About the chemical structure:
Cadmium yellow: cadmium sulfide (CdS)
Cadmium orange/red: cadmium sulfide (CdS) + cadmium selenide (CdSe) in varying proportion
|Formula:||CdS (yellow); CdS + CdSe (orange/red)|
|Crystal system:||greenockite: Hexagonal - Dihexagonal Pyramidal (at Mineralogy Database)|
|Refractive index:||e=2.506, w=2.529|
|Color Index (C.I.)||PY 35 (yellow); PR 108 (red)|
How can you identify Cadmium yellow/red?
IRFC: white (c. yellow) / orange yellow (c.red) / yellow (c. orange)
OM: The particle sizes of the deeper cadmiums are about fifty times larger than the paler varieties. They are transparent particles that appear in clusters, microscopically.
Microscopic appearance at x500 mag
It's identified by means of FTIR and Raman. Cadmium pigments are dissolved in hydrochloric acid and nitric acids and are unchanged by sodium sulfide
Raman spectra: University College London;
FTIR spectra: IRUG;
Usage and handling:
Degradation processes: it does discolour however upon combined exposure to the light, water and CO2 forming cadmium carbonate. For that reason it can not be used in mural painting techniques. Pigment used on the damp wall will change. Pigment exposed to the same amount of light used on canvas or panel will not change. Cadmium pigments are classified as absolutely permanent with the exception that they are not suitable for the exterior applications and for mural painting techniques. also cadmium pigments tend to blacken when mixed with copper pigments.
non toxic. Cadmium yellow/red pigment is not considered to be toxic, but care should be used in handling the dry powder pigment to avoid inhaling the dust or ingesting the pigment in any form. It considered to be carcinogenic in some countries.
Artists Pigments. A Handbook of Their History and Characteristics, Vol. 1, L. Feller, Hrsg., Cambridge University Press, London 1986, p. 65 -108.