Henry A. Gardner

“ Everyone knows, of course, that oil and water do not readily mix and are, in fact, more or less repellent to each other. It is, however, true that, in spite of this, oils can [224] carry quite a percentage of water, without the admixture being apparent to the eye. In addition to this, careful experiments have proved very conclusively that linseed oil films, even after they have oxidized and hardened, have the power to a certain extent of absorbing water from the atmosphere. It is, therefore, safe to say that no linseed oil film in a paint coating is dry all the time. ”

“ A coating of linseed oil alone is not only weak, but the simplest and crudest experiments will show its porosity and this porosity increases rapidly with progressive oxidation, the porosity of course definitely hastening the over-oxidation or chalking. In proportion, therefore, to our success in filling the voids in the linseed oil film with proper pigment materials, we will in that degree succeed in excluding agencies of decay, not only from the mass of the paint coating itself, but also from the surface to be protected. ”

“ 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. ”

“ 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 [14] very soft film, and the use of hard driers, such as the metallic tungates, is therefore advisable with menhaden oil. ”

“ 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 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. ”

“ 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. ”

“ It is well known that various pigments when ground in oil differ in their hiding power in direct proportion to the difference in the refractive indices of the pigments and oils used, those containing high percentages of pigments such as white lead and zinc oxide being superior in hiding power. After the second and third coat of paint had been applied to each panel, there was evident a remarkable difference in the hiding power, as the black cross showed through in some cases quite clearly, while in other cases it was almost completely hidden. ”

“ The enormous development of bacteria in the bouillon, treated with the washings from the wall-papered surface, was sufficient evidence to convince one of the greater sanitary value of the wall paint, the washings from which gave a culture practically free from bacteria. The colonies of bacteria shown in the petri-dish test made of the washings from wall paper further supports these findings. It will be noticed that the tests made from the washings of the wall paint show practical absence of bacteria, and was clear, as was the bouillon-solution test of the paint. ”

“ The modern grinder has accepted the Law of Minimum Voids, and upon this law he bases the design of paint formulæ, aiming toward the production of what have been properly termed Scientifically Prepared Paints. Perry’s formulation of the Law of Minimum Voids in a paint coating, and the analogy which he has drawn between a scientifically prepared paint and a well-proportioned concrete, was the result of genuine scientific thought following observation and experimentation. ”

“ The dried vehicle, linoxin, is notable for its elasticity, and it is weak in crushing and tensile strength, and in hardness or resistance to surface wear. The fact that it is a semi-solid furnishes an opportunity to modify and improve those characteristics of a solid in which it is deficient. The semi-solid, rubber-like linoxin between the coarser particles of the pigment obviously uses these coarser particles as supporting points. The medium sized particles of the second group of alteration products serve the same purpose as the broken rock in concrete. ”

“ The hiding power of a paint is one of the properties which the master painter looks upon as most essential, but it should, of course, be accompanied in a satisfactory paint by good spreading power and longevity.
Actinic Light Tests. After the drying of all the paints, it was decided that it would be of extreme interest to conduct a test on the resistance of certain paints to actinic light. It is well known that the ultraviolet or chemical rays of the sun are most energetic in causing chemical reactions that result in the early decay of certain types of paint. ”

“ Preparation of Paint Films. The study of paint films is one that has become of vital importance, and is receiving at the present time great attention. Among the many methods which have been suggested and attempted for securing paint films, a few already well known may be mentioned.
By painting upon zinc and eating away the zinc with acid: The objection to this method is very evident, namely, the action of the acid upon the paint coating, which is likely to be very severe. Another method has been to spread paraffin on a glass plate, and painting upon this surface. ”

“ From these tests, the inspectors reached the unanimous conclusion that a paint made from any mixture of more than one white opaque pigment, either when used alone or in combination with small percentages of inert pigments, is far superior to any one single pigment paint. It was found that the straight white lead paints failed in every case, and this failure was so marked as to make it a conclusive demonstration of the unfitness of white lead along the Atlantic coast, when used without other pigments. Paints made with large percentages of white lead, however, gave excellent results. ”

“ These are two vital qualities in a paint, as it is through its strength that a paint resists abrasion, cracking, peeling, and blistering. That elasticity is a vital qualification [81] of a paint may easily be seen through the checking of oil paintings, which, as Ostwalt has pointed out, is due to the unequal coefficients of expansion between the ground and the paint. This is particularly noticeable in the alligatoring of many enamels which contain large percentages of zinc. ”

“ The success of certain European countries in using lithopone as a pigment, even in a very high percentage, may be due to the use of a special vehicle, and, if it is found in future tests that this material, which has been reported as well suited in Northern European climates, may be benefited and made of service by the addition of special oils and special vehicles, then this test would be of great value to the whole paint trade at large. ”

“ By placing small, brightly polished steel plates into a mush of paint pigment and water, a determination may be made of the pigment’s effect upon the metal. Some pigments, under such conditions, cause rapid corrosion of the steel plates. Such pigments are stimulators of corrosion, on account of acid impurities which they contain, or because of their effect in stimulating galvanic currents. Many carbonaceous pigments are of this type. Other pigments have the effect of keeping bright the steel plates and preventing rust. ”

“ The use of cypress, pitch pine, and other faulty woods, is often the cause of the failure of a paint, which on good wood would show up well. For this reason, only the white pine panels painted with white paints were considered in the inspection, the yellow pine panels and cypress panels having been thrown out of the test at last year’s inspection. ”

“ There seems to be no question, however, that the use of wall paper is steadily decreasing, and that the art of interior decoration is undergoing a transition to the almost universal use of paint.
Modern progress demands the maintenance of sanitary conditions for the benefit of the public welfare, and there is no doubt that from the standpoint of sanitation and hygiene, properly painted wall surfaces are far superior to papered walls. There is an abundance of evidence which shows that dust germs may easily be harbored, and thus disease transmitted from wall paper. ”

“ Although the laboratory accelerated tests for the determination of the relative value of structural steel paints afford information of some import, there seems to be a general opinion that the best method to follow, if information of a reliable character is to be obtained, is to make actual field exposure tests upon large surfaces. The results of the above described water-pigment tests suggested the erection of a series of steel panels on which to test out the same pigments under practical service conditions. ”

“ 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. ”

“ With the aid of high-power magnifying glasses, checking was determined. The degree of chalking exhibited by the various paints was ascertained by rubbing a piece of black cloth across the surface of each paint. Close observance was made to determine scaling, peeling, cracking, gloss, color, and the other factors to be considered when examining a painted surface. From these observations it was possible for the inspectors to state whether a panel exhibited general good condition, general fair condition, or general poor condition. ”

“ 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. ”

“ The adhesion of the linoxin to the coarse group of particles and to the underlying material is vital to the life of the paint coating. If the coating parts from the surface beneath, we have scaling or peeling. It is universally admitted that this will result from use of zinc oxide as the sole pigment. ”

“ Failure of the tests, however, in nearly every case except where zinc oxide and whiting were mixed with the lithopone, indicated that pigments such as zinc and whiting are necessary in order to prevent the decomposition of lithopone pigment paints. The decay of lithopone paints after they are applied seems to start with rapid oxidation of the linseed oil, and this oxidation seems to continue in a progressive and even accelerated way; after six months’ exposure the surface of the paint being chalked to a great extent and showing rapid decomposition of the binder or vehicle. ”

“ It seems to be a curious fact that the more quickly a product or an article is fashioned by man, the more quickly it tends to return again to its original oxidized condition. Some manufacturers of steel, however, through an understanding of the causes of rust, have progressed in the manufacture of slow rusting materials, either by the elimination, or by the proper distribution of impurities. ”