Old paintings turn yellow primarily due to the aging and chemical changes of the varnish and the paint itself.
The Varnish's Role in Yellowing
Aging Varnish
A key contributor to yellowing is the varnish applied to the painting's surface. Over time, this varnish undergoes chemical changes, leading to a yellow hue.
Cleaning and Residue
- Dutch researchers have found that when old-master paintings are cleaned, larger molecules of aged varnish can be left behind.
- These remaining molecules contribute to the yellowing of canvases and panels, according to research.
- Therefore, the cleaning process, while intended to restore a painting, can also inadvertently intensify the yellowing effect.
The Paint's Contribution
Oil-Based Paints
Oil-based paints, often used in older paintings, can also yellow with age. This yellowing occurs due to the natural oxidation of the oils in the paint.
Pigment Interactions
Some pigments can interact with the binder (usually oil) over time, also contributing to the yellowing effect.
Summary
Here’s a table summarizing the key factors:
| Factor | Description |
|---|---|
| Aged Varnish | Varnish undergoes chemical changes, leading to a yellow color. |
| Cleaning Residue | Left-behind varnish molecules during cleaning intensify the yellowing effect. |
| Oxidation of Oils | The oils in oil-based paints oxidize over time, leading to a yellow color. |
| Pigment Interactions | Some pigments interact with the binding medium causing a color change. |
Practical Implications
- Understanding the reasons behind yellowing is crucial for art conservators.
- New conservation techniques aim to minimize the yellowing caused by both varnish and paint.
- Museums invest in research to best preserve old paintings, often considering the impact of varnish removal.
