CHEAPER PAINT FOR THE NAVY.
By Naval Constructor Henry Williams, U. S. Navy.
"Everywhere the paint and shellac was of excessive thickness, in places being more than one quarter of an inch thick."—Recent report of inspection of a naval vessel.
Paint materials form one of the most important classes of naval supplies, and their use has contributed to many officers' reputations for efficiency through the aid they lend in making a "smart ship." There was at one time a general understanding in the British navy, reflected somewhat in ours, that no officer could aspire to the command of a first class man-of-war who, as executive officer of a similar ship, had not kept a "smart ship." This included the liberal and proper use of paint, provided often at the officer's own expense.
In these days military efficiency is the main consideration in estimating an officer's value and paint materials cannot be considered as affecting this, other than indirectly. On the other hand, economy is being urged on all sides, and the proper and economical use of paints generally has not been given serious consideration, at least not until recently.
In order that the importance of the subject from this point of new may be judged, the value of the purchases for the year 1910 of the more important paint materials is given:
White lead $125,000
White zinc 80,000
Red lead 50,000
Linseed oil 100,000
Japan drier 17,000
Turpentine 70,000
Shellac 135,000
Alcohol 49,000
These figures though only approximate will serve to show the relative importance from a monetary point of view of the various materials, and also justify the statement that the navy's annual bill for painting, including the cost of labor, is not far from one million dollars.
The author has had occasion frequently to discuss the subject of paint for the navy with paint manufacturers and chemists, men who are familiar with conditions as they exist in the trade. These gentlemen, with few exceptions, have stated their opinion that the navy's practice in the purchase and use of paint is extravagant and not justified by the requirements that equally good results could be obtained with much cheaper materials and good enough results could be obtained with still cheaper materials.
The paint and varnish industry has advanced more within the last ten years than it had advanced in the previous three centuries It is probable that the navy has not shared fully in the benefit due to this advance and the attitude generally adopted toward any changes in existing methods is one of conservative resistance, due frequently to lack of interest.
Ready Mixed Paints
Up to recently practically no use was made of ready mixed paints in the navy; the raw materials were issued and mixed on board ship when required for application. Early in 1911 a change was instituted by which paints mixed ready for use are issued v naval vessels in place of the raw materials. This change is in lint with commercial practice, as nearly all the large manufacturing concerns and railroads issue and indeed purchase their paints ready for application. The sale of mixed paints in the United States is said to exceed sixty million gallons annually.
It is a well established and generally admitted fact that a compound paint composed of two or more pigments is far more durable than paint made of one pigment only, and that the intelligent combination of several raw materials produces the best results. Furthermore, the mixing of paint on board ship could not be done as effectively, with no paint mixing machinery or other appliances, as in the navy yards, which have power mills and mixers of the most modern types. Another advantage, and an important one, that is offered by the issue of ready mixed paints, is the facility it affords for the use of newer paint materials, which are gaining ground commercially, and which the navy should use, if it is to avoid the deserved accusation of extravagance and of being backward in such matters. This important part of the subject will be discussed more fully in another place.
In order that a discussion of painting materials may be profitable it seems appropriate to state the characteristics and limitations of the more important of the paint materials now commonly utilized in the navy.
White Lead
This is the white pigment most generally used and it enjoys a well deserved popularity among painters. For two thousand years white lead was the only white pigment used. The process by which it is manufactured most generally, known as the old Dutch process, has been in use practically unchanged for centuries, a description of it being found in Pliny's writings. It consists essentially of a slow corrosion of buckles of metallic lead in earthenware pots which contain acetic acid and tanbark. Carbonic acid is liberated from the tanbark and acting on the lead converts it into a hydrated carbonate of lead. White lead when mixed for painting purposes combines with the linseed oil, forming an unctuous substance known as "lead soap." This accounts, in a measure, for the popularity of white lead with the practical painter, who by the feel of the paint on his brush and the ease of application readily determines whether it has been made with white lead, or with "adulterants." It is a fact generally admitted that a paint made with white lead alone is not so durable as when white zinc, or even when the so-called "fillers," such as barium sulphate, silica, or similar materials are added.
For naval purposes white lead has one serious defect in its susceptibility to the action of sulphur gases. Who on board ship has rot seen freshly applied white paint turn black, due to this cause? Generally for this reason the last coat of white paint to be applied 0 interiors of ships consists exclusively of white zinc.
White Zinc
White zinc or zinc oxide as a paint pigment is about sixty years old and in that time has gained a well deserved popularity. It is produced by heating metallic zinc in retorts until it vaporizes. In his condition it is passed into chambers where it oxidizes and falls as a white impalpable powder. One of the by-products is he zinc dust which is used in the manufacture of the Norfolk Ship-bottom Paint. White zinc is graded according to whiteness. The whitest is known as "French process" white zinc: that not so white is the "American process," which now is purchased almost exclusively for naval purposes. White zinc requires much more linseed oil to make a proper paint than does white lead. It dries with a hard brittle vitreous surface, in contrast to white lead which produces a chalky surface. Also, in further contrast white zinc is very fine and white lead is rather coarse, so that in mixtures the interstices between the white lead particles are filled in by those of the white zinc. Owing to the different effects of the two pigments, mixtures of them are very popular in paints, and in the navy are generally used. Paints made with a mixture of the two pigments undoubtedly are more efficient than those made with either one alone. Similarly white zinc is mixed profitably with barium sulphate, silica, or other like substances and paints made from these ingredients have been used recently in the navy with good results.
Zinc oxide requires a far greater proportion of linseed of to make paint than does white lead, and this consideration must not be lost sight of in view of the prevailing high cost of linseed oil.
Red Lead
Red lead is the oldest of the protective paint pigments and in this respect it is analogous to white lead. For many years a better paint for the purpose was known and at the present time is used very extensively and well thought of, especially among sea-going men. It is made from metallic lead by heating, first to produce litharge (PbO), and then to produce red lead or orange mineral (Pb3O4). When mixed with linseed oil to make paint 4 acts very much like plaster of paris or cement when mixed with water. The red lead gives off sufficient oxygen to harden the linseed oil and the paint becomes hard and unfit for use. For this reason no pure red lead paints come ready for use. By the admixture of china clay, silica, or similar inert pigments, this hardening action is prevented. A very satisfactory red lead paint is made with the following ingredients:
65 lbs. dry red lead.
10 lbs. dry silica.
10 lbs. dry china clay.
1 lb. drier.
1 lb. turpentine substitute.
20 lbs. linseed oil, raw.
Paint made in this way is probably more efficient than if made with red lead only and will keep without hardening.
Red lead is used on board ship for many purposes for which it is absolutely unsuited and where paint costing less than half as much would give better service. These locations are coal bunkers, double bottoms, trimming tanks, and bilges. The difficulty that is encountered on the average ship in keeping the metal on these locations painted furnishes abundant proof that red lead is not suitable. It is a safe rule to follow that red lead is efficacious only for use as a priming coat, where other kinds of paint are applied over it and in locations where the metal can be rendered absolutely dry before painting. This refers especially to moisture that condenses on the metal in such spaces as double bottoms. Red lead is acted on with ease by sulphur gases when unprotected by another paint. It requires about 33 pounds of red lead to mix with a gallon of linseed oil, so that the cost per gallon of red lead paint is something over $2.00. It is difficult to get painters to apply it properly, due to its weight and the fatigue resulting from handling the paint brush heavy with paint. For that reason there is a tendency to dilute it unduly. Some grades of red lead are coarse and crystalline, and are not so efficient as the finely divided varieties. For this reason one of the laboratory tests is an examination of red lead under the microscope in comparison with a standard sample.
Shellac
The United States navy is probably the largest single consumer of shellac, of which about half a million pounds are purchased annually and used largely to make varnish for linoleum covered decks of ships. Recently considerable quantities have been used in making ship's bottom paint.
Shellac gum, unlike other varnish gums, is not a fossil but is an annual crop. It is obtained from the secretion of innumerable small bugs which feed on the leaves of a bush growing in India and Siam. The secretion, which hardens, is called "stick-lac" and is collected by natives who take it to the factories, where it is ground, sifted, washed and winnowed and afterwards heated and spread into thin sheets to form the gum shellac of commerce, it is adulterated frequently with ordinary rosin, of which large quantities are shipped to India for the purpose.
As noted above the principal use to which shellac is put in the navy is the manufacture of varnish for linoleum covered decks. For this purpose it is dissolved in alcohol and a pigment, either Venetian red or yellow ochre, added to give it color and some body. On the average ship large areas of linoleum are "shellacked" each week. In spite of arguments that have been advanced that this course is necessary for sanitary reasons, there seems to be no reasonable doubt that it is mainly for appearance sake. Consideration leads to the conclusion that the cost of this luxury, which goes annually over $75,000, is hardly justified, and when the deleterious effect on the linoleum that must be exerted by the alcohol in the shellac is considered, it is a matter of wonder that the custom has continued to prevail so long. Linoleum consists of ground cork held together by a binder of oxidized linseed oil and varnish gums. A small piece of linoleum soaked in alcohol over night shows clearly the effect of the alcohol in dissolving the binder, leaving the ground cork without cohesion. The cost of providing and fitting linoleum to the decks is about $1.50 per square yard, as much as the average householder pays for his carpets. Other materials, such as ordinary floor wax, could be used for polishing the surface of the linoleum and the requirement for appearance could be met at much less cost than at present, without sacrificing to any extent the much abused consideration of "sanitary conditions."
Linseed Oil
Linseed oil was the only oil medium for paint for many years, and is the only one at the present time used in the navy. It is made by expressing the seeds of the flax plant, after they have been ground and heated. It has the property of combining with oxygen and, when applied in a film, of hardening into a tough covering for the surface to which applied. When heated to a temperature of 3000 F. to 500° F., it acquires an added facility for oxidizing or drying. This is boiled linseed oil. Very much the same effect is obtained by adding so-called driers, made usually with the oxides of lead and manganese. These supply oxygen to the oil, which in turn they regain from the air. Such boiled linseed oil is called "Bunghole" oil, and is the boiled oil of commerce. Boiled linseed oil has a decided advantage for use in closed spaces on ships due to its facility of drying. It is not issued generally to ships of the navy, the required effect being obtained through the use of driers in the paint.
Due to an unprecedented condition in the linseed oil market the price has tripled in recent years. The paint industry is the only one that adheres to the use of linseed oil, although there are substitutes that promise well and undoubtedly can be developed to take its place in part if not entirely. The most important of these substitutes is fish oil, which is made from menhaden and now can be produced without the disagreeable odor that marked it formerly, at about half the price of linseed oil. Experiments made with fish oil for paints for naval purposes promise well and its use to a certain extent is likely.
There is no justification for the disposition of many to consider fish oil or similar materials as adulterants, and many manufacturers of oil cloths, patent leathers and imitation rubber fabrics have found that, when properly treated, it is superior to linseed oil. It can be treated so as to withstand the action of high heat and for this reason is valuable for smokestack paint. Dr. Maximilian Toch is authority for the statement that the addition of fish oil with suitable drier renders paint more durable to sea air and corrects the chalking tendency of white lead and the hard drying quality of white zinc.
It is probable that fish oil and other oils are destined to supplant to a considerable extent linseed oil for painting, as the conditions that have led up to the scarcity and consequent high price of flax seed are not likely to be relieved.
China wood oil, or Tung oil as it is called also, can not be regarded as a substitute for linseed oil, except for certain special uses. Linseed oil films have not the property of excluding moisture and for that reason linseed oil paints will not stand well in damp locations. Paints made with Tung oil have the quality of being water-proof and its use in damp-proof paints is general for that reason. Tung oil is difficult of manipulation and to obtain Rood results considerable skill is necessary. In spite of this, however, its use is becoming general, not only in paint above mentioned, but also in varnishes. Dr. Toch is authority for the statement that a better varnish can be made out of Tung oil and rosin than out of higher grade gums and linseed oil.
Soya bean oil and corn oil are used for mixing with linseed oil. It has been stated on good authority that as much as 20 per cent of them can be mixed with linseed oil without affecting the properties of the latter, except as to drying.
Turpentine
Turpentine has been used for many generations as a solvent for paints and varnishes. It is manufactured from the sap of several species of pine trees, by distilling with steam. Due to the destructive methods employed in gathering turpentine the supply has decreased enormously in recent years, and the price has increased correspondingly. Unless these methods are interfered with, it is likely that in the lifetime of the present generation turpentine will become a chemical curiosity. It is used to mix with paints as a diluent or extender, its function is mechanical, being simply to increase the spreading power and working quality of the paint. It evaporates leaving no residue, so it cannot be said that it contributes except indirectly to the life or quality of the paint film. It is generally admitted now that entirely too much stress is laid upon the value of turpentine as a paint vehicle, and when this is realized, substitutes will be used that serve the purpose quite as well and in many cases better than turpentine itself.
Due to the scarcity of sap turpentine, of recent years so-called wood turpentine has been manufactured extensively. This is made by the distillation in retorts of sawdust, shavings, old logs and roots of pine trees. The quality of these turpentines depend upon the method and care used in their manufacture, many of them being the equals in every respect, except possibly as to odor. of the sap turpentine. Others have very disagreeable odors and injurious properties due to the products formed in the destructive distillation of the wood. For exterior painting these wood turpentines generally are quite as efficient as the sap turpentine. For interior painting their odor in most cases condemns them. In general they cannot be said to have any advantage over benzine products, which are supplied for the same purposes.
The navy department purchased in the year 1910 about 75,000 gallons of turpentine under specifications that required deliver, of the highest grade of sap turpentine that it is possible to obtain, and consequently at prices somewhat higher than the market This turpentine was used by the navy for paints of the sort in which manufacturers of ready mixed paints would not consider using other than benzine products as solvents. Consideration of these facts led to the decision early in 1911 to discontinue the purchase of sap turpentines except for special purposes and t purchase for general use in paints a turpentine substitute which had been shown by test to meet all practical requirements. This material is a petroleum product similar to benzine, but with higher flash point. It evaporates at a temperature of 212° F. with no residue. The use of the material has met with some opposition in the navy, reports have been submitted as to its unsatisfactory qualities. It should be borne in mind, however, that it is a commercial product used very extensively commercially for the same purposes as the navy uses it, and any failure consequently should be considered rather as the fault of the persons using it than of the material. It is likely also that failures due to other causes are attributed to the use of the turpentine substitute. A conservative estimate of the saving to the navy resulting from the use of turpentine substitute is $30,000 annually. One of the objections advanced frequently and with effect against petroleum thinners is the belief that they have a tendency to cause white paints to turn yellow. That this is true is doubtful. The author has never been able to understand that very white paint should be necessary on board ship, and in discussing the matter with expert house decorators finds that from artistic considerations they favor a cream or light yellow rather than dead white. This tint permits the use of more suitable varnish in the gloss paint, as will be pointed out further along.
Iron Oxide Paints
Large quantities of Venetian red are purchased in the navy for coloring the shellac varnish used on linoleum decks. It consists largely of calcium sulphate or gypsum, the remainder being about 30 per cent of iron oxide. One of the most durable of the proprietary metal paints tested at the Brooklyn Navy Yard has a pigment consisting of Venetian red.
Indian red is a natural oxide of iron, practically pure, and is used as a coloring matter in the Norfolk anti-fouling ship-bottom paint, in order that it may be distinguished readily from the anticorrosive.
Metallic brown is another oxide of iron—the best grades being the natural ones. It is used very extensively commercially on steel with success and is considered to be one of the standard protective paints, many persons thinking it the equal of red lead for this purpose.
Black Paints
There are many forms of black paint pigments, all of them practically pure carbon, though they differ in structure and qualities. The one most commonly used in the navy is lamp-black, which is made by the combustion of oils. It has remarkable tinting strength and the outside paint now used on ships owes its slate color to the addition of lamp-black, the base being of practically the same constituents as the white paint used formerly.
There are a number of graphite pigments, all of them being nearly pure carbon; alone they form an unsatisfactory paint pigment, but added to other heavier bases graphite pigments have great merit.
Red Paints
For many years quantities of English vermilion paint were used on naval vessels for painting the inside of ventilator cowls. There is no doubt that this added considerably to the smart appearance of the ships in contrast to the white hulls and salmon-colored top sides.
English vermilion is a sulphide of mercury and has the defect of hardening when mixed with oil and kept. The purchase of English vermilion for the navy was abandoned a number of years ago, in line with commercial practice, in favor of the so-called artificial vermilion. This is cheaper, less likely to change color and can be kept mixed ready for use. The particular pigment used in the navy is a lead-barium lake of the azo dye, known commercially as "Lithol."
Red, as well as green, yellow and blue paints, do not have the same importance in the navy as was the case formerly, due to the adoption of the slate color for exteriors of ships. Their use is confined almost exclusively to painting the distinguishing striping on piping on board ships.
Bitumastic Paints
Specifications for recent battleships require that the builders, in lieu of the red lead and other paints usually required for these localities, shall apply to coal bunkers, trimming tanks, reserve-feed water tanks, inner bottoms in machinery spaces, and bulkheads and foundations in machinery spaces to height of floor plates, the so-called bitumastic paints or their equivalents. These materials are supplied by several firms under different names, all of them being of similar composition and characteristics. A discussion of them seems proper, as they promise to play an important part in future painting of the spaces mentioned above, which in the past on naval vessels have been a source of considerable worry to the officer responsible for their up-keep. Coal-tar products deteriorate when exposed to light and for that reason these materials can be applied only in confined spaces. Formulas are given for their manufacture which have been determined tentatively and, while they should not be regarded as final, they will serve to indicate the character and general ingredients of the materials.
The first coat to be applied in all cases is the so-called "solution," which may be made by melting 100 lbs. of coal-tar pitch and 50 lbs. of Trinidad asphalt. When liquid the mixture is removed from the fire and cooled and thinners added consisting of 65 lbs. of coal-tar naphtha and 15 lbs. of mineral oil.
The "enamel" may be made by melting 350 lbs. of coal-tar pitch and 350 lbs. of Trinidad asphalt together and boiling for about three hours.
The "cement" may be made by melting 150 lbs. of coal-tar pitch and 120 lbs. of Trinidad asphalt together and boiling for about three hours, when 150 lbs. of Portland cement is added and stirred in.
In all of these care is required in the heating, the quality of the material is dependent entirely on the manner in which this is accomplished.
The "solution" is applied first in all cases and does not require to be heated, but is brushed on cold. In some spaces the other materials are unnecessary, though it is best generally to follow up the solution with the enamel or cement, both of which must be heated to apply. The former goes on in thickness of about 1/16", the latter about ½". The cement is applied only to the bilges in the machinery spaces, and in the fire-rooms frequently it is protected by a covering of Portland cement.
These materials have been tried to a limited extent on naval vessels, but have been used extensively on merchant ships for many years. The author inspected, in 1904, the American Line St. Louis, which had had the bitumastic materials applied at the time of building in 1894-1895 to trimming tanks, chain lockers, double bottoms, coal bunkers and inner bottoms. The original material was in good condition and had received only minor repairs. The metal underneath generally showed no signs of corrosion and in many cases the hammer marks around rivet heads could be seen when the bitumastic was removed.
The So-Called "Inert Fillers"
For many years white lead, white zinc, linseed oil and turpentine have been regarded as the standard ingredients of which any paint should be made. Many manufacturers quietly utilized other materials that gave results quite as good, but the consuming public cared mainly about the results and had no means of determining the ingredients. A general tendency grew up to regard as adulterants many other pigments than the above that have excellent qualities to recommend them as paint ingredients. Among these may be mentioned lithopone, blanc fixe, barytes, whiting, gypsum, china clay and silica. Some years ago a number of states passed the "pure paint laws" that required, in effect, labeling packages of paint with a statement of the contents. This precipitated the situation, in which many manufactures find themselves, of being forced to justify their use of materials that have given satisfactory results, but which they have used unheralded and which they have permitted the public to be taught to consider as adulterants. An effective campaign now is being waged to show that all of these materials have their function when used in the proper proportions in paints, though their unskilled use perhaps may not give as satisfactory results as older and better known pigments. It was demonstrated by actual exposure tests at the seashore that paint in which the much-despised barytes was a principal pigment gave as good results as one made up with only white lead and white zinc. Many of the numerous kinds of paints used by the agricultural implement trade are made largely from barytes and the results obtained from these should be a sufficient lesson to the navy that its paint money could be spent to better advantage than in the exclusive purchase of lead and zinc paints.
Lithopone is a remarkably fine white pigment consisting of about 70% of barium sulphate and 30% of zinc sulphide. It has achieved great vogue recently for use in the flat wall finishes, which promise to supplant wall paper to a large extent, due to their sanitary properties and durability. It is not suitable, however, for outside paint.
Blanc fixe is barium sulphate artificially produced and is superior to barytes in its fineness and texture. It has many qualities to recommend it for naval purposes and experiments looking to its use have been undertaken, with excellent practical results. Slate color paint for outside of ships made according to the following formula has given excellent results in preliminary tests:
450 lbs. blanc fixe, dry.
70 lbs. French ochre, dry.
467 lbs. white zinc, dry.
93 lbs. graphite in oil.
3 lbs. lamp black in oil.
93 gal. raw linseed oil.
12 gal. oil drier.
8 ¾ gal. turpentine substitute.
2 gal. benzine.
Barytes is well known as the white mineral barium sulphate. Used alone it has little covering power, but when mixed with white zinc or white lead it gives excellent results. Consideration shows that it would not be unreasonable to expect it to show durability as a paint pigment, as it is one of the most permanent of the minerals and is absolutely insoluble in most solvents. Due to its density and crystalline structure, barytes has not large covering or hiding power, and needs to be mixed with other pigments to form satisfactory paint.
Whiting, or calcium carbonate, is used mainly for making putty, but small percentages are used by many manufacturers in all paints for the purpose of neutralizing any acidity that may develop. This feature of whiting recommends it highly for paints for steel surfaces.
Gypsum, or calcium sulphate, is the main ingredient of Venetian red, of which large quantities are used by the navy; the remainder being ferric oxide. In its pure state it is used to advantage if free from lime.
China clay is used mainly as a filler for paper, but has considerable value in paint mixtures, its addition being an improvement to red-lead paint as seen above.
Silica is useful in mixing with other pigments, largely because of its quality of presenting an excellent surface for repainting. This quality alone should recommend it for use in many of the paints used on ship-board, and the statement has been made that the time is not far distant when all good mixed paints will contain silica.
Asbestine is a silicate of magnesium, and is fibrous in character. It is extremely stable and when used in mixed paints has a tendency to hold up the heavier pigments and to keep them from settling to the bottom of the container. It is used considerably in ready-mixed paints for this reason.
Varnishes
Varnishes are made ordinarily by melting the gums or resins, then adding hot linseed oil and, when the mixture has cooled sufficiently, thinning with turpentine or petroleum spirits. The vanishes intended for outside use, usually known as "spar varnishes," are made with better and harder gums and do not contain so much volatile solvent and consequently dry more slowly. Varnishes for interior use are usually not so expensive, have mort volatile solvent and dry much more rapidly even in confined space.
Considerable skill is required in the manufacture of varnish and the results vary considerably between the products of different makers, even when the same materials have been used. Some makers, by the use of lower-grade gums and even common pine rosin, can produce better varnishes than their competitors cat with the best materials. The only test of varnish that can be relied on is a service test, which, however, is prohibited by the length of time required before the varnish will wear out It is. therefore, necessary to purchase varnish on specifications which require a chemical test only, and, though this cannot be regarded as showing conclusively the quality of a varnish, it is fair generally to assume that varnishes in which only the best materials have been used are of good quality and will give satisfactory results.
Damar varnish, which is made from damar gum and turpentine without the use of oil, is used in mixing enamel paints for interior; of living spaces on ship-board. It was selected for this purpose clue to its light color, although it is not so durable as the linseed oil varnishes. With a slight sacrifice of whiteness, a gloss paint could be made by using an oil varnish that would be much more durable than damar varnish paint and cost no more. The flat-wall finishes made from lithopone that have become popular recently, contain a small percentage of varnish and for that reason will stand scrubbing quite as well as gloss paint made with damar varnish.
Asphaltum varnish is made in the same way as other oil varnishes by using a fossil asphalt, known as gilsonite, with linseed oil and a solvent. This kind of varnish has not very great durability.
Varnish gums or resins are fossil remains of exudations from trees and there are many varieties and grades. The older gums are harder, amber being the final result of aging. Varnish has been made with amber, but, due to the extreme heat necessary to melt it, the resulting varnish was dark colored and had no particular merit.
Special Rust-Preventing Paints
The subject of corrosion of steel has received of late years considerable attention commercially, due to the amount of money being invested in buildings which depend for their existence upon the integrity of their steel structures. This steel is not subjected to the trying conditions that a sea-going ship experiences, for the reason that it is imbedded usually in cement concrete, and, moreover, is not exposed to salt water or air laden with salt moisture.
As a result of these efforts there have been developed a number of paints designed especially to prevent rusting of steel surfaces. While it would not be possible to discuss all of the different kinds and characters of these paints, it is believed that description of several of them, that have been used successfully to some extent in the navy, will be of interest in showing the possibilities and the breadth of the field.
A paint that has been used extensively in steel work of recent buildings contains as a pigment a mixture of oxides of silica, calcium and aluminum, resembling closely Portland cement, which is mixed with other materials and china wood oil. The latter has the property of forming a moisture-excluding film, while the cement absorbs, when applied, moisture that may be present on the surface and permits the use of such a paint on moist surfaces. These latter characteristics are sufficient to justify the substitution of such a paint for many localities in which red lead now is used. Its price, which is one-third less than that of red lead, and its protective and rust-preventing qualities, which have been shown by experiment to equal if not surpass red lead, are added reasons in favor of the adoption of such a paint for naval vessels.
A paint that has given excellent results when used on the interiors of trimming tanks of submarines is made with a graphite pigment and an asphaltic oil thinned with benzine. This paint has displayed remarkable protective qualities when used under the trying conditions mentioned above and its cost is less than one dollar a gallon. Red lead, which costs not far from two dollars a gallon, though used generally for the purposes mentioned, does not give results that are even reasonably satisfactory, due to the fact that linseed oil films do not exclude water, and red-lead paint made with linseed oil will not adhere properly to a surface that has the slightest trace of moisture.
Another paint that has been tested extensively at the Brooklyn Navy Yard, for uses to which red lead has been put, is composed of a pigment similar to Venetian red, containing iron oxide, calcium sulphate and silica, and of specially high quality of linseed oil, turpentine and driers. The merit of this paint appears to be due to the special quality of the linseed oil and the care used in manufacture, and, though it is somewhat more expensive than the others mentioned, the paint is much cheaper than red lead and appears to be more effective.
Conclusions
An important consideration, and one that should not be lost sight of in connection with the paint situation in the navy, is the fact that rarely is paint allowed to live its full life, or the paint film to perish through the action of the elements. Occasionally in inaccessible places on ship-board the metal becomes badly corroded, either under paint, or else due to its absence. These cases are unimportant and can be attributed generally to the unsuitability of the paint used. Most of the paint, however, that is used on ships is painted over before it has perished. Ample proof of this is the thickness of the paint on various parts of old ships, and the scaling of old paint that goes on continually on men-of-war. Granting, for the sake of argument, that the new paint materials, such as turpentine substitutes, linseed oil substitutes, the inert fillers, etc., have not the durability of the materials heretofore used, it would even then be reasonable to use them. When a house on shore is painted, the owner expects the paint to last at least two years and would not consider cheaper materials if he felt that it would shorten the life of the paint appreciably. The labor cost of painting it too high. He does not expect to repaint until the paint film has disintegrated and the wood or metal begins to show through. Ships are repainted, however, for other reasons, and it is rare that any part of the ship that is visible goes more than one year without repainting, most of it being painted three of four times a year.
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