Natural yellow chalk in traditional old master drawings

Beginning in the late 15th century, European artists added natural yellow chalk to their limited selection of natural chalks by sawing cohesive pieces of raw unprocessed yellow ocher into drawing sticks. This paper examines the history, geology, chemical composition, sources, production, and physical characteristics of natural yellow chalk as a traditional old master drawing material. Chalk nomenclature is presented to clarify the relationship of natural yellow chalk with respect to fabricated yellow chalks, including synthetic yellow chalks and artificial yellow chalks. Raw unprocessed specimens of natural yellow chalk from France and Germany were obtained and studied using optical microscopy and field emission scanning electron microscopy to observe their appearance, particle structure, and working properties when used as a drawing material. Their chemical composition was determined using x-ray diffraction (XRD) analysis and scanning electron microscopy with energy dispersive x-ray spectroscopic (SEM-EDX) microanalysis. These results were compared with the physical characteristics and chemical composition of traditionally used natural yellow chalk documented in the historical record.