The round brilliant has 58 facets. The Portuguese cut has 160 or more — nearly three times as many, arranged in a pattern that took early twentieth-century cutters considerable effort to develop and requires more precise rough to execute.
More facets does not mean better. It means designed for different light. This distinction matters because "more facets equals a better diamond" is a common misunderstanding that the cut itself does not share.
A round brilliant returns light the way a prism breaks white light: outward, dispersed, visible across a room. The scintillation — the alternating flash of white and coloured light as the stone moves — happens in distinct, separate bursts. This is the standard brilliant experience: high contrast, high visibility, designed to perform under overhead light in bright conditions.
The Portuguese cut returns light in a denser, more layered way. With 160 facets stacked at precise angles, the reflections overlap. There is no gap between the flashes. Instead of distinct bursts, you get a continuous glow — the stone appears to generate light from within rather than redirect it from without. In direct overhead light, the difference is visible but subtle. In lower, warmer, more directional light — the light of a restaurant, a living room, an evening event — the difference becomes significant. The round brilliant dims and waits. The Portuguese cut does not.
This is not a universal advantage. If you spend most of your time outdoors in daylight, the round brilliant's performance profile is more appropriate for your conditions. If you wear your jewellery primarily at evening events — which is also when most fine jewellery is actually put on — the Portuguese cut is more useful for the light you will actually be in.
The choice between them is not a quality choice. It is a context choice. Which light will the stone live in? The answer to that question should drive the cut decision — not the facet count alone.