PHYSICAL PROPERTIES OF PIGMENTS

3.10	prism, or ragged gr.	mostly 1.8-2.0 (irr.) (bi.) [M*]
3.9	min. round, gr.	6 and w 2.5 (w. bi.) [M*]
4.2	round.orprism.gr.	€2.9,032.6 [M*]
2.34	uniform small round, gr.	n i.5i_green, i.63_red (isot.) [M]
2.4	angular, broken frag.	1.50 db (isot.) [LB]
pigment name and
chemical composition ^l
Orpiment, AsaSa
Prussian blue, Fe_4[Fe(CN)_6]3
Pumice (volcanic glass), Na, K, Al, silicate
Realgar, AsaS_2
Red lead, Pb_30_4 (c 95%)
Sepia, organic
Sienna, burnt, FejOa, clay, etc.
Sienna, raw (goethite^FeaOs-HsO, clay, etc.
Silica (quartz), SiOa
(chalcedony), Si0_2
Smalt, K, Co(Al), silicate (glass)
Strontium yellow, SrCrO*
Talc,3MgO-4Si02-H_20
Titanium barium white, Ti02 (25%)
+ BaSO<(_75%)
Titanium calcium white, TiC^ (25%)
Titanium dioxide (anatase), TiO
(rutile), Ti0_2
Ultramarine blue (art.), I
(nat, lazurite), 3Na_20--
3Al_20_3-6Si0_2-2Na_2S
Ultramarine violet
Umber, burnt, FeA + MnOa, clay, etc.
Umber, raw, FeA+Mn0_2+H_20, clay, etc.
Van Dyke brown, bituminous earth
Verdigris (copper basic acetate),
Cu(C2HAV2Cu(OH)_2
Vermilion (art.), HgS
(nat, cinnabar), HgS
Viridian (chromium oxide, transparent),
CrA-2H_20
White lead (basic carbonate),
2PbC0_3-Pb(OH)_2
Zinc white (ordinary), ZnO
(acicular), ZnO
Zinc yellow, ZnCA

specific	particle
gravity ^a       characteristics ^8
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.
round, gr. (blue, rose,
3.64
3.20
1.66
and violet)
uneven, round, gr.
uneven, round, gr.
irr. amorph. part,
cryst. frag.
8.09
8.1
3-3*
6.70
5-65
3.46
hexagonal gr. and
prisms
cryst. frag,
spherul. gr.
v. fine cryst.
v. fine cryst. gr.
spicules, fourlets
min. spher. gr.

refractive index*
au 2.4 ±, 7« 3.02, fa,- 2.81 [LB]
c 1.50 (isot.) [M*]
olu 2.46,7Li 2.61, fa,- 2.59 [LB]
2.42w (w. bi.; pleo.) [M]
(opaque) [M*]
c 1.85 (var.) (isot.) [M]
1.87-2.17 (mostly 2.06) (isot.) [M*]
e 1.553, « 1.544 [LB]
e,o)l.54[LB, M*]
1.49-1.52 [M*]
a, /5 (or «) 1.92, 7 (or e) 2,01 (|| ext.) [M*]
«i-539>T 1.589,01.589^6]
n^c 1.7-2.5 [M*]
c 1.56 (isot.) [M*]
mostly 2.2-2.3
mostly 1.87-2.17 [M*]
1.62-1.69 [^M*l
a 1.53,7 1-56 [M]
, wl< 2.819 [LB]
a, /3_S 1.82, 73 2.12 [M*]
« 1.94, w 2.09 [M]
€ 2.02, OJ 2.00 [M]
€ 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 accepted
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 the
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 when
observations on crystal symmetry can be made. The term, *spherulitic, as used here means aggregates that tend toward
radial structure and spherical shape. 'Amorphous' describes materials that are microscopically formless but may be truly
«H*»*«1tJ_w./«, *t. 1—:5~f	 j:iL. —•— J-^- alt...—-^	 	 /.\ T, ^J	,	^J	^J
uac; var. « vaname; y. — very; vitr. *= vitreous.
^4 Unless otherwise indicated, all refractive index measurements are by sodium light. S is the symbol used by H. E. Merwin
to indicate greater or less indefiniteness or irregularity in the case of aggregates, especially in respect to refractive index.
Abbreviations: bi. « birefringent; c —circa; ext = extinction; isot. « isotropic: |} « parallel; pleo. « pleochroic; s.^
strongly; w. « weakly. The letters in brackets refer to the authorities for the refractive index data: M * H. E. Merwin;
M* «= H. E. Merwin, data by private communication, hitherto unpublished; W « C. D. West, data by private communica-
tion, hitherto unpublished; LB » E. S. Larsen and H. Berman; APL « A. P. Laurie and co-authors.