Another way to detect changes in a brick wall is by comparing the color of the bricks. Because each generation of the handmade, clamp-fired bricks used by the Madisons at Montpelier were fired at slightly different temperatures, they exhibit very individualized ranges of colors.  Similarly, later machine-made bricks, such as the bricks used by the duPonts in ca. 1901, have a uniform red color and smooth texture that makes them easy to distinguish from the Madisons' handmade bricks.