An icy white, a semi-translucent white, what was once thought of as a great solution to work around lead white may actually cause cracking and early embrittlement in oil paint. Zinc Oxide seems to be safe for other media though. For example, zinc appears to be fine in watercolor, that is, if you even use white in watercolor.
Once upon a time, we actually sold off a bunch of expensive oil colors on ebay because they contained zinc. There's been no looking back. Theoretically it could be possibly that a helpful amount of zinc in oil paints could exist (it's complicated), but it might be years before we know how much zinc is beneficial and how much will cause early embrittlement of a painting.
This color has been the subject of a lot of controversy in oils due to its role in cracking.
Zinc Oxide is sometimes described as a crisp, cool white, though this may not always be the case. Back when we used to use it, we favored the bluer versions of zinc for mixes with cyans to make blue tints. However some of the blue pigments may be negatively affected in tints of pure zinc oxide (see Golden’s research on mixing whites.
Many convenience colors contained a bit of zinc white to soften the overall look, and some brands have reformulated their paints to remove PW4. It is hard to replace it entirely, and so certain blends cannot be perfectly recreated. Zinc was celebrated for its role in emulating some of the gentle, gauzy transparency of lead white without the lead-- though, shocker, zinc might actually contain lead sometimes (see below). Zinc's note of translucency is prized in many forms of realistic painting or to make atmospheric effects in abstract painting.
Zinc is a very slow drier.
In some cases, a brand's basic Titanium White contained a hearty dose of zinc as a matter of course because it imparted desirable working properties to the Titanium. Some brands may not actually be disclosing on the tube whether there is PW4 (unlisted) in their Titanium White, and in general disagreement about zinc white seems to be the rule (for reference, we noticed this discussion.
However, it is now widely recognized that too much zinc can be linked to early embrittlement and delamination. A name that comes up frequently in zinc research is Marion Mecklenburg. In 2018, Golden undertook research on zinc and embrittlement. They published a series of articles on their research:
Zinc Oxide Warnings, Cautions, and Best Practices,
Zinc Oxide Reviewing the Research
Zinc Oxide Search for the Dividing Line, and also there is
Natural Pigments Zinc Free Zone
As mentioned earlier, as an additional caution, Zinc white PW4 sometimes contains lead-- see Monona Rossol's work for more information. This explains why some dry pigment is marked "zinc white - lead free". For more information on the hazards associated with zinc pigments, see Monona Rossol's book, The Artist's Guide to Health and Safety.
Please note there are different ways in which zinc was prepared. Long ago, there used to be a version with a larger particle size.
