PAINT PIGMENTS AND THEIR PROPERTIES
For the student of paint technology, who is not already acquainted with
the chemistry and physics of the various raw pigments which are largely
used in the manufacture of paints, the writer advises a careful reading
of this chapter, in which the matter has been condensed as much as
possible. In order to more thoroughly acquaint the reader with the
physical constitution of the pigments under consideration, there has
been included photomicrographs, which show to advantage the structure of
each.[15]
[15] The author gratefully acknowledges the assistance of Dr. J. A.
Schaeffer in the preparation of the photomicrographs shown in
this chapter.
[Illustration: By Polarized Light
By Transmitted Light
Basic Carbonate-White Lead]
=Basic Carbonate-White Lead.= This pigment is made by stacking clay pots
containing dilute acetic acid and lead buckles, in tiers, and covering
them with tan bark. Fermentation of the tan bark, with subsequent
formation of carbon dioxide acting on the acetate of lead formed within
the pots, produces basic carbonate of lead. After complete corrosion,
the white lead is ground, floated, and dried. Corroded white lead has a
specific gravity of 6.8 and contains about 85% lead oxide and 15% of
carbon dioxide and water. Its opaque nature and excellent body renders
it extremely valuable as a constituent of paints. Checking and chalking
progress rapidly when the pigment is used alone. The various sized
particles, both large and small, resulting from the corrosion process,
are prominently shown in the photomicrograph.
[Illustration: Crystals of Cerussite in Old Dutch Process White Lead.
(Greatly magnified)]
[Illustration: White Lead (Quick Process)]
On account of its alkaline nature, this pigment acts upon the
saponifiable oil in which it is ground, forming lead soaps which
accelerate chalking of white lead--the greatest evil attending its use.
Solubility in carbonic acid of the atmosphere and decay in the presence
of sodium chloride may be active causes of the rapid chalking of this
pigment at the seashore. Checking in some climates appears to proceed
rapidly on white lead paints, in a deep hexagonal form, leaving a series
of rough crests and cracks. This checking is secondary to the chalking
which takes place.
[Illustration: Corrosion cylinders used for making Quick Process White
Lead]
[Illustration: Lead Melting Pots]
=White Lead (Quick Process).= By acting on atomized metallic lead,
contained within large revolving wooden cylinders, with dilute acetic
acid and carbon dioxide, the quick-process white lead is produced. Its
value is equal to the Dutch-process white lead, and it is considered by
some as possessing greater spreading value.
[Illustration: Sheet iron box luted at bottom with water. Atomized lead,
blown into box with steam, falls to bottom and becomes hydrated (Mild
Process)]
[Illustration: _Photographs courtesy of Stowe Neal_
View of agitation tanks for making Mild Process Lead]
[Illustration: Steam Jected Pans for Drying White Lead]
=White Lead (Mild Process).= The Mild Process of manufacturing white
lead consists of first melting the pig lead and converting it into the
finest kind of lead powder, then mixing thoroughly with air and water.
The lead takes up water and oxygen and forms a basic hydroxide of lead.
Carbon dioxide gas is next pumped slowly through the cylinders which
contain the basic hydroxide of lead. The result is basic carbonate of
lead--the dry white lead of commerce. The process is called "Mild"
because it is the mildest process possible for the manufacture of white
lead. It is the only method in practical operation which does not
require the use of acids, alkalis or other chemicals, every trace of
which should be removed from the finished product by expensive purifying
processes. The failure of such washing and purifying means a product of
inferior quality, which necessarily reduces the durability of any paint
in which it is used.
=Basic Sulphate-White Lead (Sublimed White Lead).= By the action of the
oxygen of the air on the fume produced by the roasting and subsequent
volatilization of galena, this fine, white, amorphous pigment is made.
On analysis, its composition shows approximately 75% of lead sulphate,
20% of lead oxide, and 5% of zinc oxide. It has a specific gravity of
6.2. Possessed of extreme stability, it finds wide use as a constituent
of paints and as a base for tinting colors. The photomicrograph of this
pigment shows its extremely fine, amorphous nature with complete absence
of crystals. In fineness it closely approaches zinc oxide. On account of
its non-poisonous properties it is replacing corroded lead in many
places. Unified paints containing sublimed white lead are of great
value, showing upon long exposure very little decay.
[Illustration: View of Furnace for Making Sublimed White Lead]
[Illustration: View of Goosenecks Used for Collecting Sublimed White
Lead Fume]
[Illustration: Bag Room Where Sublimed White Lead is Deposited
_Photographs courtesy of Picher Lead Co._]
[Illustration: Sublimed White Lead]
[Illustration: View of largest Zinc Oxide Works in America, at Hazards,
Pa.]
=Sublimed Blue Lead.= Sublimed blue lead is made by burning coarsely
broken lumps of galena, admixed with bituminous coal, in a special form
of furnace. The fumes which are volatilized from this mixture are very
complex in their chemical make-up, and in color are white, blue, and
black. After being drawn through the cooling pipes by the suction of
huge fans, whereby the fumes are cooled, the pigment is deposited in
bags. This pigment is bluish black in color, and has been highly
recommended for use on iron and steel. Its composition runs
approximately as follows:
Lead sulphate 50%
Lead oxide 35%
Lead sulphide 5%
Lead sulphite 5%
Zinc oxide 2%
Carbon 3%
[Illustration: View of Zinc Oxide Furnaces]
[Illustration: _Photographs courtesy Geo. B. Heckel and N. J. Zinc Co._
View of Zinc Oxide Fume Pipes with electrically driven Suction Fans]
The color of the pigment is largely due to the carbon and the lead
sulphide. Its specific gravity is 6.4, and it grinds in 10% of oil to a
stiff paste, 100 lbs. of which may be thinned with about 26 lbs. of oil
to working consistency. Paint manufacturers use it in mixture with iron
oxide and other pigments for the production of paints for metal
surfaces. Wood and others have found it of great value for this purpose.
It has a tendency to chalk, but this may be overcome by admixture with
other pigments such as zinc oxide and iron oxide. Lane has found it to
be very durable when admixed with lampblack.
[Illustration: View of Bag Room receiving Zinc Oxide]
=Zinc Oxide.= This extremely white and fine pigment is prepared by the
roasting and sublimation of franklinite, zincite, and other zinc-bearing
ores largely found in New Jersey. Its purity approaches in most
instances 99.5 or more. It has a specific gravity of 5.2. On account of
its stability, whiteness, and opacity, it is invaluable as a pigment
when a constituent in a combination formula. Its extreme hardness
renders it less resistant to temperature changes, when used alone. Under
the microscope the fineness and structure of the particles are clearly
evident. The French-process zinc oxide produced in America by the
sublimation and oxidation of spelter is the purest made, and superior to
imported grades which often contain ultramarine blue as a whitening
agent.
[Illustration: Zinc Oxide]
[Illustration: Zinc Lead White]
[Illustration: Zinc Lead. By transmitted light
(_The Pigment shows black_)]
[Illustration: Lithopone]
[Illustration: Magnesium Silicate (Asbestine)]
=Zinc Lead White.= This extremely fine pigment, consisting of about
equal parts of zinc oxide and lead sulphate, results from the reduction,
volatilization and subsequent oxidation of sulphur-bearing lead and zinc
ores. It has a specific gravity of 4.4. Its slightly yellowish tint bars
it from being used alone very extensively, but when mixed with white
lead, zinc oxide and inert pigments, or used as a base for colored
paints, it is of considerable value. The magnification of the particles
shows the peculiar way in which the pigment agglomerates, and the
characteristics of a fine, uniform pigment.
[Illustration: Asbestine Mine at Easton, Pa.]
[Illustration: American Barytes. Transmitted light
(_The Pigment shows black_)]
[Illustration: German Barytes. Mag. 250 Diam.
(_The Pigment shows white_)]
=Lithopone.= Lithopone, probably the whitest of pigments, results from
the double decomposition of zinc sulphate and barium sulphide, thereby
forming a molecular combination of zinc sulphide and barium sulphate.
The peculiar property which it possesses, of darkening under the actinic
rays of the sun, makes it essential that it be combined with other, more
stable pigments to prolong its life when exposed to weather. Lithopone
contains approximately 70% barium sulphate, 25 to 28% zinc sulphide, and
as high as 5% of zinc oxide. Its specific gravity is about 4.25. It is
excellently suited for interior use in the manufacture of enamels and
wall finishes. When properly mixed with other pigments, such as zinc
oxide and calcium carbonate, fair results are obtained as a pigment for
outside work. Lead pigments are never used with lithopone, as lead
sulphide results, giving a black appearance. Its characteristic
flocculent, non-crystalline nature is plainly evident when examined
under the microscope.
[Illustration: By Polarized Light
By Transmitted Light
Barium Sulphate (Barytes)]
=Magnesium Silicate (Asbestine and Talcose).= This pigment comes in two
forms: as asbestine and as talcose (talc, etc.). The former is very
fibrous in nature and is a very stable pigment to use in the manufacture
of paint, on account of its inert nature and tendency to hold up heavier
pigments, and prevent settling. It also has the property of
strengthening a paint coat in which it is used. The talcose variety is
very tabular in form. Both varieties are transparent in oil, and very
inert. They have a gravity of about 2.7 and grind in about 32% of oil.
[Illustration: Barium Carbonate. Mag. 250 Diam.
(_The Pigment shows white_)]
[Illustration: Barium Sulphate (Blanc Fixe)]
[Illustration: Calcium Carbonate (Whiting)]
[Illustration: Calcium Carbonate. By transmitted light
(_The Pigment shows black_)]
[Illustration: Calcium Sulphate. By transmitted light
(_The Pigment shows black_)]
[Illustration: Calcium Sulfate]
[Illustration: Calcium Sulphate (Gypsum)]
[Illustration: Silica (Silex)]
[Illustration: Silex. Mag. 250 Diam.
(_The Pigment shows white_)]
[Illustration: China Clay. By transmitted light
(_The Pigment shows black_)]
=Barium Sulphate (Barytes).= By grinding the crude ore, treating with
acid to remove the iron, and finally washing, floating, and drying,
there is produced the commercial form of this valuable pigment. It is
used in large quantity as a base upon which to precipitate colors, and
also together with other white pigments in the manufacture of
ready-mixed paints. It renders the paint coating more resistant to
abrasion, and gives to the paint certain very important brushing
qualities. It is a very stable pigment, not being materially affected by
either acid or alkali, and can be used with the most delicate colors. In
oil it is transparent and must be mixed with opaque pigments when used
in ready-mixed paints. It is generally used with lighter pigments, such
as asbestine, in order to prevent settling. Under the microscope, both
by polarized and transmitted light, the sharp angles of the particles
appear distinctly, with no tendency to mass into a compact form.
Although transparent in oil, it is valuable in moderate percentage in a
ready-mixed paint.
=Barium Sulphate (Blanc Fixe).= Blanc fixe is the precipitated form of
barium sulphate, resulting from the action of soluble barium salts on
soluble sulphates. The specific gravity (4.2) of this compound is lower
than that of barytes. Possessing greater opacity in oil, it is of more
value as a paint pigment for some purposes. It comes in for its greatest
use as a base on which to precipitate lake colors. The very fine
particles show a slight tendency to agglomerate.
=Calcium Carbonate (Whiting).= The natural form of calcium carbonate,
prepared from chalk, has a much higher specific gravity (2.74) than that
of the artificial form (2.5) prepared by the precipitation of calcium
carbonate. The latter, however, possesses greater hiding properties.
Both grades find a wide use in distemper work and in the manufacture of
putty. It is often used in small percentage in many ready-mixed paints.
The photomicrograph of the pigment shows the presence of many large
particles.
=Calcium Sulphate (Gypsum).= The mineral gypsum, consisting of calcium
sulphate and about 21% of water of combination, is sometimes used as a
paint pigment after grinding and dehydration. Being slightly soluble in
water it has a tendency to pass into solution when exposed to
atmospheric agencies. It lacks hiding power in oil. Its specific gravity
is 2.3. As in the case of all pigments prepared directly from mineral
substances, the many-sized and shaped particles appear clearly when
enlarged. Partially and wholly dehydrated forms of gypsum are also used
in paint.
=Silica (Silex.)= This white pigment possesses great tooth and spreading
properties. It is of use as a wood filler and as a constituent in
combination paints. It wears especially well when used in combination
with zinc oxide and white lead. Its purity often approaches 97%. The
particles when enlarged are seen to have sharp angles and are not
uniform in size, which accounts for its marked tooth and properties.
[Illustration: Aluminum Silicate (China Clay)]
[Illustration: Ochre]
[Illustration: Raw
Burnt
Sienna]
[Illustration: Raw
Burnt
Umber]
=Aluminum Silicate (China Clay).= China clay, or aluminum silicate, is a
permanent and valuable white pigment showing very little hiding power in
oil. It is found widely distributed in granitic formations. It is very
stable, with a gravity of 2.6. Particles are found in many shapes and
sizes, showing sharp and definite angles.
=Ochre.= Ochre is a hydrated ferric oxide permeating a clay base,
largely used as a tinting material. It has a specific gravity of about
3.5, and a decidedly golden yellow color. A good quality should contain
20% or over of iron oxide. The particles of this pigment are flocculent
and very uniform in appearance.
=Sienna.= Sienna, like umber, is essentially a silicate of iron and
alumina, containing manganic oxide. It contains, however, a lower
percentage of the latter than in the case of umbers. The photomicrograph
of the burnt variety shows clearly the fine condition of the pigment,
while large particles are shown in the raw variety.
=Umber.= Umber, another naturally occurring pigment, consists of iron
and aluminum silicates, containing varying proportions of manganic
oxide, its color and tone varying according to the percentage of the
latter. The raw variety is drab in color, which in burning changes to
reddish brown. A marked percentage of large-sized particles exist in
this pigment.
=Indian Red.= Indian red is the term applied to natural hematite ore
pigments and to those produced by the roasting of copperas (iron
sulphate). They generally contain 95% or more of iron oxide, with
varying percentages of silica. The pigment is heavier (specific gravity
5.2) than that of Metallic Brown. The crystalline, mineral-like
structure of the particles differ greatly from the amorphous particles
of Metallic Brown.
=Metallic Brown.= The natural hydrated iron oxide or carbonate as mined
largely in Pennsylvania, yields, when roasted, a sesquioxide of iron
known as Metallic Brown. It contains a high percentage of alumina and
silica, and has a characteristic brown color with a gravity of 3.1. It
finds wide application as a pigment for protective purposes. The
particles when enlarged show the usual appearance of a natural compound
which has been roasted and ground.
==========+=====+===========+==========+=============+=======+=========
No. Name |Iron | Calc. | Alumina | Insoluble | Color |
|Oxide| Sulph. | | |(Silica|
+-----+-----------+(CaSO_{4})|(Al_{2}O_{3})| and |
| FeO |Fe_{2}O_{3}| | | Sili- |
| | | | | cates)|
----------+-----+-----------+----------+-------------+-------+---------
| % | % | % | % | % |
0 Bright | 0.71| 96.52 | -- | -- | .30 |Bright
Red | | | | | |Scarlet
1 Bright | .71| 95.92 | -- | -- | .30 |Scarlet
Red | | | | | |Tone
2 Indian | .57| 96.00 | .78 | 1.40 | .90 |Indian
Red | | | | | |Red,
| | | | | |Medium
| | | | | |Shade
3 Indian | 0.29| 97.82 | .85 | -- | .52 |Indian
Red | | | | | |Red,
| | | | | |Dark
| | | | | |Shade
4 Indian | 0.28| 95.72 | 1.21 | 1.26 | .58 |Indian
Red | | | | | |Red,
| | | | | |Light
| | | | | |Shade
5 Persian| 4.53| 62.25 | 1.75 | -- | 27.64 |Rich,
Gulf | | | | | |Medium
Mix | | | | | |Red
7 Native | 0.85| 89.00 | -- | 0.91 | 6.09 |Medium
Red | | | | | |Red,
Oxide | | | | | |Brownish
| | | | | |Tone
8 Special| 0.57| 43.87 | 50.88 | 2.03 | 1.30 |Scarlet
Red | | | | | |Tone
10 Red | 1.44| 60.25 | .78 | 5.41 | 15.78 |Brownish-
Oxide | | | | | |Red
11 Vene- | .30| 34.08 | 52.60 | 2.20 | 3.39 |Bright
tian | | | | | |Red-
Red | | | | | |Brown
12 B. | 0.58| 67.68 | -- | 2.48 | 1.97 |Dark Red
Oxide | | | | | |Brown
13 Vene- | 0.29| 25.92 | 58.62 | 2.16 | 1.42 |Medium
tian | | | | | |Red
Red | | | | | |Tone
14 Vene- | 0.57| 35.36 | .99 | 12.06 | 47.97 |Brown
tian | | | | | |
Red | | | | | |
15 Metal- | 2.59| 64.00 | .63 | 5.82 | 23.42 |Rich
lic | | | | | |Brown
Brown | | | | | |
16 Crimson| 0.57| 66.24 | 1.77 | 3.60 | 25.63 |Rich
Oxide | | | | | |Dark
| | | | | |Red
17 Red | 2.30| 80.39 | .37 | .03 | 9.63 |Medium
Oxide | | | | | |Brown
18 Red | 0.57| 61.28 | .97 | 2.68 | 15.94 |Light
Oxide | | | | | |Choco-
| | | | | |late
| | | | | |Brown
20 Red | 7.78| 46.72 | 1.70 | 7.64 | 20.38 |Dark
Oxide | | | | | |Reddish
| | | | | |Brown
23 Special| 0.58| 72.48 | -- | 8.80 | 4.48 |Deep
French | | | | | |Choco-
Oxide | | | | | |late
| | | | | |Brown
24 Mica- | 2.02| 86.27 | -- | 2.04 | 9.50 |Dark
ceous | | | | | |Gray
Black | | | | | |Tone
Oxide | | | | | |
25 Black |33.12| 57.12 | -- | 1.44 | -- |Jet
Oxide | | | | | |Black
26 Red | 0.57| 84.16 | 5.00 | 2.00 | .63 |Deep
Oxide | | | | | |Red
27 Special| 0.57| 38.40 | 55.62 | 2.12 | 1.53 |Medium
Red | | | | | |Red
28 Oxide C| -- | 30.40 | .94 | 13.60 | 42.30 |Brown
==========+=====+===========+==========+=============+=======+=========
=Analysis of Iron Oxide Pigments.= Because of the great consideration
now being given to iron oxide paints, the writer secured a series of
oxides widely used in this country, and has determined the most
important constituents of each.
=Basic Lead Chromate (American Vermilion).= By boiling white lead with
chromate of soda and subsequently treating with small quantities of
sulphuric acid, American vermilion, or basic lead chromate, is prepared.
It contains 98% of lead compounds, frequently free chromates, and has a
gravity of 6.8. The particles appear granular and large, frequently
assuming a square structure.
=Red Lead.= By the continued oxidation of litharge in reverberatory
furnaces, red lead is produced as a brilliant red pigment with a
specific gravity of 8.7. The pigment particles appear to be of many
sizes, showing a slight tendency to form a compact mass.
=Paranitraniline Red.= Paranitraniline red, a very bright red material
largely used in tinting paints, is prepared by diazotizing
paranitraniline in hydrochloric acid by means of sodium nitrite in the
cold. This compound is rendered insoluble when precipitated directly on
barytes, by acting on it with an alkaline solution of beta naphthol. It
is the most stable and permanent bright red organic pigment which the
paint manufacturer uses. The particles of this pigment appear in various
sizes, due, no doubt, to a massing of the particles in the precipitation
process.
=Chrome Yellow.= The neutral chromate of lead, made from either the
nitrate or acetate of lead and chromate of soda, finds wide use as a
tinting pigment. When precipitated on a white pigment base, various
trade names are given to it. The microscope shows clearly the physical
character of this pigment.
=Zinc Chromate.= This pigment is made either from zinc salts and
bichromate of potash or zinc oxide heated with chrome salts, frequently
in the presence of acid. Like the rest of the chromate pigments, it is a
very slow-drying material, often requiring over a week to set up, unless
considerable drier is added. In spite of the impurities which it
carries, it has shown itself to be one of the most inhibitive pigments
known and has demonstrated its value in even small percentages in paints
for iron and steel. It dries to a hard adherent film that tends to
protect metal from corrosion.
[Illustration: Indian Red]
[Illustration: Metallic Brown]
[Illustration: Basic Lead Chromate (American Vermilion)]
[Illustration: Red Lead]
[Illustration: Paranitraniline]
[Illustration: Chrome Yellow]
=Prussian Blue.= On oxidizing the precipitate resulting from the
interaction of solutions of prussiate of potash and copperas (iron
sulphate), Prussian blue as used in the paint trade is prepared. It has
a specific gravity of 1.9. The pigment shows an amorphous structure, the
particles varying greatly in size.
=Ultramarine Blue.= This bright blue pigment is prepared by burning
silica, china clay, soda ash and sulphur in pots or furnaces. It has a
specific gravity of 2.4. It is of little value as a paint pigment on
account of its sulphur content, which causes darkening when mixed with
lead pigments, and corrosion when applied to iron or steel. The darkness
of the photograph is due to the massing of the pigment particles.
=Chrome Green.= Chrome green is prepared as a paint pigment from nitrate
of lead, Chinese blue, and bichromate of soda. It has a gravity of 4 and
is liable to contain slight traces of lead salts. The particles when
magnified appear very fine and flocculent. This color is often
precipitated on pigments, such as barytes, which do not reduce its tone.
=Bone Black.= By grinding the carbonaceous matter resulting from the
charring of bones, in iron retorts, the pigment bone black is prepared.
It contains about 15% of carbon and 85% of calcium phosphate. It has a
gravity of 2.7. Comparatively large particles of charred bone can be
seen scattered throughout the mass, resulting from the difficulty of
grinding to a uniform size.
=Carbon Black.= This form of very pure carbon results from the
combustion of gas. Its gravity, 1.09, is lower than that of lampblack,
which shows a gravity of 1.8. It is used in much the same way and for
the same purposes as lampblack. In physical appearance it shows great
similarity to the particles of lampblack.
=Lampblack.= This pigment, made from the combustion of oils, consists
very often of more than 99% carbon. It has wonderful tinting value. The
particles show a fine, fibrous structure with a tendency toward
agglomeration. They differ greatly in physical appearance from those of
either graphite or bone black, being exceedingly more uniform than the
latter.
[Illustration: Zinc Chromate]
[Illustration: Prussian Blue]
[Illustration: Ultramarine Blue]
[Illustration: Chrome Green]
[Illustration: Bone Black]
[Illustration: Carbon Black]
=Graphite.= Graphite, both in the natural and artificial form, contains
impurities such as silica, iron oxide and alumina, but the natural form
has a much greater percentage of these foreign materials, in some cases
as high as 40%. Graphite is usually mixed with other pigments, such as
red lead and sublimed blue lead, thus serving better as a paint coating.
The difference in physical appearance of the various carbon pigments is
interesting, as each pigment has characteristics of its own. In graphite
we find a great tendency toward agglomeration or massing of particles.
=Mineral Black.= Mineral black is a pigment made by grinding a black
form of slate. It contains a comparatively low percentage of carbon and
consequently has low tinting value. It finds use as an inert pigment in
compounded paints, especially for machine fillers. The pigment has a
flocculent appearance, the particles showing a strong tendency to mass.
Photomicrographs of two combination paint pigments are here given, to
show the various pigments as they appear under the microscope, when in
combination.
PERCENTAGES OF OIL REQUIRED FOR GRINDING VARIOUS DRY PIGMENTS INTO
AVERAGE PASTE FORM
White lead (corroded) 9%
White lead (sublimed) 10%
Zinc lead (American) 12%
French process zinc oxide 17%
American process zinc oxide 16%
Blanc fixe 30%
Barytes (natural) 9%
Paris white (whiting) 20%
Terra alba (gypsum) 22%
Floated silica or Silex 26%
Kaolin (China clay) 28%
Asbestine 32%
Blue, ultramarine 27%
Blue, Chinese or Prussian 50%
Black, gas carbon 82%
Black, lamp 72%
Black, drop 60%
Black, bone 50%
Brown, mineral 24%
Brown, vandyke 50%
Chrome yellow, lemon 23%
Chrome yellow, medium 30%
Chrome yellow, orange 20%
Chrome yellow, dark orange 15%
Chrome green, Chem. pure light 21%
Chrome green, Chem. pure extra dark 25%
Chrome green, 25%, color light 13%
Chrome green, 25%, color extra dark 17%
Graphite (pure) 40%
Indian red, (98%) 20%
Ochre, yellow, American 26%
Ochre, yellow, French 28%
Ochre, golden 28%
Red, Venetian 23%
Red, Oxide 25%
Red, Tuscan 27%
Red, Turkey 28%
Red, lead 12%
Red, lake 55%
Sienna, Italian, raw 52%
Sienna, Italian, burnt 45%
Sienna, American, burnt 38%
Sienna, American, raw 40%
Ultramarine green 28%
Umber, Turkey, raw 48%
Umber, Turkey, burnt 47%
Umber, American, burnt 36%
Umber, American, raw 38%
Verona green (terra verte or green earth) 32%
Vermilion, English (quicksilver) 14%
Vermilion, American (chrome red) 16%
Paris green, American 23%
Zinc chromate (permanent yellow) 15%
[Illustration: Lampblack]
[Illustration: Graphite]
[Illustration: Mineral Black]
[Illustration: Asbestine and Whiting]
[Illustration: Silica and Asbestine]