Cut registry › Historic cuts › Old Single
Historic cuts · The beginning
Where the brilliant starts.
The single cut is the first recognisable ancestor of the round brilliant, and the only one of the six still cut commercially today.
The short version
An old single cut diamond, also called the eight cut, is a simple faceted round with eight facets on the crown, eight on the pavilion, a table and a culet: 18 facets in total.
It is the oldest faceted diamond design still in regular production, because at very small sizes a fuller facet plan buys nothing the eye can resolve.
Definition
The single cut was reached by taking the medieval table cut, a squared-off octahedron, and smoothing its four corners into an octagon. That produced eight crown facets around a table and eight matching pavilion facets. It has been made since roughly the 1300s.
It is not obsolete. Melee diamonds under about 0.02 carats are still routinely cut as singles, because below that size a 57-facet plan produces facets too small to throw a distinguishable flash, and cutting them wastes time and weight for no visible gain.
Tolkowsky does not describe it directly in Diamond Design. He implies it: the double cut of the following century has sixteen facets on the upper side, so the cut it improved on had eight. The geometry here is built from that implication rather than from a drawing.
Two facet counts, and both are right. The historic count omits the girdle, because a hand-bruted stone had no faceted girdle to count. Our model resolves the girdle as real surfaces, so the census reads 26. Where a figure below depends on facet count, it is the measured number that produced it.
Proportions
Trade convention on the left, our reconstructed stone on the right. The single cut has no modern proportion standard, so the left column is descriptive rather than prescriptive.
| Measure | Commonly cited | Our reference stone | What it does |
|---|---|---|---|
| Outline | regular octagon | regular octagon | Eight sides, from smoothing a square table cut. |
| Historic facets | 18 (9 crown, 9 pavilion) | 26 measured | The difference is the girdle. |
| Depth | not standardised | 67.5% | Deep by modern standards. |
| Table | not standardised | 57.5% | The flat top, as a share of the width. |
| Pavilion angle | not standardised | 48.5° | Far steeper than the modern 40.75°. |
No laboratory issues a cut grade for a single cut, and none ever has. At the sizes it is used today it is almost never certified individually either: melee is bought by parcel, matched to a size and a quality range.
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 | 72.11% | 19.30% | 84.19 | 43.89 | 78.79 | −9.82 |
| Moissanite | 76.64% | 12.47% | 98.80 | 43.89 | 83.18 | −6.64 |
| Cubic zirconia | 65.37% | 27.33% | 83.33 | 43.89 | 75.80 | −15.98 |
| T57 standard, diamond | 92.28% | 1.88% | 78.85 | 71.82 | 88.61 | 0.00 |
The single cut returns 72.11% of entering light usefully against the round brilliant standard’s 92.28%, and scores 78.79 Global against 88.61. On 26 measured facets it scores 43.89 on scintillation, the lowest of the historic cuts and far below the standard’s 71.82.
What is surprising is the fire. At 84.19 against the standard’s 78.85, an eight-facet stone throws more colour than Tolkowsky’s ideal does. Large facets split light into wide, well-separated spectra; small ones produce many narrow flashes that overlap and read as white. The single cut has no sparkle and a great deal of colour, which is exactly how old stones look under a candle.
It also holds movement well, at 93.60 against 90.41. Its weakness is leak: 19.30% against the standard’s 1.88%, from a pavilion of 48.5° that is far steeper than the critical angle wants.
Where the light is: useful return across the face
Five equal bands across the diameter, each returning ray binned by the point on the crown it leaves through. The single cut returns 86.1% at the edges against 65.9% in the centre, so the middle of the stone is the dark part. A round brilliant is flat, 98.1% against 99.1%. That dark centre under a wide table is the effect the trade calls a window, and on this cut it is structural rather than a fault.
Against the standard
Facet count. 26 measured against the standard’s 57, and 18 against 58 on the historic count. Everything below follows from that.
Sparkle. 43.89 against 71.82 on scintillation. A single cut produces a handful of large flashes where a brilliant produces a shower of small ones.
Fire. 84.19 against 78.85. The single cut wins this one, and it is the only historic cut here that beats the modern standard on any headline term.
Light return. 72.11% against 92.28%. Six centuries of cutting bought most of that difference.
Where you meet one. Not as a centre stone. As melee, in the pavé of a modern ring, cut this way on purpose.
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 single cut returns 76.64% for 83.18 Global with fire at 98.80, the highest fire figure of any historic cut in any material we measure. A high-dispersion material with very large facets is the strongest possible combination for colour.
In cubic zirconia it returns 65.37% for 75.80 Global.
Turn one in the Index and the difference from a brilliant is immediate: you can count the flashes.
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.
A single cut diamond, also called an eight cut or old single cut, is a round stone with eight crown facets, eight pavilion facets, a table and a culet, giving 18 facets in total. It was reached by smoothing the four corners of a square table cut into an octagon, and has been made since roughly the 1300s.
Eighteen by the historic count: nine on the crown including the table, nine on the pavilion including the culet. Our reconstruction measures 26 facets that actually reach the surface, the difference being the girdle, which a hand-bruted stone did not carry as countable facets.
Yes, and not as reproductions. Melee diamonds below roughly 0.02 carats are routinely cut as singles, because at that size a 57-facet plan produces facets too small to throw a flash the eye can separate. It is the right cut for the job rather than an obsolete one.
It returns 72.11% of entering light against the standard’s 92.28% and scores 43.89 on scintillation against 71.82. It beats the standard on one term: fire, at 84.19 against 78.85, because large facets split light into wide, well-separated spectra.
Facet count and nothing else conceptually. A single cut carries 18 facets, a full cut 57 or 58. In melee parcels the two are priced and sold separately, and a full cut of the same size costs more because it takes longer to make.
Because its facets are large. A large facet disperses light into a wide, well-separated spectrum that reads as a distinct flash of colour. Many small facets produce many narrow spectra that overlap and average back towards white. We measure the single cut at 84.19 fire against the modern standard’s 78.85.
It is the oldest faceted design still in production, but not the oldest cut. It descends from the table cut, which was simply a natural octahedron with one point ground flat, and that in turn from the point cut, which was the natural crystal polished but not reshaped.
At the start of it. Tolkowsky does not describe it directly in Diamond Design, but he implies it: the double cut that followed has sixteen facets on the upper side, so the cut it improved on had eight. The Mazarin doubled it, the Peruzzi doubled it again, and the modern round brilliant is what that line arrived at.
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 old single 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.
43.89 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.