[8]Lost in weight throughout test.
[8]Lost in weight throughout test.
[9]Gained in weight throughout test.
[9]Gained in weight throughout test.
[10]Moth got in.
[10]Moth got in.
[11]The test of this oil was made without the addition of 5 per cent. of drier, the quantity used in all the other tests.
[11]The test of this oil was made without the addition of 5 per cent. of drier, the quantity used in all the other tests.
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.[12]
[12]The author gratefully acknowledges the assistance of Dr. J. A. Schaeffer in the preparation of the photomicrographs shown in this chapter.
[12]The author gratefully acknowledges the assistance of Dr. J. A. Schaeffer in the preparation of the photomicrographs shown in this chapter.
Basic Carbonate-White Lead.Thispigmentis 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 and15% 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.
Cerrusite Crystals in Old Dutch Process WhiteCrystals of Cerussite in Old Dutch Process White Lead. (Greatly magnified)
Crystals of Cerussite in Old Dutch Process White Lead. (Greatly magnified)
White Lead Quick ProcessWhite Lead (Quick Process)
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 whichaccelerate 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.
Corrosion Cylinders for making Quick Process White LeadCorrosion cylinders used for making Quick Process White Lead
Corrosion cylinders used for making Quick Process White Lead
Lead Melting PotsLead Melting Pots
Lead Melting Pots
White Lead (Quick Process).By acting on atomized metallic lead, contained within large revolvingwooden cylinders, with dilute acetic acid and carbon dioxide, thequick-process white leadis produced. Its value is equal to theDutch-process white lead, and it is considered by some as possessing greater spreading value.
Sheet iron box for hydrating LeadSheet iron box luted at bottom with water. Atomized lead, blown into box with steam, falls to bottom and becomes hydrated (Mild Process)
Sheet iron box luted at bottom with water. Atomized lead, blown into box with steam, falls to bottom and becomes hydrated (Mild Process)
Agitation Tanks for making Mild Process LeadPhotographs courtesy of Stowe NealView of agitation tanks for making Mild Process Lead
Photographs courtesy of Stowe Neal
View of agitation tanks for making Mild Process Lead
White Lead (Mild Process).The Mild Process of manufacturing white lead consists of firstmelting the pig leadand converting it into the finest kind of lead powder, then mixing thoroughly withair and water. The lead takes up water and oxygen and forms a basic hydroxide of lead. Carbon dioxide gas is next pumped slowly through thecylinderswhich 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.
Steam Jected PansSteam Jected Pans for Drying White Lead
Steam Jected Pans for Drying White Lead
Basic Sulphate-White Lead (Sublimed White Lead).By the action of the oxygen of the air on the fume produced by theroastingand 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. Thephotomicrographof 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.
Sublimed White Lead FurnaceView of Furnace for Making Sublimed White Lead
View of Furnace for Making Sublimed White Lead
Goosenecks Used for Collecting Sublimed White Lead FumeView of Goosenecks Used for Collecting Sublimed White Lead Fume
View of Goosenecks Used for Collecting Sublimed White Lead Fume
Bag Room for Deposit of Sublimed White LeadBag Room Where Sublimed White Lead is DepositedPhotographs courtesy of Picher Lead Co.
Bag Room Where Sublimed White Lead is Deposited
Photographs courtesy of Picher Lead Co.
Sublimed White LeadSublimed White Lead
Sublimed White Lead
Hazards, Pa. Zinc Oxide WorksView of largest Zinc Oxide Works in America, at Hazards, Pa.
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:
Zinc Oxide FurnacesView of Zinc Oxide Furnaces
View of Zinc Oxide Furnaces
Zinc Oxide Fume Pipes with electric suction FansPhotographs courtesy Geo. B. Heckel and N. J. Zinc Co.View of Zinc Oxide Fume Pipes with electrically driven Suction Fans
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 atendency 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.
Bag Room receiving Zinc OxideView of Bag Room receiving Zinc Oxide
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 microscopethe 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.
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. Themagnificationof the particles shows the peculiar way in which the pigment agglomerates, and the characteristics of a fine, uniform pigment.
Easton, Pa. Asbestine MineAsbestine Mine at Easton, Pa.
Asbestine Mine at Easton, Pa.
American BarytesAmerican Barytes. Transmitted light(The Pigment shows black)
American Barytes. Transmitted light(The Pigment shows black)
German BarytesGerman Barytes. Mag. 250 Diam.(The Pigment shows white)
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 suitedfor 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 examinedunder the microscope.
Magnesium Silicate (Asbestine and Talcose).This pigment comes in two forms: asasbestineand 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.
Barium CarbonateBarium Carbonate. Mag. 250 Diam.(The Pigment shows white)
Barium Carbonate. Mag. 250 Diam.(The Pigment shows white)
Calcium CarbonateCalcium Carbonate. By transmitted light(The Pigment shows black)
Calcium Carbonate. By transmitted light(The Pigment shows black)
Calcium SulphateCalcium Sulphate. By transmitted light(The Pigment shows black)
Calcium Sulphate. By transmitted light(The Pigment shows black)
Calcium SulphateCalcium Sulfate
Calcium Sulfate
SilexSilex. Mag. 250 Diam.(The Pigment shows white)
Silex. Mag. 250 Diam.(The Pigment shows white)
China ClayChina Clay. By transmitted light(The Pigment shows black)
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 pigmentswhen used in ready-mixed paints. It is generally used with lighter pigments, such as asbestine, in order to prevent settling. Under themicroscope, 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. Thevery fine particlesshow 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. Thephotomicrographof 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 whenenlarged. 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 whenenlargedare seen to have sharp angles and are not uniform in size, which accounts for its marked tooth and properties.
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.Particlesare 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. Theparticlesof 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. Thephotomicrographof 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-sizedparticlesexist 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 theparticlesdiffer 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. Theparticleswhen enlarged show the usual appearance of a natural compound which has been roasted and ground.
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. Theparticlesappear 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 pigmentparticlesappear 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. Theparticlesof 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. Themicroscopeshows clearly the physical character of this pigment.
Zinc Chromate.Thispigmentis 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.
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, theparticlesvarying 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 thephotographis 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. Theparticleswhen 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 largeparticlesof 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. Inphysical appearanceit 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. Theparticlesshow 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.
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 ofparticles.
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, theparticlesshowing a strong tendency to mass.
Photomicrographs of two combination paint pigments areheregiven, to show the various pigments as they appear under the microscope, when in combination.
For the paint chemist who desires to familiarize himself with the more recent analytical methods worked out in American laboratories, reference may be had to treatises on the analysis of paints, by Gardner and Schaeffer,[13]and Holley and Ladd.[14]Analytical methods are not included in this chapter, the writer’s desire being to treat the subject from the standpoint of the physical properties of painting materials. The work outlined herein is of a nature that affords a wide field of research, and a brief study will doubtless suggest similar work to the student of paint.