Permanence of Watercolour Pigments

By JOHN TOFT

MODERN WATERCOLOURS are much more permanent than they used to be. The best manufacturers have removed unstable colours from their range, replacing them with more permanent pigments.

Winsor & Newton’s leaflet, Perfecting the Fine Art of Water Colours, contains a wealth of information on all aspects of watercolour pigments. You should be able to pick up a copy from your local art supplies shop.

Included in the leaflet is a Composition & Permanence Table which gives the Colour Index of each pigment, e.g. Cobalt Blue is Pigment Blue 28, abbreviated to PB 28. This is useful as different manufacturers may give the same pigment different names. For example, the colour Winsor & Newton calls Brown Madder (PR 206) is called Avignon Orange by Maimeri.

The table also rates each colour in the W & N range for permanence, defined as “its durability when laid with a brush on paper displayed under a glass frame in a dry room freely exposed to ordinary daylight and an ordinary atmosphere”. Pigments are rated AA (extremely permanent), A (permanent), B (moderately durable) and C (fugitive).

Only 3 colours in W & N’s Artists’ Water Colour range are rated B. These are Alizarin Crimson, for which Permanent Alizarin Crimson is a permanent alternative, Rose Madder Genuine and Opera Rose.
Permanent Rose is the nearest permanent alternative for the last two. No colours are rated C.

The Cadmiums are all rated A(ii), permanent, but cannot be relied upon to withstand damp. French Ultramarine, Ultramarine (Green Shade), Ultramarine Violet and Aureolin are rated A(iii), permanent,
but bleached by acids and acidic atmosphere. Also, Aureolin is ‘A’ rated in full strength but may fade in thin washes. Antwerp Blue and Prussian Blue are rated A(iv), “fluctuating colour, fades in light, recovers in dark”. If these last two colours have faded in a painting and it is put in a dark place (under a bed for example) the colour will regain its intensity.

The table also gives the ASTM rating for colours which have been tested by the American Society for Testing and Materials.

The ASTM has set standards for the permanence of art materials, including a colour’s lightfastness. Each colour tested is rated from I-V according to its resistance to fading. In this system, I and II are considered permanent for artists’ use.

Provided watercolours are painted on acid free paper using permanent pigments and are properly framed using acid free mats and backing boards, then they can be displayed without fear of deterioration. Colour fading in older paintings is the result of the use of impermanent pigments. Modern colours can be used with confidence. As Winsor & Newton puts it “The quest for permanence has turned water colour from a less lightfast, delicate medium into one which is equal to oil colour despite the extreme dilution of the paint film".



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