Why Paint and Pigments Degrade

Still Life: Vase with Fourteen Sunflowers 
by Vincent van Gogh (1888).
The left hand side of the image simulates
the appearance of van Gogh's painting 129
years ago, before the yellows darkened.
 Note: This work is in the Public Domain
PD-1923

By Jim Hingst  

Paint and pigment selection is extremely important for the serious artists because the colors used in the works of art are subject to degradation. Some of the great works of artists, such as Vincent van Gogh, are either fading, flaking, cracking, chalking or darkening. 

Many of the paints, which have suffered the most degradation, are comprised of synthetic pigments created in the mid-nineteenth century. The brilliant chrome and cadmium colors, which were so popular during the period of the Impressionists, Post-Impressionists and Fauvists, are not lasting much longer than the artists, who painted them.

To ensure that your paintings do not suffer the same fate, you need to carefully select your paints and pigments. While Father Time may play some role in how paint ages, other factors are more significant in the degradation process. These factors include temperature, humidity, oxygen, carbon dioxide, sulfur dioxide and light, both visible and ultraviolet. Degradation of color also occurs when one pigment chemically reacts with another.

Both visible and ultraviolet light have enough energy to initiate chemical reactions that affect pigments and the binding medium of paint. Exposure to ultraviolet light can cause a variety of undesirable results. The resin is especially vulnerable. It can become brittle and crack. It binding ability can degrade loosening its bond to the pigment particles. This can develop into chalking in which loose pigment is left on the surface of the paint after the binder has wasted away.

Light also affects pigments. The pigment particles absorb light and convert it into heat. This heat can cause a chemical change in the pigment. In this chemical reaction the pigment molecule can actually either gain or lose electrons, which results in a color change. Colors can fade, yellow or darken. Inorganic pigments are generally much less susceptible to photo degradation than organic pigments. You should take this into consideration as you select either paints or pigments. 

Paint fillers, which manufacturers often included in their formulations to lower their raw material cost, have, in many cases, compounded the problem of discoloration. In the age when artists  ground their own pigments and made their own paint, it usually consisted of just  pigment and a resin, such as linseed oil. The old masters usually did not add filler into their paint to extend coverage and lower their costs. There are a few paint manufacturers, who still make paint the old fashioned way without additives. 

Other mechanisms of degradation, such as oxidation, change the chemistry of the painted image. These chemical changes can alter the color of the paintings as well as weaken the surface of the paint, resulting in flaking.

Material selection is one way to minimize degradation. Varnishing, which was practiced by the old masters, can also provide protection by forming a barrier between the atmosphere and the paint. These old timers must have been doing something right. The paintings of the Renaissance have lasted for hundreds of years. That leads me to believe that we should revive some of these old practices.

In summary, the follow factors can effect degradation of paints and pigments:

● Ultraviolet light can degrade both the pigment and the resin binder.

● Temperature, humidity, oxidation, carbon dioxide and sulfur dioxide contribute to the degradation process.

● Chemical reactions between two different pigments can affect changes in color.

● Paint fillers can also contribute to problems of discoloration.

See my article Buying Artist's Oil Paints.

About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 450 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.  Vinyl Sign Techniques is available at sign supply distributors and at Amazon. 

Slides of Jim's Artwork

© 2017 Jim Hingst