PHYSICAL PROPERTIES OF PIGMENTS SPECIFIC GRAVITY 2 34 1.83 3.56 8-73 3.56 3-14 2.66 2.6 2.77 4.30 PARTICLE CHARACTERISTICS 8 min. flakes colloidal agg. vesicular vitr. frag, cryst. frag, crypt agg. angular frag, uneven, round, part, uneven spherulites cryst. frag, crypt, agg. ^ splintery, vitr. frag, small needles platy frag, min. round, gr. REFRACTIVE INDEX* an 2.4 ±, Tit' 3.02, fa 2.81 [LB] c 1.50 (isot.) [M*] «w 2.46, -YLi 2.61, fa 2.59 [LB] 2.42z,t- (w. bi.; pleo.) [M] (opaque) [M*] e 1.85 (var.) (isot.) [M] 1.87-2.17 (mostly 2.06) (isot.) [M*] e 1.553, w 1.544 [LB] «,«i.54[LB,M*] i.49-1.52 [M*] a, j8 (or w) 1.92,7 (or e) 2.01 (|| ext.) [M" « 1-539. ? 1-589.01-589 [LB] W 1.7-2.5 [M*] 3,10 prism, or ragged gr. mostly 1.8-2.0 (irr.) (bi.) [M*] PIGMENT NAME AND CHEMICAL COMPOSITION 1 Orpiment, As2S3 Prussian blue, Fe4[Fe(CN)6]s Pumice (volcanic glass), Na, K, Al, silicate Realgar, As2S2 Redlead,PbA(f95%) Sepia, organic Sienna, burnt, Fe203, clay, etc. Sienna, raw (goethite), FeA'H20, clay, etc. Silica (quartz), Si02 (chalcedony), Si02 Smalt, K, Co(Al), silicate (glass) Strontium yellow, SrCr04 Talc,3MgO-4Si02-H20 Titanium barium white, Ti02 (25%) + BaSa<75%) Titanium calcium white, TiC>2 (25%) + CaS04(75%) Titanium dioxide (anatase), TiOa (rutile), Ti02 Ultramarine blue (art.), (nat., lazurite), 3AlA-6SiOr2Na2S Ultramarine violet Umber, burnt, FeaOs + Mn02> clay, etc. Umber, raw, FeA-f MnQH-HA clay, etc. Van Dyke brown, bituminous earth Verdigris (copper basic acetate), Cu(C2HA)r2Cu(OH)2 Vermilion (art.), HgS (nat., cinnabar), HgS Viridian (chromium oxide, transparent), CrA-2H20 White lead (basic carbonate), 2PbCOrPb(OH)2 Zinc white (ordinary), ZnO (acicular), ZnO Zinc yellow, ZnCr04 1 Abbreviations: art. — artificial; med. = medium; nat. «• natural. The chemical formulas are those commonly acceptec in chemical and mineralogical literature, but they may not compare exactly with structural formulas based on x-ray diffrac 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 th< mineral pigments are chiefly from E, S. Larsen and H. Berman. 8 Symmetry terms (monoclinic, orthorhombic, etc.) are omitted because pigments are so finely divided that it is rare whei observations on crystal symmetry can be made. The term, *spherulitic, as used here means aggregates that tend towarc radial structure and spherical shape. 'Amorphous' describes materials that are microscopically formless but may be trul] crystalline on the basis of x-ray diffraction data. Abbreviations: agg. « aggregate(s); amorph. = amorphous; comp. = coni posite; crypt « cryptocrystallme; cryst. «* crystal(s); frag. - fragment(s); glob. » globule(s); sr. « grain (s); irr. « ir regular; mm. = minute; part. » particle(s); prism. - prismatic; round. « rounded; spher. = spheroidal; spheruL » spheru Imcjvar. sa variable; v. - very; vitr. — vitreous. 3-9 4.2 2-34 2.4 min. round, gr. round, or prism, gr, uniform small round, g! angular, broken frag. « and w 2.5 (w. bi.) [M*] €2.9, wi* 3"%* [M] «Li 3.146, «w 2.819 [LB] a,j9s 1.82, 73 2.12 [M*] 6.70 v. fine cryst. « 1.94, w 2.09 [M] 5.65 3-46 v. fine cryst. gr. spicules, fourlets min. spher. gr. € 2.O2, W 2.OO [M] £ 2.02, 0) 2.00 [M*] 1.84-1.9 (irr.; bi.) [M*] . t «,;: JO-----> * , »«*•*> v^vw — v,Aun*v,wvii, jtowt. — iauuuuu.j || — UitrftUCi; UlCU. = ^ ... _ , , \£ng 5 ^* f,^^* Th? lett?rs in Backets refer to the authorities for the refractive index data: M - H. E. Merwin M - H. E. Merwin, data by private communication, hitherto unpubHshed; W - C. D. West, data by private communica tion, hitherto unpubbhedj LB » E. S, Larsen and H, Berman; APL « A. P, Laurie and co-authors.