Most oil painters own titanium white and nothing else, which is fine until the first time a tint comes out chalky and they cannot say why. The reason is usually not the colour. It is the white.

Two pigments, one job

Titanium white is PW6, titanium dioxide. It is the most opaque, highest-scattering pigment on the palette, which is another way of saying it is the strongest white: a little of it lightens a lot. Zinc white is PW4, zinc oxide. It is semi-transparent and much weaker, roughly half the tinting strength in Halftint's data (titanium 1, zinc 0.55 on the scale where an average tube is 1). Lead white, where you can still buy it, sits between them and has a warmth of its own.

The same tints, side by side

These tints were mixed with Halftint's engine: one part of the colour to one, three and seven parts of each white, by amount. The last column is how far apart the two 1:3 tints land, in OKLab units times 100; anything over 3 is a visible difference.

Colourwith titanium whitewith zinc whiteDifference at 1:3
  • Ultramarine Blue
  • 1:1
  • 1:3
  • 1:7
  • 1:1
  • 1:3
  • 1:7
 ΔE 8.8
  • Cadmium Red Light
  • 1:1
  • 1:3
  • 1:7
  • 1:1
  • 1:3
  • 1:7
 ΔE 8.6
  • Yellow Ochre
  • 1:1
  • 1:3
  • 1:7
  • 1:1
  • 1:3
  • 1:7
 ΔE 5.6
  • Viridian
  • 1:1
  • 1:3
  • 1:7
  • 1:1
  • 1:3
  • 1:7
 ΔE 7.4

At every ratio the zinc tint is darker and keeps more of the colour. The titanium tint is paler, and paler faster. That is the only real difference between them, but it has consequences at the palette.

What it means when you mix

  • Titanium for value, zinc for temperature. When you need a colour a step lighter without losing its character, zinc gets you there with more paint and less bleaching. When you need a pale, high-key note or an opaque highlight, titanium does it in a knife-tip.
  • Chalkiness is a titanium symptom. Titanium tints go cool and dull as they lighten, because scattering overwhelms the colour. If your pale mixes look like they have flour in them, try zinc, or a titanium-zinc blend (many brands sell one), or lighten with a paler colour rather than white where you can.
  • Glazes and scumbles want zinc. Its transparency is a feature over a dry underlayer. Titanium covers.
  • Zinc and cracking. Zinc oxide films become brittle with age, and conservators have linked it to cracking and delamination, especially in thick layers or as a ground. Use it in upper layers and in moderation, and not as a priming.

How Halftint treats them

The engine knows the two whites as different paints with different tinting strengths, so a recipe that says three parts of white means three parts of the white you told it you own. If you have both, add both to your palette and it will choose. In practice it picks titanium for pale notes and reaches for zinc when a mix needs lightening without losing chroma, which is what a painter does by feel.