Characteristics of Common Blue Pigments

Home , Cobalt blue, Egyptian blue, Lightfastness, Maya blue

CAMEO: Conservation and Art Materials Encyclopedia Online at cameo.mfa.org

Pigment Composition CI numbers Usage Density Refractive Microscopic characteristics Other characteristics Health Index aniline blue triarylmethane dye CI 42780; patented in reacts with collagen to produce water soluble; used for inks toxic by ingestion Solvent Blue 3 January 1861 a blue-green fluorescence and for dying wool, nylon, leather, wood, and paper azurite natural basic copper Pigment Blue since antiquity 3.77- 1.730; strong birefringence; highly decomposes in acids chronic exposure carbonate, 2CuCO3- 30; CI 77420 3.80 1.838; refracting; particles are irregular evolving CO2; turns black may cause anemia Cu(OH)2 1.758 in size with fractured edges; with warm alkalis, hydrogen pleochroic from pale blue to sulfide or sulfur fumes deep blue blue verditer synthetic blue copper Pigment Blue European recipes 3.8 1.730; strong birefringence; highly decomposes in acids chronic exposure carbonate, 2CuCO3- 30; CI 77420 date to medieval 1.838; refracting; fine grain spheres evolving CO2; turns black may cause anemia Cu(OH)2 times 1.758 occur as aggregates; pleochroic with warm alkalis, hydrogen from pale blue to deep blue sulfide or sulfur fumes cerulean blue cobalt tin oxide, CoO-nSnO2 Pigment Blue developed in 1.78 - 1.84 very fine, rounded, isotropic, ASTM lightfastness=1 chronic inhalation 35; CI 77346; 1805, first sold in greenish-blue particles; no (excellent); Inert to acids may cause CI 77368 1860 birefringence; no pleochroism; and bases. asthma and appears deep red through possible fibrosis Chelsea filter chrysocolla copper silicate, CuSiO3- naturally 2.4 1.575, variable ground particles are appears green when ground no significant nH2O occurring blue 1.598, anisotropic with high as powder hazards mineral 1.597 birefringence, straight extinction and are pleochroic changing from pale green to colorless cobalt blue cobaltous aluminate, Pigment Blue developed in 3.83 1.662-1.74 irregular to rounded blue unaffected by acids, alkalis, skin contact may CoO.Al2O3 28; CI 77346 1802, sold as particles, no birefringence, no light and heat; ASTM cause allergies. artist pigment c. pleochroism; appears red lightfastness=1 (excellent) 1820 through Chelsea filter Egyptian blue double silicate of calcium Pigment Blue used by e =1.59, w irregular particle shapes; very stable; insoluble in no significant and copper, CaCuSi4O10 31; CI 77437 Egyptians; later =1.63 pleochroic from deep blue to acids; unaffected by light or hazards manufactured in colorless; strong birefringence; heat; ancient Egyptian blue Italy appears red with Chelsea filter may contain quartz and calcite as impurities indigo natural dye from Indigofera Natural Blue 1; natural indigo >1.662 fine, translucent dark blue, insoluble in water; no significant tinctoria, C16H10N2O2 CI 75780 used by 4th rounded particles that are discolored by reducing hazards (natural); century; weakly birefringent and appear agents & bleaches; ISO Pigment Blue synthetic dark red under Chelsea filter R105 Lightfastness 66; CI 73000 produced in Classification = 3-4 (synthetic) 1880. manganese BaMnO4-BaSO4 Pigment Blue discovered in 4.85 ~1.65 rectangular particles with ASTM lightfastness=1 toxic by inhalation blue 33; CI 77112 1907; marketed rounded edges; strongly (excellent) or ingestion as pigment in pleochroic from dark to pale 1935; production turquoise; strong birefringence discontinued in under crossed polars 1970s Maya blue palygorskite clay dyed with used in 1.522- fibrous or platy particles are unaffected by alkalis; indigo Mesoamerica 1.548 pleochroic (turquoise blue to soluble in hot concentrated since ancient yellow-green). Weak acids times birefringence under crossed polars. phthalocyanine copper phthalocyanine, Pigment Blue developed in 1.6 1.38 fine grain translucent to opaque slowly turns yellow then suspected blue C32H16N8Cu 15; CI 74160 1933; sold as particles with moderate to dissolves in concentrated carcinogen, paint pigment in strong birefringence; crystal sulfuric acid; ASTM teratogen 1935 type I appears deep red through lightfastness=2 (very good) Chelsea filter and crystal type II appears black

Pigment Composition CI numbers Usage Density Refractive Microscopic characteristics Other characteristics Health Index

Prussian blue ferric ferrocyanide, CI Pigment Blue developed in 1.83 1.56 cubic crystal system; isotropic; ASTM lightfastness=1 can emit hydrogen Fe4[Fe(CN)6]3 27; CI 77510 1704; first sold very fine particles (0.01 - 0.2 (excellent: but often varies cyanide gas if as artists' micrometers) appear black with manufacturer). Soluble exposed to acids, pigment c. 1730 under Chelsea filter in acids, decomposes in heat or UV alkali. radiation smalt ground potassium glass, K, 1.46-1.55 conchoidal fracture, with sharp lightfastness is variable; no significant Al, Co silicate edges and splinter; no poor covering power; hazards birefringence, no pleochroism; unaffected by acids, alkalis; transparent pale blue to deep may have quartz impurities purple particles ultramarine powdered lazurite Pigment blue extracted from 2.4 - about 1.5 irregular particles, no discolors when exposed to no significant blue, natural 29; CI 77007 lapis lazuli as 2.5 birefringence, no pleochroism, weak acids or sulfur fumes; hazards early as the 13th extinction under crossed polars; ASTM lightfastness=1 century naturally mixed with silicates, (excellent) calcite and pyrite ultramarine 3Na2O.3Al2O3.6SiO2.2Na2S Pigment Blue developed in 2.34 1.51; 1.63 small, round uniform particles, discolors when exposed to no significant blue, synthetic 29; CI 77007 1826, sold as no birefringence, no weak acids or sulfur fumes; hazards artist pigment in pleochroism, extinct in crossed ASTM lightfastness=1 1828 polars (excellent) vivianite ferrous phosphate, naturally 2.58- 1.60; lath-shaped crystals and slowly decomposes and Fe3(PO4)2 - 8H2O occurring mineral 2.68 1.63; 1.65 fragments with strong darkens in light and air used as pigment birefringence; appears blue- in 13th/14th c. green under Chelsea filter