Translucent Pigments and Opaque Pigments in Art

Artists will soon discover that some art pigments have better covering power than others; titanium white will mask most pencil lines, whereas French ultramarine will dry translucent. Why do some art pigments have better covering power than others?

Opaque Pigments in Oils and Acrylics

Paint is a suspension of tiny colored particles (or powder) within a medium, which might be polymer, oil or alkyd. Different pigments will have particles of different sizes and this will determine how much medium will be needed to make the paint flow. The power of a chosen pigment to cover what is beneath is determined by several factors, namely being:

The size of the pigment particles.
The thickness of the paint layer.
The amount of medium used with the paint.
The refraction indices of the pigment (explained next)

Opaque Pigments in Art

Pigments that have high opacity comprise of ground powder that causes light to scatter in different directions. It is the scattered light rather than the pigment particles themselves that causes opacity. Looking through a microscope, the pigment will appear transparent. This is because they are suspended in a highly-refractive medium.

Substances (or pigment powder) that have a high ability to bend light in different directions (or to scatter light) have high refractive indices (or RI). High refractive indices equal high opacity.

Oil Pigments for Glazing Techniques

The tendency for some pigments to dry translucent than when it was wet is called pentimento. Earlier alterations to a painting can be seen beneath a final layer of paint, particularly in early 20th century art. This is due to the transparent nature of the final layer of paint.

Translucent pigments exhibit a different behavior to opaque pigments when mixed with other colors or applied in art. A transparent pigment applied onto a white ground will appear brilliant, because some of the white surface beneath reflects the light back. If the same pigment were applied onto a dark or black background, most of the light would be absorbed, causing the color to appear dull. For this reason, translucent pigments are ideal for glazing techniques, as the color beneath is still visible.


Opaque Pigments in Painting

Pigments that have high (or medium) covering power include: lemon yellow, cadmium yellow, chrome yellow, Naples yellow, yellow ochre, light red, cadmium orange, cadmium red, scarlet lake, cerulean blue, cobalt blue, chrome green, Indian red, burnt umber, Vandyke brown, Payne’s grey, ivory black, lamp black and titanium white. These colors can be used for flat, even coverage and if glazing, will require some additional linseed oil (or applicable medium) to make the color transparent.

Translucent Pigments for Painting

Pigments that are more translucent in nature are: permanent rose, permanent crimson, alizarin crimson, dioxazine blue, ultramarine, pthalo blue, Prussian blue, viridian green, terre verte, sap green, burnt sienna, raw sienna and raw umber. These colors, being transparent in nature will need careful selection of an opaque color to provide body and covering power if this is needed.

Mixing Transparent Hues with White

Beware that mixing a translucent color with titanium white (which has high RI) will not bring a paler version of the hue. Apply a thin glaze of ultramarine on a white surface, and a brilliant blue will result. Similarly, apply a thin glaze of permanent rose on a white surface and a brilliant pink will be the outcome. Mix ultramarine with white, and an opaque, rather grayish, flat blue will come back. Mix permanent rose with white, and a candy-floss pink will be the consequence. Translucent pigments are ideal for glazing techniques, but careful mixing is required if an opaque paint layer is needed.

Oil Pigments for Glazing or Impasto

A selection of translucent, semi-translucent and opaque paints will come in useful for the artist. Translucent colors are ideal for glazing techniques and for deepening a color beneath. Opaque colors will come in useful for alla prima, impasto or simply to cover up unwanted marks. Opaque colors will also provide a flat, even paint layer if this is desired.
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