Chromium, derived from the Greek word “chroma” meaning “color,” has been a central element in the development of pigments due to its vivid and strong colors. This lesson explores the historical and scientific significance of chromium in pigments, examining its characteristics, spectra, and usage from the 19th century to modern times.
Objectives:
- Analyze the spectral features of chromium in its pure form and in various pigments.
- Explore the historical timeline and applications of chromium-based pigments in art.
- Compare the spectral behavior of chromium in different compounds, including historical and modern pigments.
Materials:
- Pure chromium sample.
- Pigments containing chromium, including chrome yellow, viridian, chrome oxide green, cobalt chromite blue, strontium yellow, and chrome titanate orange from Pigments Checker Standard and Modern Art.
- XRF spectrometer with low keV filter setup.
Lesson Plan:
1. Introduction to Chromium in Pigments
- Present chromium’s position in the periodic table (atomic number 24) and its spectral lines (Kα at 5.4 keV and Kβ at 5.9 keV).
- Examine a cube of pure chromium to observe the spectrum, emphasizing the strong Kα peak (~150,000 counts) under low keV setup.
3. Historical Pigments Containing Chromium
- Introduce the Pigments Checker timeline to contextualize the development of chromium pigments.
- Analyze spectra of chrome yellow (lead chromate, commercialized in 1816), highlighting the lower count (~2,000 counts) due to lead’s X-ray absorption.
- Compare this to chrome oxide pigments, such as viridian (1838) and chrome oxide green (1862), emphasizing stronger chromium peaks due its higher chromium concentration.
- Explore cobalt chromite blue (1935)
- Discuss modern pigments like strontium chromate (strontium yellow) and chrome titanate orange.
