PHYSICAL .fKUJPJiKllJiS Ufc PIGMENT NAME AND CHEMICAL COMPOSITION x Orpiment, As2Ss Prussian blue, Fe4[Fe(CN)Q]s Pumice (volcanic glass), Na, K, Al, silicate Realgar, As2S2 Red lead, Pb304 0:95%) Sepia, organic Sienna, burnt, Fe2Os, clay, etc. Sienna, raw (goethite), Fe203-H20, clay, etc. Silica (quartz), Si02 (chalcedony), Si02 Smalt, K, Co(Al), silicate (glass) Strontium yellow, SrCrO4 Titanium bariurn white, TiOa (25%) -f-BaS04(75%) Titanium calcium white, Ti02 (25%) -fCaS04(75%) Titanium dioxide (anatase), Ti02 (rutile), Ti02 Ultramarine blue (art.), (nat., lazurite), SPECIFIC PARTICLE GRAVITY 2 CHARACTERISTICS s 3.4 min. flakes 1.83 colloidal agg. — vesicular vitr. frag. 3.56 cryst. frag. 8.73 crypt, agg. — angular frag. 3.56 uneven, round, part. 3.14 uneven spherulites 2.66 cryst. frag. 2.6 crypt, agg. — splintery, vitr. frag. — small needles 2.77 platy frag. 4.30 min. round, gr. REFRACTIVE INDEX* dLi 2.4 =J=, TLf 3.02, fai 2.81 [LB] Ultramarine violet Umber, burnt, Fe203 -f Mn02, clay, etc. Umber, raw, Fe2034-Mn02-f H2O, clay, etc. Van Dyke brown, bituminous earth Verdigris (copper basic acetate), Cu(C2H302)raCu(OH)2 Vermilion (art.), HgS (nat., cinnabar), HgS Viridian (chromium oxide, transparent), Cr2i.54[LB,M*] 1.49-1.52 [M*] a,/3 (or w) 1.92,7 (or €) 2.01 (|| ext.) [] a 1-539*7 i-589>0 i.] n^c 1.7-2.5 [M*] 3.10 prism, or ragged gr. mostly 1.8-2.0 (irr.) (bi.) [M*] 3.9 min. round, gr. 4.2 round, or prism, gr. 2.34 uniform small round, gr, 2.4 angular, broken frag. — round, gr. (blue, rose, and violet) 3.64 uneven, round, gr. 3.20 uneven, round, gr. 1.66 irr. amorph. part. — cryst. frag. 8.09 hexagonal gr. and prisms 8.1 cryst. frag. 3.32 spherul. gr. 6.70 v. fine cryst. 5.65 v. fine cryst. gr. — spicules, fourlets 3.46 min. spher. gr. £ and co 2.5 (w. bi.) [M*] €2.9, «2.6[M*] 1.50 ± (isot.) [LB] c 1.56 (isot.) [M*] mostly 2.2-2.3 [M*] mostly 1.87-2.17 [M*] 1.62-1.69 [M*] a 1.53, 7 1.56 [M] .8i [M] 6^3.1 €^3.146, a, fa 1.82, 73 2.12 [M*] € 1.94, w 2.09 [M] € 2.02, W 2.00 [M] 6 2.02, W 2.00 [M*] 1.84-1.9 (irr.; bi.) [M*] 1 Abbreviations: art. = artificial; med. = medium; nat. — natural. The chemical formulas are those commonly acce in chemical and mineralogical literature, but they may not compare exactly with structural formulas based on x-ray di£ tion data or even on critical chemical analysis. 2 The figures for specific gravity of the artificial pigments are mainly from H. A. Gardner, pp. 710-712, and those on mineral pigments are chiefly from E. S. Larsen and H. Berman. 8 Symmetry terms (rnonoclinic, orthorhombic, etc.) are omitted because pigments are so finely divided that it is rare ? observations on crystal symmetry can be made. The term,' spherulitic, as used here means aggregates that tend toi radial structure and spherical shape. 'Amorphous* describes materials that are microscopically formless but may be 1 crystalline on the basis of x-ray_diffraction data. Abbreviations: agg. =» ageregate(s); amorph. = amorphous; comp. = < posite; crypt. « cryptocrystalline; cryst. = crystals); frag. «• fragmentfs); glob. — globule(s); gr. «• grain (s); irr. • regular; min, » minute; part. =• particle(s); prism. = prismatic; round. = rounded; spher. = spheroidal; spherul. = spl liticjvar. ~ variable; y. — very; vitr. = vitreous. 4 Unless otherwise indicated, all refractive index measurements are by sodium light. S is the symbol used by H. E, Me to indicate greater ox less indefiniteness or irregularity in the case of aggregates, especially in respect to refractive ii Abbreviations: bi, = birefringent; c = circa; ext. = extinction; isot « isotropic; |] - parallel; pleo. -= pleochroic; stronglp w. sa weakly. The letters in brackets refer to the authorities for the refractive index data; M = H. E. Mei M* « H. E. Merwin, data by private communication, hitherto unpublished; W — C. D. West, data by private commu tion, hitherto unpublished; LB « E. S. Larsen and H. Berman; APL « A. P. Laurie and co-authors.