Please see [Transcriber's Notes] at the end of this document

PAINT TECHNOLOGY AND TESTS

PAINT TECHNOLOGY
AND TESTS.

BY

HENRY A. GARDNER

Assistant Director, The Institute of Industrial Research, Washington, D. C.
Director, Scientific Section, Paint Manufacturers’ Association of the United States, etc.

McGRAW-HILL BOOK COMPANY
239 WEST 39TH STREET, NEW YORK
6 BOUVERIE STREET, LONDON, E.C.
1911

Copyright, 1911, by the McGraw-Hill Book Company

THE·PLIMPTON·PRESS·NORWOOD·MASS·U·S·A

TO
MY MOTHER

PREFACE

A few years ago the producer and consumer of paints possessed comparatively little knowledge of the relative durability of various pigments and oils. There existed in some cases a prejudice for a few standard products, that often held the user in bondage, discouraging investigation and exciting suspicion whenever discoveries were made, that brought forth new materials. Such conditions indicated to the more progressive, the need of positive information regarding the value of various painting materials, and the advisability of having the questions at issue determined in a practical manner.

The desire that such work should be instituted, resulted in the creation of a Scientific Section, the scope of which was to make investigations to determine the relative merits of different types of paint, and to enlighten the industry on various technical problems. Paint exposure tests of an extensive nature were started in various sections of the country where climatic conditions vary. This field work was supplemented in the laboratory by a series of important researches into the properties of pigments, oils, and other raw products entering into the manufacture of protective coatings. The results of the work were published in bulletin form and given wide distribution. The demand for these bulletins early exhausted the original impress, and a general summary therefore forms a part of this volume.

The purpose of the book is primarily to serve as a reference work for grinders, painters, engineers, and students; matter of an important nature to each being presented. Without repetition of the matter found in other books, two chapters on raw products have been included, and they present in condensed form a summary of information that will prove of aid to one who desires to become conversant with painting materials with a view to continuing tests such as are outlined herein. In other chapters there has been compiled considerable matter from lectures and technical articles presented by the writer before various colleges, engineering societies, and painters’ associations.

The writer wishes to gratefully acknowledge the untiring efforts of the members of the Educational Bureau of the Paint Manufacturers’ Association, whose early endeavors made possible many of the tests described in this volume. Kind acknowledgment is also made to members of the International Association of Master House Painters and Decorators of the United States and Canada, who stood always ready to aid in investigations which promised to bring new light into their art and craft.

HENRY A. GARDNER.

Washington, October, 1911.

CONTENTS

PAINT TECHNOLOGY

CHAPTER I

PAINT OILS AND THINNERS

Constants and Characteristics of Oils and Their Effect upon Drying. An attempt has been made to give in this chapter a brief summary of the most important characteristics of those oils finding application in the paint and varnish industry. For methods of oil analysis, the reader is referred to standard works on this subject; the analytical constants herein being given only for comparative purposes.

It is well known that one of the most desirable features of a paint oil is the ability to set up in a short period to a hard surface that will not take dust. This drying property is dependent upon the chemical nature of the oil. If it is an unsaturated compound, like linseed oil, rapid absorption of oxygen will cause the film to dry rapidly and become hard. If the oil be of a fully satisfied nature, like mineral oil, oxygen cannot be taken up to any great extent and drying will not take place. The various animal and vegetable oils differ in their power of oxygen absorption to a lesser or greater extent. This difference is referred to by the chemist in terms of the iodine value. The iodine value of linseed oil is approximately 190, meaning that one gram of the oil will take up 190 centigrams of iodine. Oils with high iodine values have good drying powers, while those with low iodine values are, as a rule, very slow drying in nature.

For a description of the working and drying properties of various oils used in paints, see [Chapter XIV]. The oxygen absorption of various oils and mixtures is shown in [Chapter II].

Linseed Oil. The seed of the [flax plant] which is extensively grown in North Dakota, Argentine Republic and Russia, contains approximately 36% of oil which may be obtained by grinding, heating, and expression. Ripe native seed generally produces a pale oil of little odor; the oil from Argentine seed often having a greenish tint and an odor resembling sorghum. While filtering, pressing and ageing will remove considerable of the (“foots”) mucilaginous matter, phosphates, silica, etc., from the oil, the better grades which are intended for varnish making are often refined with sulphuric acid. A light colored oil which may be heated without “breaking” results from this treatment, but such oils are apt to contain considerable free fatty acid, unless they are washed with alkali subsequent to the sulphuric acid treatment. On account of its rapid drying properties and general adaptability for all classes of paints and varnishes, linseed oil has never been supplanted by any other oil. Chemically it consists of the glycerides of linoleic, oleic, and isolinoleic acid, its constitution being responsible for its very high iodine value.

Field of Flax in bloom in North Dakota

Boiled linseed oil, a heavier and darker product, is made by heating the raw oil in open kettles to high temperatures, generally with the addition of metallic driers such as litharge, and black manganese. The resinates of lead and manganese are often added to oil heated at a lower temperature, to obtain a boiled oil of lighter color.

New type of Flax Harvester which pulls plant up by the roots, thus preventing infection of soil

Modern Concrete Elevators for storing Flaxseed

View of Linseed Oil Factory showing hydraulic press, tanks, etc.

Photographs courtesy of Spencer Kellogg Sons

Flaxseed Crushers

Filter Presses for removing extraneous matter from linseed oil

Linseed Cake from Oil Press

Glycine Hispida
Mammoth soya bean plants

Photographs courtesy of David Fairchild, Plant Explorer, U. S. Dept. of Agriculture

Glycine Hispida
Soya bean plants under cultivation at Arlington, Va.

By blowing air through linseed oil that has been heated to approximately 200 degrees Fahrenheit, either with or without drier, heavy bodied oils are obtained, which find special application in varnishes and technical paints. As the viscosity of these oils increase, the iodine values decrease, and a slight rise in saponification value and specific gravity is observed. The following analyses of various types of linseed oil were recently made by the writer:

Soya Bean Oil. The [soya plant] which is extensively cultivated in Asia produces a [seed] bearing up to 22% and over of a golden colored oil having a peculiar leguminous odor. The oil, which probably consists of the glycerides of oleic, linoleic, and palmitic acids, is secured by crushing, steaming and pressing the seed. There are several varieties of the plant, and they are said to be the best annual legume for forage, the straw and fruit being rich in nitrogen and very fattening as a cattle food. Soya may be grown in nearly any country and is a great carrier of nitrogen to land deficient in this element. Although the oil has been used abroad for many years for soap-making purposes, its use as a drying oil is comparatively recent; being introduced into the paint industry of the United States during the year 1909, when linseed oil started on its phenomenal rise in price.

Glycine Hispida
Mammoth soya bean plant

Glycine Hispida
Soya bean plant, showing nitrogen gathering tubercles on roots

The oil has given fair service in some paints when mixed with upwards of 75% of pure linseed oil. It is of a semi-drying nature, but may be made to dry rapidly when mixed with manganese and lead linoleate driers. By compounding it under heat with tung oil and rosin, a substitute for linseed oil is produced, which some claim to be quite valuable.

[Table I] gives the constants of several samples of soya oil examined by the writer. [Table II] shows the iodine value of mixtures of soya and linseed oils. [Table III] shows the results of drying experiments on soya oils containing different percentages of lead and manganese driers.

TABLE I

Chemical Characteristics of Soya Bean Oil

TABLE II

Iodine Values of Linseed Oil and Mixed Oils

TABLE III

Soya Bean Oil and Lead Drier

Soya Bean Oil and Manganese Drier

Soya Bean Oil, Manganese and Lead Drier

Tung Oil. There are grown in China and Japan many varieties of the “[aleurites cordata],” popularly known as the tung tree. This tree bears great quantities of large sized [nuts] containing as high as 40% of an oil which yields itself in a viscous yellow form upon heating and crushing of the fruit. The raw oil, which chemically consists of the glycerides of oleic, oleo-margaric, and probably isomeric acids, is distinguished by its rapid drying properties. When spread in a thin layer it produces a hard film with an opaque frosted surface, often showing a tendency to wrinkle. Treated tung oil will dry to a clear, water-shedding, elastic film. This oil is made by heating the raw tung oil at a comparatively low temperature with other oils and a metallic drier such as litharge.

Photographs courtesy of David Fairchild

Aleurites Cordata (Chinese Wood Oil) Barrel Factory at Cooperage Shop

Photographs courtesy of David Fairchild

Aleurites Fordii (Chinese Wood Oil)
Fruit from trees at the end of fourth year

The affinity of tung oil for rosin has resulted in the production of a series of moderate-priced varnishes most suitable for use in floor and deck paints or wherever great hardness is required. These varnishes are also finding application in the manufacture of concrete, steel, and flat wall paints; being especially suitable for the above purposes when compounded with kauri gum japan.

Aleurites Fordii
Wood Oil tree, thirty feet high and three feet in diameter, on banks of Yangtse River, Western Szechuan, China. Opium Poppy in the foreground

Aleurites Cordata
Flowering specimen of the Chinese Wood Oil tree at Riverside, California, planted in 1907. Photograph taken in 1910, when tree had borne fifty fruits

During the boiling of raw tung oil the temperature must not exceed much over 400 degrees Fahrenheit. Otherwise a peculiar “hamming” will take place, the whole mass becoming solid and of no further value as a varnish or paint vehicle. Some peculiar internal disturbance or rearrangement of the molecules is evidently effected by heat, and although the reaction is not clearly understood, it has been ascribed to auto-polymerization. Scott has stated that the phenomenon of gelatinization is due to the exposure of the surface of the oil to the air, and that boiling in vacuo obviates such results. The lusterless surface produced when tung oil varnishes are dried in vitiated air would tend to confirm the conclusion that the oil is very subject to atmospheric influences.

Lumbang Oil, which is obtained from a tropical species of Tung, is very similar in appearance and properties to Linseed Oil.

Constants of Tung Oils

Photographs courtesy Alpin I. Dunn

Menhaden Net drying in the Sun

Transporting Menhaden from net to deck of boat, in swinging basket

A big catch of Menhaden made off Narragansett Bay

Menhaden Oil. Of all the marine-animal oils, such as seal, herring, sardine, whale, and menhaden, the latter is the most valuable. It is produced by steam digestion and pressure of the [menhaden or “piogey” fish], which are caught in great quantities off the Atlantic Coast. Prompt cooking and treatment of the fish results in a light-colored oil having very little odor, the residue left in the presses being of great value as a fertilizer. Although several grades of oil termed crude, brown, light, etc., are produced, the most satisfactory for use in paint is that grade termed “light winter pressed.” This oil is of a pale straw color and has a high iodine number which is responsible for its rapid drying value. It contains less of the stearates that precipitate from crude oil, but sufficient to render its film water-shedding and elastic. The presence of too great a quantity of stearates is apt to result in a very soft film, and the use of hard driers, such as the metallic tungates, is therefore advisable with menhaden oil. When mixed with linseed oil paints the odor of menhaden oil is sometimes noticeable, but it disappears entirely after such paints are applied. Its use with linseed oil in technical paints exposed to the salty air of the Coast has given good results, often preventing “checking” and “chalking.”

The following constants were determined on samples of menhaden oil received in the writer’s laboratory:

Whale Oil. While ordinary whale oil is too dark and odorous to ever come into extensive use as a paint oil, it is probable that the refined oil will be utilized in the manufacture of certain technical paints. Whale oil is boiled from chopped whale blubber, the first trying being the lightest in color, while the later tryings, as well as the product made from bones, are of darker color and of very bad odor. Oil of mirbane is often used to mask this odor. The oil contains large quantities of stearin and palmitin, as well as wax-like constituents which are apt to be thrown out of solution in very cold weather, or when the oil is mixed with other oils. The refined oil, when ground with lead and zinc pigments and mixed with equal parts of linseed oil and treated tung oil, dries to an elastic and soft film. Experiments are being made to utilize whale oil in the linoleum industry.

The analyses of samples of whale oil tested by the writer are as follows:

Sunflower Oil. Sunflower oil is produced largely in Russia and Hungary, finding favor in those countries as an edible oil. The ripe [seeds] of the sunflower plant contain over 30% of oil which is very pale in color and of a pleasant smell. It has been found that sunflowers may be grown to advantage in dry parts of the United States, and if suitable yields are obtained from a few experimental acres now being cultivated, the industry may receive encouragement in this country. The oil should be well suited for varnish making, and although the iodine number is not very high, it dries quite rapidly.

Russian Sunflower Seeds

Constants of Sunflower Oil

Cottonseed Oil. This oil is expressed from the seed of the cotton plant, varying in color according to the time of its pressing and degree of refinement. Being edible as well as highly suited for soap making, very little of it comes into the market as a paint oil. It contains large quantities of stearin and has a low iodine value, making it a slow drying oil. Some samples are extremely light in color and contain less mucilaginous matter and foots than is present in ordinary varieties.

Constants of Cottonseed Oil

Corn Oil. As a by-product in the manufacture of starch and alcoholic liquids, this material comes into the market having a golden yellow color, and an odor resembling fermented grain. It has a lower drying value than cottonseed oil, and its use in the paint industry will probably be limited to color grinding, where an oil with a semi-drying value is often desired. Like cottonseed oil, it belongs more properly to the soap oil class. It contains glycerides of linoleic and especially palmitic acid.

Analysis of Corn Oil

Rosin Oil. By the dry distillation of rosin, there is yielded a series of heavy dark oils consisting principally of hydrocarbons, resinous bodies, and free acid. These oils vary in their saponification number from 10 to 60, while their unsaponifiable value averages about 80. Of the grades termed first, second, third, and fourth run, the latter two are superior for use in paints, as a rule containing less free acid than the preliminary runs. Treatment with steam and alkali serve to neutralize the acid nature of the oils and to remove impurities. Refined oils are lighter in color and are often blown and bodied to fairly rapid drying products, especially when treated with manganese driers. Rosin oils are seldom used with lead pigments, on account of the presence of sulphur in the oils, which would result in darkening. Rosin oil paints work very smoothly, even when they are curdled, producing glossy surfaces. The rapid checking of rosin oil paints on wooden surfaces bars the use of this oil for such purposes.

Analyses of Rosin Oils

Hydrocarbon Oils. Several grades of neutral or mineral oils, varying somewhat in gravity, color, and quality, are produced as the last distillate in the refining of petroleum. These oils when mixed with drying oils and strong driers find application in the manufacture of some freight-car, barn, and other paints which sell at a low price. A small percentage of mineral oil is said to be valuable in structural steel paints, acting as a preventative of hard drying and thus keeping the film soft and elastic. Streaking and sweating is apt to ensue if any great quantity is used. Mineral oils have a characteristic bloom, showing a greenish fluorescence when examined by transmitted light. This bloom is due to the presence of some strongly fluorescent material which is shown up with intensity when mineral oils are exposed to ultraviolet rays such as emanate from an enclosed arc light. Outerbridge[1] first proposed this test for mineral oils, and he has worked out a “fluorescent scale,” by which very small percentages of hydrocarbon oils may be detected in other oils. Several types of so-called debloomed oil have been placed upon the market, and although such oils appear under ordinary light conditions to be free from bloom, they fluoresce quite strongly when given the Outerbridge test.

[1] Alexander E. Outerbridge, Jr.: “A Novel Method of Detecting Mineral Oil and Resin Oil in Other Oils.” Proc. 14th Annual Meet., Amer. Soc. for Testing Mater., Atlantic City, N.J., June 28, 1911.

View of Stills Where Petroleum Paint Thinners are Manufactured (Waverly)

Analysis of Debloomed Mineral Paint Oil[2]

[2] Oil of mirbane present, probably as a deblooming agent, or to mask the odor.

Pine Oil. This oil is produced by the redistillation of the heavy, high boiling point fractions resulting from the steam distillation of wood turpentine. It is a heavy straw-colored oil, and should be of some use in the paint and varnish industry, where a high boiling point solvent with an oxidizing principle is desired. It will probably find application in the manufacture of Baking Japans, Asphalt Paints and Enamels. Its oxidizing and solvent values are very high. It has a distinctive sweet pine smell, which makes it popular in the manufacture of turpentine substitutes from petroleum spirits.

The writer has examined samples of this material, and the following appear to be of the best grade:

Constants of Pine Oils

Turpentine. By direct fire or steam distillation of the sap drippings collected in pockets cut into pine trees, there is obtained the turpentine of commerce. It consists largely of pinene and isomeric terpenes, and has the property of attracting oxygen, with the formation of peroxides which stimulate the drying of oils. It is a high-grade solvent for various gums, and is therefore used in the manufacture of many lacquers as well as for thinning down oil-gum varnishes.

Requisite Constants of Pure Gum Turpentine

Wood Turpentine. High-grade wood turpentine is now produced by the steam distillation of finely cut fat pine wood. The lower-grade qualities are often produced from the destructive distillation of sawdust, stumpage, etc., and these products, on account of their content of formaldehyde, are objectionable in odor. In the steam distillation process, however, a high quality product is obtained by cutting out the heavy fractions and redistilling the lower and purer fractions. It has a high oxidizing value, causing the rapid drying of paints and varnishes to which it has been added. Its solvent value is often greater than that of gum turpentine. When properly refined it has a sweet smell and is to be highly recommended.

Analyses of samples of pure wood turpentine which have come to the writer for examination follow:

Petroleum Spirits. There are produced from Texas crude oil which has an asphaltum base, and Pennsylvania crude oil which has a paraffin base, high boiling-point petroleum spirits which have come into wide use as paint and varnish thinners. When such materials have the proper evaporating value, high flash-point and freedom from sulphur, they are to be highly recommended as paint thinners. The following shows the analyses of a few of these materials examined in the writer’s laboratory:

Petroleum Spirits

Benzol. “Solvent naphtha” or 160-degree benzol is a product obtained from the distillation of coal tar, differing from benzine, a product obtained from the distillation of petroleum. It is a valuable thinner to use in the reduction of paints for the priming of resinous lumber and refractory woods such as cypress and yellow pitch pine. The penetrating and solvent values of benzol are high, and it often furnishes a unison between paint and wood, that is a prime foundation to subsequent coatings, preventing the usual scaling and sap exudations which often appear on a painted surface. Because of the great solvent action of benzol, it should never be used in second and third coatings. The writer has successfully painted inferior grades of cypress with a paint containing benzol in the priming coat.

Benzine. Benzine is seldom used in paints on account of its rapid evaporation, which is apt to cause pinholing of films and other surface defects. In paints of the dipping type where rapid evaporation is essential, benzine finds its widest application.

CHAPTER II

A STUDY OF DRIERS AND THEIR EFFECT

The proper drying of oils and their behavior with various siccatives in varying quantity is an interesting problem, and obviously of considerable importance from a practical standpoint. Unfortunately there is a decided scarcity of reliable literature dealing with the subject for the guidance of those concerned in the manufacture or application of siccative products. Furthermore, when the problem is investigated, it is not difficult to see why this is so.

Uniform Conditions. At a glance it is evident that a decided obstacle in experimentation on the drying properties of oils is the difficulty in obtaining identical conditions for comparative purposes. Inasmuch as a multitude of factors, such as uniformity and homogeneity of the driers and the oils themselves, intensity and source of light, temperature, uniformity of application, and many others, play a decisive part in the siccative tendencies of oils, the resources and ingenuity of the chemist engaged in the research are severely taxed.

Oxygen Absorption. It is a well-known fact that linseed oil, when applied to a clean surface, such as a glass plate, will undergo oxidation and take up oxygen to the extent of about 16%, forming a hard, elastic, non-sticky product which has been called linoxyn. This material, unlike the oil from which it has been formed, is insoluble in most solvents. Other oils, such as cottonseed, hemp, rape, olive, etc., are more fully satisfied in nature and have not the power to absorb the amount of oxygen taken up by linseed oil.

In carrying out the following tests, on the drying of oils, a quantity of pure linseed oil of the following analysis was secured:

This oil was distributed into a number of 8-oz. oil sample bottles, and to a series of these bottles was added varying quantities of a very concentrated drier made by boiling oil to 400 degrees Fahrenheit in an open kettle, with the subsequent addition of lead oxide. The amount of drier added to each bottle varied according to the percentage desired; being calculated on the lead content of the drier, which was very accurately determined by analysis.

There was secured in this manner a series of oils containing varying amounts of lead oxide, and from this lot was selected a certain number of samples which would be representative and typical of paint vehicles now found in the market.

Another series of tests were made by combining with a large number of samples of pure linseed oil as used above, various percentages of a manganese drier made by boiling oil at 400° F. and incorporating therewith manganese dioxide.

Still another series of tests were made upon a number of oils into which were incorporated various small quantities of lead oxide and manganese oxide together, using the standard driers made in the above manner, all of which were carefully analyzed to determine their contents.

In view of the errors in manipulation that could occur where so many tests were made, it was not deemed advisable, in carrying out the tests, to use glass plates on which only a minute quantity of oil could be maintained. A much better solution of the difficulty presented itself in using a series of small, round, crimped-edge tin plates, about three inches in diameter, such as are used for lids of friction-top cans.

With paints it is impossible to secure films as thin as those presented by layers of oil on glass, nor would it be desirable to secure films of this same relative thickness. For this reason an endeavor was made to conduct the following tests with films of the same relative thickness as that possessed by the average coating of paint. The drying of the films did not take place in the same short period, nor in the same ratio, as with the thin layer that is secured by flowing oil upon glass. The results, however, are more practical, and of greater value to the manufacturer.

The cans were carefully numbered in consecutive order, corresponding to the numbers on the various samples of oil. A very small quantity of oil was placed in each of the can covers, which were previously weighed, and allowed to distribute itself over the bottom surface thereof. Reweighing of the covers gave the amount of oil which was taken for each test. The test samples in the covers were all placed in a large box with glass sides, having a series of perforated shelves. In the side of this box is an opening through which a tube was passed, carrying a continual current of air washed and dried in sulphuric acid. Oxidation of the oil films commenced at once, and the amount of oxygen absorbed was determined at suitable periods by weighing, the increase in weight giving this factor. This test was kept up for a period of twenty days.

A test was also made in the same manner with a current of damp air passing into the box, to observe the relative oxidation under such conditions. A chart of the results obtained has been made ([Table VI]), to show the effect of the various driers.

Results of Tests. The following outline will present to the mind of the reader the most salient points which have been gleaned from these experiments, and which should give the manufacturer definite knowledge as to the best percentage of oxides to use either in boiled oil, paints or varnishes.

In the case of lead oxide, an increase in the percentage of lead oxide in the oil causes a relative increase in the oxygen absorption, but when a very large percentage of lead has been added, the film of oil dries to a leathery skin.

In the case of manganese oxide, the increase in oxygen absorption on the first day is much more pronounced than is the case with lead oxides. Furthermore, the oxidation of manganese oils seems to be relative to the increase in manganese up to a certain period, when the reverse of this law seems to take place, and beyond a certain definite percentage of manganese, added percentages seem to be of no value. It was furthermore observed that the films dry to a more brittle and harder skin than is the case when lead oxide is used. The oxygen absorption with oils high in manganese has been noticed to be excessive, and the film of oil becomes surface-coated, drying beneath in a very slow manner; a condition that often leads to checking. The critical percentage where the amount of manganese appears to give the greatest efficiency seems to be 0.02%. This critical percentage, as it may be termed, should not be exceeded, and any added amount of manganese has the effect of making the film much more brittle and causes the so-called “burning up” of the paint. The loading of paint with drier and the bad result therefrom may be explained to some extent from the above results.

TABLE VI—Linseed Oil and MnO2 (Manganese) Drier—Test No. 1

TABLE VII—Linseed Oil and MnO2 (Manganese) Drier—Test No. 2 (Check)

TABLE VIII—Linseed Oil and PbO (Lead) Drier

TABLE IX—Linseed Oil and PbO (Lead) and MnO2 (Manganese)—Combination Drier

In the same way with lead driers, excessive amounts of lead oxide seem to have no beneficial effects on the drying of an oil, and when the percentage which seems to be the most beneficial, namely 0.5% lead oxide, is exceeded, the film is apt to become brittle.

Oils containing lead oxide driers are less influenced in their drying tendencies by conditions of moisture in the atmosphere than oils containing manganese, but frequently, however, the former dry much better in a dry atmosphere. As a general rule, varnishes rich in manganese dry more quickly in a dry atmosphere, while those containing small quantities dry more quickly in a damp atmosphere.

Volatile Products Formed. It was furthermore noticed in these tests that sulphuric acid, placed in dishes on the bottom of the large box in which the samples of oil were drying, was discolored and turned brown after several days, showing that the acid had taken up some material of a volatile nature that was a product of the oxidation.

Another curious feature of these tests was the development of a peculiar aromatic odor which was given off by the oils upon drying in dry air. When the oils were dried in moist air, a rank odor resembling propionic acid was observed, and this led the observer to believe that a reaction was effected by the absorbed oxygen, that caused the glycerin combined with the linoleic acid as linolein to split up into evil-smelling compounds. It has been suggested that the oxygen first attacks the glycerin, transforming it into carbonic acid, water, and other volatile compounds, which are eliminated before the oil is dried to linoxyn. Toch,[3] however, has shown that the drying of linseed oil gives off only very small percentages of carbon dioxide. Mulder has observed that in the process of linseed oil being oxidized, glycerin is set free, which becomes oxidized to formic, acetic, and other acids, while the acid radicals are converted by oxygen into the anhydrides, from which they pass by further oxidation into linoxyn.

[3] Toch: The Chem. and Tech. of Mixed Paints, p. 89. D. Van Vostand Co., N. Y.

Auto-Oxidation of Oil. The theory of auto-oxidation of linseed oil has been very ably treated by Blackler, whose experiments indicated that during the drying process the slow absorption of oxygen was, at a critical period, followed by a rapid absorption, which he attributes to the presence of peroxides. The materials produced by this peroxide formation may act as catalyzers and accelerate the formation of more peroxide. Lead and manganese oxides may also be oxidized to peroxides by the action of oxygen, and in this event might act as very active catalyzing agents or carriers of oxygen. Blackler’s statement, that the presence of driers do not increase, but have a tendency to decrease the initial velocity of oxygen absorption, has been confirmed by these experiments, but it has been noticed throughout the tests that the driers have an accelerative action at a later period.

Effect of Metals on Drying of Oils. Some most interesting results were secured by dipping extremely fine copper gauze into linseed oil, and then suspending the gauze in the air. The adhesion of the oil to the copper caused the formation of films between the network, and remarkable drying action was observed. The copper or any superficial coating of copper oxide which may have been present on the metal, undoubtedly affected the result to some extent. It has been found that metallic lead is even more efficient than copper in this respect, but this may be due to the action of free acid in the linseed oil, forming lead linoleates, products that greatly accelerate drying. Another interesting experiment was made by immersing pieces of gauze cloth in linseed oil. After the excess oil had been removed, by pressing, the cloth was again weighed to determine the amount of oil used for the experiment. The increase in oxygen absorption in this case was very rapid, and the result obtained confirmed the results in the other experiments.

In order to secure a more evenly distributed state of the oil, tests were conducted by saturating pieces of stiff blotting papers, and, after exposure, weighing as usual.

Influence of Light. The influence of light on the drying of oils is unquestionably a potent one. The practical painter knows that a certain varnish will dry quicker when exposed to the light than when in the dark.

Chevreul was one of the first pioneers in this field of research to observe the effects of colored lights on drying, and he claimed that oil exposed under white glass dried more rapidly than when exposed under red glass, which eliminates all light of short wave lengths.

Genthe obtained interesting results in the drying of oil submitted to the effect of the mercury lamp. Oxidation without driers was effected probably through the formation of peroxides. In commenting on this subject, Blackler[4] gives a description of the use of the Uveol Lamp, which is similar to the mercury lamp, but has, instead of a glass casing which cuts off the valuable rays, a fused-quartz casing which allows their passage.

[4] M. B. Blackler: “The Use and Abuse of Driers,” P. and V. Society, London, Sept. 9, 1909.

Driers in Boiled Oil. In the boiling of linseed oil, by certain processes the oil is heated to 250° F. and manganese resinate is incorporated therein. It goes into solution quite rapidly. In other processes the oil is heated to 400° F. or over, and manganese as an oxide is boiled into the oil. Although it is unsafe to say that a small percentage of rosin, such as would be introduced by the use of resinate driers, is not harmful, yet it appears that this process should give a good oil, inasmuch as it has been found that no matter whether the manganese is added to the oil, as a resinate, borate or oxide, practically the same drying effect is noticed in every case where the percentage of manganese is the same. It is the opinion of some, however, that the resinate driers are not as well suited for durability as oxide driers. However, if a boiled oil is found to contain on analysis a small percentage of rosin less than 0.5% or a percentage only sufficient to combine with the metal present, it should not be suspected of adulteration. Practical tests should be made with such oil along with an oil made with an oxide drier, before pronouncing on their relative values. Inasmuch as the addition of certain driers to linseed oil lessens the durability of the film, it is more practical to use the smallest amount of drier that will serve the purpose desired, that is, set the oil up to a hard condition which will not take dust and which will stand abrasion.

The results of this investigation would indicate that when lead or manganese linoleates are used, the most efficient drying is shown with 0.5% lead or with 0.02% manganese, or with a combination of 0.5% lead and 0.02% manganese.

Until more definite results have been obtained with the tungates, which will probably prove of exceptional interest as driers, the above driers will probably be used to the greatest extent.

Co-operative Drying Tests. A series of important drying tests made by members of a special committee[5] appointed by the American Society for Testing Materials, of which the writer was chairman, is herewith shown:

[5] Sub-Committee C of Committee D-1, on Testing Paint Vehicles. Proc. Amer. Soc. for Test. Mater., 1911.

“At the January meeting of Committee D-1, a sub-committee consisting of the following members was appointed to investigate paint vehicles:

“At a subsequent meeting of the sub-committee it was determined to start the investigations with a series of tests on certain drying, semi-drying, and non-drying oils, determining their drying values, rate of oxygen absorption, etc., when spread out in thin films. A quantity of the following oils was selected for the tests and subsequently secured from sources known to be reliable:

[6] The drier used, upon analysis, showed the presence of 4.36% PbO and 2.51% MnO2.

[7] The lumbang and perilla oils were imported and arrived subsequent to the starting of the tests. They were therefore not included in the tests.

“Four-ounce sample bottles of each oil were sent to the Committee members, with the request to proceed with the tests along the lines agreed upon at the Committee meeting. The instructions for making these tests are outlined as follows:

(a) A series of small glass plates, approximately 5 by 7 ins., are to be prepared by each member of the Committee. These plates are to be thoroughly cleaned and carefully numbered and weighed upon a chemical balance. The oils to be used for the tests are to be numbered corresponding to the plates. A test of each oil is to be made by painting it upon the surface of a glass plate with a camel’s-hair brush, subsequently weighing the plate and the oil. These tests are to be exposed under constant conditions of temperature, if possible, for three weeks’ time, making weighings of each plate every day for six days and then every other day for twelve days.

(b) Another series of tests shall be made, in which 80% of raw linseed oil is to be combined with each of the above oils named. Previous to making any of the tests, there should be added to each oil, or to each combination, 5% of a drier containing lead and manganese. The drier to be used is of the standard grade submitted, together with the oil samples. The results of the tests are to be charted and submitted at the end of the tests, so that they may be compared with the results obtained by each member of the Committee.

(c) If possible, the oils and mixture of oils used in the above tests are to be ground with pure silica and painted out upon sized paper, three-coat work, the films to be stripped and tested for strength upon a paint filmometer, at two periods two months apart.”

The drying of oils to a firm surface when spread in a thin layer is accompanied by an increase in weight, due to the absorption of oxygen. The percentage of oxygen absorbed often affords a criterion of the drying of the oil under examination, and this factor, together with data regarding the appearance of the oil film, should be taken into consideration when judging the value of an oil or oil mixture. Conditions of light, air, temperature, etc., often cause great variations in the drying of oils and the percentage of oxygen absorbed, as shown by the results obtained in the following tests. Although it was impossible in these tests to have the conditions under which each experimenter worked parallel in nature, the tests afford nevertheless considerable information for guiding future work of a similar nature.

An examination of the results obtained showed generally that the greatest increase in weight occurred during the period in which the oil dried up to a firm film. This occurred in most cases within 48 hours. After this period a slight increase in weight was often noticed, and then a more or less steady decline, varying with the oil examined. Had the oil tests been continued for a greater length of time, a much greater loss might have been observed.

It was impossible to include in the tests the oil-silica film work, on account of lack of time. It is believed, however, that these tests should be conducted, as they would throw much light on the elasticity and strength given to paint films by various oils.

[8] Lost in weight throughout test.

[9]Gained in weight throughout test.

[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.

CHAPTER III

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.[12]

[12] The author gratefully acknowledges the assistance of Dr. J. A. Schaeffer in the preparation of the photomicrographs shown in this chapter.

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.

Crystals of Cerussite in Old Dutch Process White Lead. (Greatly magnified)

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.

Corrosion cylinders used for making Quick Process White Lead

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.

Sheet iron box luted at bottom with water. Atomized lead, blown into box with steam, falls to bottom and becomes hydrated (Mild Process)

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 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.

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 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.

View of Furnace for Making Sublimed White Lead

View of Goosenecks Used for Collecting Sublimed White Lead Fume

Bag Room Where Sublimed White Lead is Deposited

Photographs courtesy of Picher Lead Co.

Sublimed White Lead

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:

View of Zinc Oxide Furnaces

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.

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.

Zinc Oxide	Zinc Lead White
Zinc Lead. By transmitted light (The Pigment shows black)
Lithopone	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.

Asbestine Mine at Easton, Pa.

American Barytes. Transmitted light
(The Pigment shows black)

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].

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.