The Zinc White Debate (and why we’re keeping it in our oil ranges)

Zinc White (PW4) is a cool, semi-transparent white pigment composed of zinc oxide which has been used in artist paints since the 18th century. It is commonly found in paints labeled as Mixing White and Transparent White, and is also often added to Titanium White (PW6) to improve its handling qualities. Recently there has been much discussion about Zinc White’s suitability for use as a pigment in oil paint, with concerns that zinc oxide causes a brittle paint film that can crack and delaminate.

In this article, we explain the pros and cons of Zinc White and answer some frequently asked questions about its use in our own Professional and Artist oil paint ranges, including best practice when painting with it.
 

Text provided by Paul, a member of our technical team

It certainly appears that the Zinc White question is heating up; with lead duly buried and cadmium put at ease, it looks like there’s a new bad guy in town.

It’s fair to say the issue is not a new one. Zinc White has been used in artist paints for 250 years and is still in wide use today. As with many pigments, it comes with its own characteristics — some good and some bad.
 

What are the concerns about Zinc White?

The concerns around Zinc White were well documented, even back in the early days of its use in oil paint. It’s clear that zinc oxide reduces the flexibility of paint, and less flexibility means a higher risk of cracking when stressed. This brittleness develops over time and is not usually obvious within the early months of a painting’s life. It starts to become apparent thereafter when compared to non-zinc oxide pigments. On this point, you should keep in mind that linseed oil also continues to lose flexibility as it ages, with any given painting having more flexibility at 50 years than it will at 150 years. Unfortunately, the reduced flexibility seen with Zinc White is not yet fully understood and continues to be investigated.

Paints containing Zinc White do not consistently create a problem. In most cases, the degree of flexibility is still sufficient for a well-supported painting. After all, Zinc White has been well utilised in mixing whites for a long time so we may assume that a large majority of paintings out there will contain some amount, yet we don’t see wide-scale cracking or delamination.

That leaves us with trying to understand if we have a problem or not, and what real advice we can give.

 

What are the advantages of Zinc White?

• It offers a very clean, cool white compared to other white pigments.
• It offers a more transparent white, that makes it more gentle and subtle in mixes.
• It reduces the yellowing and improves handling of other white pigments, including Titianium White. It is, in fact, often added to Titanium White oil paint for this reason.
• It improves lightfastness.
• It has a long open time.
• It suppresses mildew formation on the paint film.
• It is unique. There are no other cool white pigments with the same properties as Zinc White.

Below is a comparison using paints in our Professional and Artist oil range. Small amounts of Titanium White and Zinc White were added to Alizarin Crimson, Burnt Sienna and Ultramarine Blue to see their comparative effects in mixtures:

Titanium White has a very high tinting strength, and just a small amount increases the opacity of the colour and gives it a pastel effect. Many artists find it’s covering power useful, but it can be overwhelming as a mixing white.
 

Zinc White is more subtle than Titanium White. More is needed to have a significant effect on the colour, and it tints the mixture without adding opacity or chalkiness.
 

Do Jackson’s oil paints contain Zinc White?

Some do. The pigments used are stated on the label of all of our paints. Zinc White can be identified by the pigment index number PW4.
 

How much Zinc White do they contain?

This varies for each colour. Our paints each have their own uniquely balanced formulas, the ingredients of which may each play a part in its flexibility. Pigment to oil ratio, oil types, co-pigments and enabling ingredients will all play a part.
 

Why do you include Zinc White in your Titanium White oil paint?

Used alone, titanium dioxide (known as Titanium White, pigment index number PW6) makes a long, stringy paint which remains relatively soft when dry. Adding Zinc White improves these qualities and, as stated above, improves lightfastness and non-yellowing properties.
 

Do these concerns affect Zinc White watercolour and acrylic paints?

No, there is no evidence that Zinc White causes cracking or delamination in acrylic or watercolour.
 

Will oil paints which contain Zinc White crack or delaminate?

Oil paints containing Zinc White will be more brittle than those that don’t. However, there are many variables involved including what the paint is mixed with, how it is applied, how it dries, and what it’s exposed to during its life.

We formulate our Artist and Professional oil paints to be sympathetic towards flexibility, and we have taken a look at older samples of our zinc-containing paints. Whilst less flexible, we cannot see any dramatic failures in the aged dry film. We therefore feel that the formulation aspects present a sound basis for zinc white paint and, provided the paint is used with good practice, should not produce any significant concerns.
 

What is best practice when using Zinc White in oil painting?

• Avoid use in underpaintings or lower layers.
• Do not apply thick, heavy layers. keep as thin a layer as needed.
• Avoid adding white spirits or solvents.
• Use of additional oil, especially linseed stand oil, is believed to be beneficial.
• Use sturdy supports and avoid stretching, bending, or flexing.
• Minimise transportation or shipping of the finished painting, package well with supportive transport frames and supports. Label clearly as ‘fragile’.
• Keep the painting in a moderate environment as possible, ideally 16-25°C and 40-60% relative humidity. Avoid heavy/sudden swings in temperature.

The last three points are good practice for any oil painting, not just those which use Zinc White.

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Oil paints on jacksonsart.com:

• Jackson’s Professional Oil
• Jackson’s Artist Oil

 

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Further Reading:

• Cadmium in Crisis
• Gamblin Oil Colour: Choosing from Their Many Whites
• What is Dark Yellowing?