The visual differences between linseed oil and commercial alkyd paints are quantified by colorimetry and spectrophotometry. Photo: Emile Askey

Project Objectives
This focused, lab based project—a collaboration between the Science and Field Projects departments of the GCI—seeks to improve understanding of the visual differences between surfaces painted with different types of paint materials. The project specifically focuses on comparing the appearance of historic architectural paints with replication paints, although the same research may also be applied to other contexts, such as painted sculpture.

This first phase of research addresses linseed oil paints compared to alkyd house paints.

The project objectives are:

• to develop a methodology for measuring visual differences between historic architectural paints and commercial paints commonly used for their replacement;
• to adapt common methodologies for measuring visual differences of painted surfaces in general to historic restoration goals;
• to measure the appearance differences in these paint systems with different types of illumination (metamerism); and
• to determine the primary cause of inconsistency of appearance between the two paint types.

	Paints were made by hand with historically appropriate materials. Photo: Cassie Myers

Project Overview
The substitution of historic paints with modern paints often results in visual changes that extend beyond color. Visual qualities—such as texture, transparence, and the shift in color in different types of light, known as metamerism—contribute to the appearance of replicated paints in historic interiors, often with significant impact. However, these differences in appearance have not been well represented in the commercial paint industry or understood in the conservation field. Moreover, with the choice of paint driven by cost, needs for durability, and other practical requirements, commercial paints often do not represent the nuances and impact of appearance.

In order to gain a better understanding of differences in paint appearance, this project compares the visual properties of historic linseed oil paints with color matched alkyd commercial paints. The research uses primarily spectrophotometry and colorimetry to analyze differences.

The methodology for measuring such differences may be applied to other contexts and problems, such as painted outdoor sculpture.

Project activities are broken down into four components, and include:

• documentary research on architectural paint replication research (Component 1);
• survey among paint analysts and conservators to determine need for research (Component 2);
• modification of research program to visually compare historic paints with commercial paints (Component 3); and
• routine dissemination of research in the conservation field (Component 4).

Last updated: March 2009