Every few months the Zorn palette discussion starts again. One side says four tubes (yellow ochre, cadmium red light, ivory black, titanium white) taught them more about colour than years of buying paint. The other side says it is a portrait trick that falls apart the moment you point it at a June landscape. Both are right. The reason they never convince each other is that they are having a gamut argument without drawing the gamut.
A palette’s gamut is the set of colours it can physically mix. Not the colours on the tubes, but the whole territory reachable by combining them in any proportion. Every palette has one, it has a definite shape, and almost nobody has seen theirs. We argue about limited palettes the way you would argue about a country’s borders without a map.
So I have drawn the map for this one, below.
What the four tubes are
First, be precise about the members, because the internet is not. Anders Zorn’s working palette, at least in the studio setups and self-portraits we have, was yellow ochre, vermilion, ivory black and lead white. The modern convention substitutes cadmium red light for vermilion and titanium white for lead. Both substitutions matter a little. The cadmium is noticeably stronger in mixes than vermilion was, which is why Zorn-palette flesh mixes go shouty if you treat the red as an equal partner rather than a seasoning.
The famous move is that ivory black plays the part of blue, and that is meant literally. Ivory black has a cool, faintly blue undertone. Let it down with white and you get a convincing slate blue-grey. Mix it into yellow ochre and you get a respectable range of muted greens, from olive drab to something close to terre verte. Seen that way the palette is a warm yellow, a warm red, a very desaturated cool blue, and white.
The shape of the territory
Put those four through pigment-mixing maths (Kubelka–Munk, the physics of how real paint scatters and absorbs light, rather than the additive blending a screen does) and the gamut has a distinctive shape. Halftint computes this from whatever tubes you own. Here is the Zorn wheel at three values:
The territory is a lopsided wedge. It bulges through the warm side: oranges, terracottas, golden umbers, and a large, finely graded region of flesh. Every half-tint between light and shadow on skin sits comfortably inside the borders. Values run the full range from near-black to white. Down the cool side, the wedge thins to a corridor of low-chroma blues and greens: slate greys, olive and drab greens, smoke colours.
Then there is everything outside the line. No mixture of these four tubes produces a cerulean summer sky at full strength. Red plus black-as-blue gives plum-coloured mud rather than violet, and the engine puts the nearest reachable mix a long way from a true violet (ΔE 21.8, a difference you would spot from across the room). No spring green, no teal, nothing saturated on the far cool side. The full list of what is out, with the closest mix and the distance for each, is on the Zorn palette page.
Why both sides are right
Seen this way, the two sides turn out not to be disagreeing about the same thing.
The portrait painters are right because their subject lives inside the wedge. Skin, hair, most interior shadow, candlelight, north light on a white shirt: the chroma demands of a portrait are modest and warm-biased, and the Zorn gamut covers them with room to spare. Within its borders, four tubes are an advantage. Every mix is two or three decisions, everything harmonises because everything shares parentage, and you learn value discipline because black is sitting right there teaching it.
The landscape painters are right because their subject doesn’t. A sunlit meadow in May asks for greens the wedge cannot reach at any mixing ratio. You can knock the scene down into a tonalist key and make a lovely painting, and plenty have, but that is choosing to move the subject inside your borders. It is not proof the borders weren’t there.
Put more plainly, a limited palette is a territory, and the question that matters is whether today’s subject lives inside it.
Using the map before you paint
This is the practical habit worth stealing, and it needs nothing fancy. Before a session, ask what the most saturated notes in your subject are and whether your palette can reach them. With experience you can estimate it. With a computed gamut you can look. Load the four Zorn tubes in Halftint and the wheel shows the wedge directly. If you pick a target outside it, it tells you so, shows the closest mix it can make with the distance stated, and names the single tube that would close the gap. For the classic Zorn holes that rescue tube is usually ultramarine or cobalt for the violets and sky blues, or a green like viridian for the saturated greens. A Zorn-plus-one palette of five tubes covers a surprising amount of the world.
None of this diminishes the exercise. Painting inside a small territory for a month is still the best colour-mixing education I know of. You learn what black is made of, you learn that flesh is mostly grey, you learn restraint. Do it, but do it knowing the borders are real and drawn by pigment physics rather than by effort or attitude. The painters who say you can mix anything with the Zorn palette have been painting subjects that live inside the wedge. The painters who call it restrictive have been standing outside it, pointing at a sky the palette will never reach.
It helps to draw the map before the argument starts.