95.44 | 98.04 | 91.85 | +2.03 |
| Cubic zirconia | 83.37% | 15.86% | 79.18 | 98.04 | 88.40 | −3.37 |
| T57 standard, diamond | 92.28% | 1.88% | 78.85 | 71.82 | 88.61 | 0.00 |
98.04 on scintillation, the highest figure we publish anywhere. Scintillation on this engine is 100(1−e−n/45) on the count of facets reaching the surface, and at 177 facets against the standard’s 57 this cut is close to the ceiling of that curve. There is very little left to gain from adding more.
And it does not win. Global reads 86.38 against 88.61, because the rest of the scorecard does not follow facet count. Fire falls to 65.37 against 78.85, since each of those 177 facets is small and throws a narrow spectrum that overlaps its neighbours and averages back to white. Leak runs 12.67% against 1.88%.
That is the useful lesson, and it is why this cut is worth publishing. Facet count is one term of six, it saturates, and past a point it actively costs you fire. A cut is not better for having more facets. It is better for having the right angles.
Its Index tilt figure sits at the scale ceiling of 100 and should not be read as stability.
Where the light is: useful return across the face
Five equal bands across the diameter. The Portuguese is almost perfectly even, 99.2% at the centre against 99.9% at the edges, which is the flattest profile of the six and comparable to the round-brilliant control at 99.1% against 98.1%. Many small facets in concentric tiers distribute light very evenly. They just do not return much more of it.
Against the standard
Facet count. 177 against 57, more than three times as many.
Sparkle. 98.04 against 71.82, the largest scintillation win on this site.
Fire. 65.37 against 78.85, and it loses. Small facets throw narrow spectra that overlap and read as white.
Light return. 84.61% against 92.28%, and 12.67% of leak against 1.88%.
Overall. 86.38 against 88.61. Three times the facets, and it still finishes behind a 57-facet stone from 1919.
The baseline for all of this is the round brilliant itself. Its facet plan is set out in the anatomy of a round brilliant, and the measured standard we compare against is T57, the stone Tolkowsky published in 1919.
Materials
In moissanite the Portuguese returns 82.22% for 91.85 Global with fire at 95.44, a large recovery from 65.37 in diamond. A high-dispersion material is the obvious answer to this cut’s one real weakness.
In cubic zirconia it returns 83.37% for 88.40 Global.
It is most at home in coloured stones, where the tier pattern reads clearly against a body colour. Turn it in the Index to see the pattern.
Trade-offs
Questions
The questions buyers actually ask, answered in full. Where the answer is ours to prove, the figure is measured on the Index; where it is an established gemological fact, it is stated as one.
The Portuguese cut is a traditional lapidary faceting design carrying 177 facets arranged in concentric tiers on both the crown and the pavilion. It is often called the bird’s nest cut, after the dense woven pattern those tiers produce when you look into the stone.
One hundred and seventy-seven. Our reconstruction measures 177 facets reaching the surface, against a round brilliant’s 57. It is by a wide margin the highest facet count we publish.
On scintillation, by more than any other cut we measure: 98.04 against the standard’s 71.82. Scintillation on our engine is a pure function of how many facets reach the surface, and this cut is close to the ceiling of that curve.
Because facet count is one term of six, and the others do not follow it. The Portuguese reads 86.38 Global against the 1919 standard’s 88.61: it returns 84.61% of entering light against 92.28% and leaks 12.67% against 1.88%. Angles decide light return, not facet count.
Because each facet is small. A large facet disperses light into a wide, well-separated spectrum that the eye reads as a flash of colour; a small one throws a narrow spectrum that overlaps its neighbours and averages back towards white. We measure 65.37 here against the standard’s 78.85, and against the eighteen-facet single cut’s much higher figure.
Not in the sense the rest of this section is. The five cuts in the historic line are the documented ancestry of the round brilliant, running from the single cut to the old european. The Portuguese is a twentieth-century lapidary design that sits outside that line, and it is published here because it is the extreme case for facet count.
Most often in coloured stones such as quartz, topaz and beryl, where the tier pattern reads clearly against the body colour, and in custom faceting rather than in commercial jewellery. It is rare in diamond, where the pattern is harder to see and the weight loss is expensive.
No, and this cut is the clearest demonstration of it on the site. At 177 facets against a round brilliant’s 57 it wins scintillation outright and still finishes 2.23 points behind on Global, losing on fire, on light return and on leak. What makes a cut perform is the angles, and facet count saturates.
Next
See the whole set on the historic cuts index, or the measured house and historic cuts in the cut registry.
Method
Monte-Carlo on exact facet geometry: 3,200 rays face-up plus 2,200 at 20° tilt, cosine-weighted from a 7° near-vertical cone. Useful light is what exits through the crown within 64° of vertical. The same protocol runs on every cut on this site, so the figures are comparable to each other.
They measure our reference geometry for the shape at the proportions listed above, not an average of stones on the market. A portuguese cut to different proportions will read differently. Treat them as a like-for-like comparison between shapes, not as a grade for any individual stone.
Engine estimates, ±2 points, not lab-certified grades. We do not publish the Index symmetry axis on these pages: it scores facet regularity within each pavilion family, which is meaningful for a round brilliant and misleading for a shape whose pavilion is deliberately irregular.
98.04 here against the standard’s 71.82. The term is 100(1−e−n/45) on the count of facets that actually reach the surface, so it is a pure function of facet count and nothing else.