Editing Ultramarine (section)

== Visual properties ==
[[File:Natural ultramarine painted.jpg|thumb|Natural ultramarine painted]]

The best samples of ultramarine are a uniform deep blue while other specimens are of paler color.<ref>{{Cite journal |last=Roy |first=Ashok |title=Artists' Pigments: A Handbook of Their History and Characteristics |url=https://www.nga.gov/content/dam/ngaweb/research/publications/pdfs/artists-pigments-vol2.pdf |journal=National Gallery of Art |volume=2 |pages=38}}</ref>

Particle size distribution has been found to vary among samples of ultramarine from various workshops. Numerous grinding techniques used by painters have resulted in different pigment/medium ratios and particle size distributions. The grinding and purification process results in pigment with particles of various geometries. Different grades of pigment may have been used for different areas in a painting, a characteristic that is sometimes used in art authentication.<ref>{{Cite journal |last=Boer |first=J. R. J. Van Asperen De |date=1974 |title=An Examination of Particle Size Distributions of Azurite and Natural Ultramarine in Some Early Netherlandish Paintings |url=https://www.jstor.org/stable/1505730 |journal=Studies in Conservation |volume=19 |issue=4 |pages=233–243 |doi=10.2307/1505730 |jstor=1505730 |issn=0039-3630}}</ref>