CHAPTER XVI
STRUCTURAL STEEL PAINT TESTS
=The Necessity of Protective Coatings.= Most painters have in the past considered of minor importance the painting of iron and steel; any paint that would properly hide the surface of the metal being accepted without much question. The demand, however, for structural steel for office buildings, factories, steel cars, railroad equipment, etc., has doubled the output of structural paints, and created a demand for painters having a knowledge of the proper materials to use in the painting of steel, so that its life may be preserved, and its strength maintained. Such knowledge is as important to the painter as a knowledge of how to properly select materials for the painting of wood, and how to temper these materials to suit the various conditions met with.
=The Cause of Rust.= Everyone is familiar with the appearance of rust, but few actually understand what causes rust. No attempt will be made here to present even an outline of the many theories advanced to explain the phenomenon of the rusting of iron, for the subject is as diverse as it is interesting. A brief résumé, however, will be given of the now generally accepted theory that explains the subject. This theory is called the electrolytic theory. "Auto-electrolysis" is the term used to define the peculiar tendency of iron to be transformed from a metal possessing a hard lustrous surface, high tensile strength, and other useful properties, to a crumbling oxide that falls to the ground and again becomes part of the earth from which it was originally taken by man.
This "going back to nature" is more readily accomplished by most of the steel produced to-day than by the old hand-made irons produced many years ago. 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.
When iron is brought into contact with moisture, currents of electricity flow over the surface of the iron between points that are relatively pure and points that contain impurities. These currents stimulate the natural tendency of the iron to go into solution, and the solution proceeds with vigor at the positive points. The air which the water contains oxidizes the iron which has gone into solution, and precipitates the familiar brown iron rust. Thus water, which acts as an acid, and air, which acts as an oxidizer, have combined together to accomplish the downfall of the metal.
=Inhibition and Stimulation of Rust.= It is obvious that if means could be devised to stop the solution pressure of iron and make it resistant to the flow of surface electric currents, rust could be prevented. Such methods have been devised, and to better illustrate how they operate, an analogy may be drawn between iron in water and shellac in alcohol.
It is common knowledge that when shellac is placed in alcohol, the shellac will force itself into solution in the alcohol, and form a clear, transparent lacquer. If, however, there should be mixed with the alcohol a quantity of water, it would be found that the shellac could no longer go into solution, and it would remain in its original condition. In the same way, if there be placed in water a small quantity of material, such as soluble chromates, or an alkaline substance like caustic soda or lime, it will be found that iron will no longer have a tendency to go into solution in this treated water, but will stay bright and clean. These materials which prevent the rusting of iron have been called by Cushman, who first advanced these explanations, "rust inhibitors," or materials which inhibit rusting. The paint maker, realizing the importance of these rust inhibitors, is incorporating them into paints designed for the protection of iron and steel, and the success which paints of this type have met with from a practical standpoint is a justification of what was first called the "electrolytic theory," which suggested their use.
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. Such pigments are of the inhibitive type, and their action is to check or retard the solution pressure of the iron.
=The Effects of Moisture.= It might occur to the reader that although paint pigments, when mixed up with water and brought into contact with the surface of steel, might show either an inhibitive or stimulative action, that it is by no means certain that the same tendency will be exhibited by pigments when they are properly mixed with linseed oil and laid out as a film upon the surface of steel. In answer to this, it may be well to state that almost no material used by mankind is absolutely dry. Linseed oil, as it is pressed from the seed, comes from the cells, carrying with it a certain small definite percentage of water, and it is quite certain that even the best linseed oil that goes into use is not theoretically dry. 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 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. As a matter of fact, there is abundant evidence to show that in rainy weather, and, in fact, when the humidity in the air is high, paint films have absorbed water. As the sun comes out and warms the paint coating, and the humidity content of the atmosphere falls, this water to a large extent evaporates out of the film, only to be taken up again when the weather conditions change. This action may be likened to a breathing of the paint film, that is to say, an indrawing of water under humid conditions, followed by an exhaling of water under dry conditions. With these facts in mind, it must be apparent that pigments laid out in intimate contact with the surface of steel are subjected at all times either more or less to the reactions produced by water contact. Furthermore, as it is a property of water to become saturated with the gases of the atmosphere, such as oxygen, carbonic and sulphurous acids, and other impurities, there is present in a protective paint film at all times the elements necessary to carry on the corrosive process and reactions.
An outline of Cushman's original research work, upon which has been based the classification of pigments as inhibitors, stimulators, and inerts, is clearly presented in his report[38] as Chairman of Committee U of the American Society for Testing Materials, of which the following is an excerpt:
[38] Page 73, 1910 Proceedings of the American Society for Testing Materials.
"Three years ago the suggestion was made in a paper presented before the Tenth Annual Meeting of this Society that the various types of substances used as pigments in protective coatings might exert a stimulative or an inhibitive action on the rate and tendency to corrosion of the underlying metal. It was further suggested on a theoretical ground that slightly soluble chromates should exert a protective action when employed as pigments by maintaining the surface of the iron in a passive condition in case water and oxygen penetrated the paint film. In view also of the well-known fact that alkalies inhibit while acids stimulate the corrosion of iron, it was suggested that the action of more or less pure pigments on iron in the presence of water should be thoroughly investigated. Two years ago this Committee invited the co-operation of Committee D-1 (then known as Committee E) in the investigation, and a special sub-committee representing the two main committees was appointed.
"The methods and results of the water-pigment tests have previously been reported and published, and need not be given in detail. Briefly, the method consisted in immersing samples of steel in water suspensions of the various pigments and blowing air through the containers for definite periods of time, the corrosion being measured by the loss in weight sustained by the test pieces. About fifty pigments which are in more or less common use for painting steel were purchased in the open market and distributed among a number of the members of the Committee, who agreed to carry out the work. Each investigator worked independently of the others, except that the same general method was followed; the time of exposure to the corroding action, however, varied in the different experiments. When the results were compared and analyzed by the sub-committee, it was felt that the general agreement of the results obtained by the several investigators was striking and merited further and more systematic work. As a result of these tests the sub-committee tentatively divided the pigments into inhibitors, stimulators, and indeterminates. The word 'indeterminate' was selected after considerable discussion, because the words 'neutral' or 'inert' already possess a special meaning as applied to paint technology. The Committee takes this occasion to emphatically state that in adopting this tentative classification, the words 'inhibitive' and 'stimulative' as used by them up to the present time apply only to the results obtained in the water tests, and the inference that the results obtained have decided which class the pigment will fall into when made into a paint with the usual vehicles and used as a protective coating on iron and steel, is not justified. In order to make this point quite clear, it has been agreed by the Committee to qualify the classification so as to speak of the various materials tested as 'water stimulative' or 'water inhibitive.'"
=Importance of Field Tests.= 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. The Paint Manufacturers' Association of the United States erected and painted the panels, the work being under the constant supervision of the writer, and the inspection of the work under Committee U of the American Society for Testing Materials. A brief résumé of the work[39] is herewith presented.
[39] Page 181, "Corrosion and Preservation of Iron and Steel"--Cushman and Gardner--McGraw-Hill Book Co., New York City.
=Pickling and Preparation of Plates.= The three types of metal[40] selected for the test were rolled to billets, the middle of which were selected, and worked up into plates 24 inches wide, 36 inches high, and 1/8 inch in diameter--approximately 11 gauge. A number of plates of each of the metals selected, in all 450, were pickled in 10% sulphuric acid, kept at 180 to 200 degrees Fahrenheit, in order to remove the mill-scale. The plates were then washed in water, and later in 10% solution of caustic soda. Finally the plates were again washed in water and wiped dry. They were then packed in boxes containing dry lime, in order to prevent superficial corrosion. By this method the plates were secured in perfect condition, the surfaces being smooth and free from scale. Upon these pickled plates paints were applied with a definite spreading rate of 900 square feet per gallon. The unpickled plates, coated with mill-scale, were painted with the same paints, but without adopting any special spreading rate, thus following more closely the ordinary method of painting structural steel. A few extra plates of special Bessemer steel and Swedish charcoal iron were also included in the test, some of which were painted, while others were exposed without any protective coating. Plates of the three types of metal already mentioned were also exposed unpainted, both in the black and pickled condition.
[40] Bessemer Steel, Open Hearth Steel, and Pure Iron.
=Fence Erection and Preparation for Work.= The fences which were erected for the holding of the plates were constructed of yellow pine, the posts being set deeply in the ground and properly braced. The framework of the fence was open, with a ledge upon the lateral girders, upon which the plates might rest, and to which the plates were secured by the use of steel buttons. After the framework had been erected, painted, and made ready for the placement of the panels, a small shed was built upon the ground, and the materials for the field test placed therein. The steel plates were unpacked from the boxes in which they were shipped, brushed off, and stacked up ready for painting. Small benches were erected, and the accessories of the work, such as cans, brushes, pots, balances, etc., were placed in position.
=Methods Followed in Painting Plates.= A frame resting upon the workbench served to hold the plates in a lateral position while being painted, room being allowed beneath the plate for the operator to place his hands in order to lift the plates from the under surface after the painting had been finished.
A pickled plate having been placed upon the framework everything was in readiness for the work. The specific gravity and weight per gallon of the paint to be applied was determined, and the amount, in grams, to be applied to each individual panel was calculated according to the following formula:
Spreading rate Sq. ft. in plate Grams paint in gal. 900 sq. ft. : 6 :: 5400 : x
The reciprocal of _x_ being the number of grams of paint to be applied to the panels.
An enamel cup was then filled with the paint and a brush well stirred within. The cup, paint, and brush were placed upon the balances and accurately weighed in grams. After most of the paint had been applied to the panel, cross-brushing of the panel was continued until the pot with brush and paint exactly counterbalanced the deducted weight. The painted panel was then set in a rack, in a horizontal position to dry.
A period of eight days elapsed between the drying of each coat. The greatest care was taken in the painting of the edges of the plates, and the racks for containing the plates after they were painted were so constructed that the paint would not be abraded while sliding the plates back and forth. The working properties of each paint, and the appearance of the surface of each plate after painting, were carefully noted and included in the report. No reductions were made to any of the paints applied except in three cases, where the viscosity was so great that it was necessary to add a small amount of pure spirits of turpentine. The amount of paint was proportionately increased in such cases, so that the evaporation of the turpentine would leave upon the plate the amount of paint originally intended.
The appearance of the completed series of test panels is shown on page 221.
=Vehicles Used and Reasons for Avoidance of Japan Driers.= The pigments used were selected with the view to securing as nearly as possible purity and strength, and as already noted, were out of the same lots used in making the preliminary laboratory tests on inhibitives. They were ground in a vehicle composed of two parts of raw linseed oil and one part of pure boiled oil. Paint is generally caused to dry rapidly by the use of japan or driers. These materials contain a large amount of metallic oxides which might have some effect in either exciting or retarding corrosion. To prevent the introduction of such a factor, these materials were not used in the test. The boiled oil, with its small percentages of metallic oxides, was sufficient, however, to cause the paints to dry in a short time after they were spread.
=Testing Effect of Various Prime Coats.= Some of the special tests made included a series of plates prime-coated with different inhibitive pigments, and these tests were designed to determine which pigments offer the best results for such work. These plates were all second-coated with the same paint. It is the opinion of the authors that any good excluding paint may be used whether it be inhibitive in action or not, provided the contact coat is inhibitive. If, however, both coats can be designed so as to have the maximum possible value from both these points of view, the best results would, of course, accrue. The only way such data can be obtained is by careful observation of the results of exposure tests.
=Combination Formulas Tested.= By selecting a series of pigments which in the water tests showed inhibitive tendencies, and properly combining these pigments into a paint, it was thought possible that a more or less inhibitive paint would be produced. If this proved to be the case, it would follow that the selection and introduction into a paint of the stimulative pigments would inevitably produce a paint unfit for use on iron or steel.
=Data on Application of Paints.= The recorded data on the application of the paint to the panels is voluminous. There is presented herewith, however, the data on two of the paints.
NO. 2, QUICK PROCESS WHITE LEAD:
Sp. Gr. of pigment 6.78 Lbs. to gallon oil 20.34 Sp. Gr. of paint as received 2.47 Wt. of paint per gallon 20.56 Grams to panel 62 Condition of paint Good Working properties Works easy Drying 24 hrs. all coats
1 coat Oct. 26 T 60 B 29.94 W. fair 2 coat Nov. 3 T 54 B 30.23 W. clear 3 coat Nov. 7 T 52 B 29.66 W. cloudy
NO. 9, ORANGE MINERAL (AMERICAN):
Sp. Gr. of pigment 8.97 Lbs. to gallon oil 26.91 Sp. Gr. of paint as received 2.97 Wt. of paint per gallon 24.74 Grams to panel 74.7 Condition of paint Good Working properties Smooth--no brush marks Drying Good
1 coat Oct. 28 T 58 B 30.01 W. cloudy 2 coat Nov. 4 T 65 B 29.61 W. cloudy 3 coat Nov. 9 T 58 B 29.91 W. clear
=Composition of Paints.= The following table gives data regarding the composition, etc., of paints applied to the steel panels.
=Results of Inspection.= The results of an inspection of the steel test plates, made by Sub-committee D representing Committee D-1 of the American Society for Testing Materials, is herewith presented:
"On Wednesday, June 28, 1911, the second inspection of the Atlantic City Steel Test Panels, erected in October, 1908, was made by Sub-committee D of Committee D-1, this Committee having agreed to report upon the condition of the painted surfaces, leaving any report on the comparative corrosion of the various types of metal used in the test to Committee A-5 on the corrosion of iron.
===+=========================+=======+=======+======+=======+========= | | | | | |Grams | | | | | |Paint | | |Wt. of | Sp. |Wt. of |to Panel | Name | Sp. |Pigment| Gr. | Paint |at 900 | | Gr. |to Gal.| of | per |Sq. ft. Pigment |of Pig-|of oil |Paint | Gal. |spreading No.| | ment | Lbs. |Rec'd | Lbs. |rate ---+-------------------------+-------+-------+------+-------+--------- 1|Dutch process white lead | 6.83 | 20.49 | 2.45 | 20.49 | 61.0 2|Quick process white lead | 6.78 | 20.34 | 2.47 | 20.34 | 62.0 3|Zinc oxide | 5.56 | 16.68 | 2.12 | 16.68 | 59.0 4|Sublimed white lead | 6.45 | 19.17 | 2.36 | 19.17 | 59.0 5|Sublimed blue lead | 6.39 | 19.17 | 2.42 | 19.17 | 61.0 6|Lithopone | 4.26 | 12.78 | 1.80 | 12.78 | 45.3 7|Zinc lead white | 4.42 | 13.26 | 1.96 | 13.26 | 49.4 9|American orange mineral | 8.97 | 26.91 | 2.97 | 26.91 | 74.7 10|Red lead | 8.70 | 26.10 | 2.93 | 26.10 | 73.6 12|Bright red oxide | 5.26 | 15.78 | 2.05 | 15.78 | 60.0 14|Venetian red | 3.1 | 9.30 | 1.52 | 9.30 | 38.0 15|Prince's metallic brown | 3.17 | 9.51 | 1.50 | 9.51 | 37.7 16|Natural graphite | 2.60 | 7.80 | 1.37 | 7.80 | 34.4 17|Acheson graphite | 2.21 | 6.63 | 1.22 | 6.63 | 30.8 19| {Lampblack | | 1.82}| | 1.82 | | {Barytes | 1.82 | 8.92}| 1.60 | 8.92 | 40.2 20|Willow charcoal | 1.49 | 4.47 | 1.08 | 4.47 | 27.0 21| {Gas carbon black | 1.85 | 1.39}| 1.67 | 1.39 | | {Natural barytes | | 10.03}| | 10.03 | 50.7 24|French yellow ochre | 2.94 | 8.82 | 1.46 | 8.82 | 37.0 27|Natural barytes | 4.46 | 13.38 | 1.83 | 13.38 | 46.0 28|Precipitated barytes | 4.23 | 12.69 | 1.84 | 12.69 | 46.0 |(blanc fixe) | | | | | 29|Calcium carbonate | 5.48 | 8.22 | 1.37 | 8.22 | 34.5 |(whiting) | | | | | 30|Calcium carbonate | 2.56 | 7.68 | 1.35 | 7.68 | 34.0 |precipitated | | | | | 31|Calcium sulphate (gypsum)| 2.33 | 6.99 | 1.25 | 6.99 | 31.4 32|China clay (kaolin) | 2.67 | 8.01 | 1.34 | 8.01 | 34.0 33|Asbestine (silicate of | 2.75 | 8.25 | 1.38 | 8.25 | 34.7 |magnesium) | | | | | 34|American vermilion | 6.83 | 20.49 | | 20.49 | 64.5 |(chrome scarlet) | | | | | 36|Medium chrome yellow | 5.88 | 17.64 | | 17.64 | 67.1 39|Zinc chromate | 3.57 | 10.71 | 1.57 | 10.71 | 39.2 40|Zinc and barium chromate | 3.45 | 10.35 | 1.58 | 10.35 | 40.0 41|Chrome green (blue tone) | 4.44 | 13.32 | 1.94 | 13.32 | 49.0 44|Prussian blue | 1.96 | 5.88 | | 5.88 | 30.0 45|Prussian blue | 1.93 | 5.79 | | 5.79 | 34.5 48|Ultramarine blue | 2.40 | 7.20 | 1.29 | 7.20 | 32.5 49|Zinc and lead chromate | 4.76 | 14.28 | 1.92 | 14.28 | 48.3 51|Magnetic black oxide | | 15.00 | 1.92 | 15 | 48.3 | | | | | | | _Composite Paints_ | | | | | | | | | | | 111|Brown } Made from pig- | | 10.82 | 1.30 | 10.82 | 32.7 222|Black } ments that were | | 10.86 | 1.30 | 10.86 | 32.8 333|White } inhibitive in the| | 14.52 | 1.74 | 14.52 | 43.8 444|Green } water test | | 12.77 | 1.53 | 12.77 | 38.6 | | | | | | 555|Black } Made from pig- | | 9.37 | 1.125| 9.37 | 28. 666|Brown } ments that were | | 11.74 | 1.41 | 11.74 | 35.5 777|White } stimulative in | | 14.55 | 1.75 | 14.55 | 44. 888|Green } the water test | | 14.57 | 1.75 | 14.57 | 14.57 ===+=========================+=======+=======+======+=======+=========
"According to the amount of rust apparent on the painted surfaces of the panels, as well as the degree of checking, chalking, scaling, cracking, peeling, loss of color, and other signs of paint failure shown, ratings were given each panel. The system of rating which took into consideration all the above conditions, was similar to the system used at the first inspection during 1910, when 0 (zero) recorded the worst results and 10 (ten) the best results.
"In Table No. 1 there is shown the rating accorded by each inspector to each panel, as well as an average for each panel.
TABLE NO. 1.--SECOND INSPECTION OF STEEL PAINT TEST PANELS AT ATLANTIC CITY, N. J., BY SUB-COMMITTEE D OF COMMITTEE D-1
=======+========================+======+======+=======+=======+======= | | | | H. A. | | Panel | |W. H. |P. H. |Gardner| C. | No. | Pigment |Walker|Walker|Chair- |Chapman|Average | | | | man | | -------+------------------------+------+------+-------+-------+------- 1 |Dutch process white lead| 2 | 3 | 3 | 5 | 3.7 2 |Quick process white lead| 4 | 4 | 3 | 6 | 4.2 3 |Zinc oxide (XX) | 1 | 1-1/2| 1 | 2-1/2| 1.5 4 |Sublimed white lead | 9 | 9-1/2| 9 | 8-1/2| 9.0 5 |Sublimed blue lead | 9 | 9-1/2| 9-1/2| 7-1/2| 8.8 6 |Lithopone | 2 | 1-1/2| 2 | 3-1/2| 2.2 7 |Zinc lead white | 3 | 4 | 5 | 7 | 4.7 9 |Orange mineral | 9 | 9 | 9 | 6-1/2| 8.3 10 |Red lead | 9 | 9 | 9 | 6-1/2| 8.3 12 |Bright red oxide | 8-1/2| 9 | 8 | 7 | 8.1 14 |Venetian red | 7 | 9 | 7 | 9 | 8.0 15 |Prince's metallic brown | 5 | 7-1/2| 6 | 8 | 6.3 16 |Natural graphite | 6 | 8 | 4 | 9-1/2| 6.8 17 |Artificial graphite | 5 | 7-1/2| 4 | 7 | 5.9 19 |Lampblack | 5 | 7-1/2| 5 | 8 | 6.3 20 |Willow charcoal | 9 | 8-1/2| 9 | 9 | 8.8 21 |Carbon black | 7 | 8-1/2| 5 | 8-1/2| 7.2 24 |Yellow ochre (French) | 5 | 7 | 2 | 8 | 5.5 27 |Barytes (natural) | 1 | 1 | 1 | 0 | 0.7 28 |Barytes (precipitated) | 2 | 1-1/2| 2 | 2 | 1.8 29 |Calcium carbonate | 0 | 0 | 0 | 0 | 0.0 |(whiting) | | | | | 30 |Calcium carbonate (pre- | 0 | 0 | 0 | 0 | 0.0 |cipitated) | | | | | 31 |Calcium sulphate | 1 | 1 | 1 | 3 | 1.7 |(gypsum) | | | | | 32 |China clay (kaolin) | 6 | 6 | 7 | 6-1/2| 6.3 33 |Asbestine (magnes. sili-| 5 | 4-1/2| 6 | 5 | 5.1 |cate) | | | | | 34 |American vermilion |10 |10 | 10 | 10 | 10.0 36 |Lead chromate | 7 | 7-1/2| 8-1/2| 8 | 7.7 39 |Zinc chromate | 9 | 9 | 10 | 9-1/2| 9.5 40 |Zinc and barium chromate| 9 | 9-1/2| 10 | 9-1/2| 9.5 41 |Chrome green (blue tone)|10 |10 | 10 | 9-1/2| 9.8 44 |Prussian blue, W. S | 9 | 9-1/2| 9-1/2| 9 | 9.0 45 |Prussian blue, W. I | 8 | 9-1/2| 8-1/2| 8-1/2| 8.5 48 |Ultramarine blue | 0 | 0 | 0 | 0 | 0.0 49 |Zinc and lead chromate |10 | 9-1/2| 10 | 9-1/2| 9.7 51 |Magnetic black oxide | 9 | 9-1/2| 10 | 9-1/2| 9.5 111 |Brown composite paint | 7 | 9 | 9 | 9 | 8.5 222 |Black composite paint | 9 | 9 | 9 | 8-1/2| 8.8 3333 |White composite paint | 4 | 4 | 7 | 3 | 4.5 444 |Green composite paint | 5 | 7 | 7 | 8 | 6.7 555 |Black composite paint | 9 | 9 | 6 | 9 | 8.2 666 |Brown composite paint | 8 | 8 | 6 | 9 | 7.7 777 |White composite paint | 7 |10 | 5 | 7 | 7.2 888 |Green composite paint | 7 | 8 | 8 | 9 | 8.0 2000 |1 coat zinc chromate }| 8 | 8-1/2| 8 | 8 | 8.1 |1 coat iron oxide ex- }| | | | | |cluder }| | | | | 3000 |1 coat lead chromate | 7 | 8 | 7 | 7-1/2| 7.3 4000 |1 coat red lead }| 7 | 8-1/2| 8 | 7-1/2| 7.7 |1 coat iron oxide ex- }| | | | | |cluder }| | | | | 100 |Straight carbon black | 5 | 8-1/2| 4 | 8-1/2| 6.5 |paint with turps and | | | | | |drier | | | | | 90 |Straight lampblack paint| 5 | 7 | 3 | 8 | 5.7 |with turps and drier | | | | | 5555 |Coal tar paint over red | 4 | 8 | 2 | 7 | 5.2 |lead | | | | | 1000 |Chrome resinate in oil | 1 | 0 | 0 | 2 | 0.7 |(1 coat) | | | | | 1 plate|3 coats boiled linseed | 1 | 0 | 1 | 4 | 1.5 |oil | | | | | =======+========================+======+======+=======+=======+=======
"In Table No. 2 there is shown the rating obtained by those panels which were considered by the committee as meriting from 8 to 10, and having given the best all-round service.
TABLE NO. 2.--ANALYSIS OF AVERAGES. GRADE OF EXCELLENCE FROM 8 TO 10
=====+=============================================+======= Plate| Pigment |Average -----+---------------------------------------------+------- 34 | American vermilion (basic chromate of lead) | 10.0 41 | Chrome green | 9.8 49 | Lead and zinc chromate | 9.7 39 | Zinc chromate | 9.5 40 | Zinc and barium chromate | 9.5 51 | Black oxide of iron | 9.5 4 | Sublimed white lead | 9.0 44 | Prussian blue | 9.0 5 | Sublimed blue lead | 8.8 20 | Willow charcoal | 8.8 222 | Composite paint | 8.8 45 | Prussian blue | 8.5 111 | Composite formula | 8.5 9 | Orange mineral | 8.3 10 | Red lead | 8.3 555 | Composite paint | 8.2 12 | Bright red oxide of iron | 8.1 2000 | 1 coat zinc chromate; 1 coat iron oxide | 8.1 14 | Venetian red | 8.0 888 | Composite paint | 8.0 =====+=============================================+=======
=Comparison of Results.= It is of interest to compare with Table 2 of the above report, Table 2 of the 1910 report of Committee U of the American Society for Testing Materials. Both charts show the highly inhibitive pigments to be in the lead.
COMMITTEE U REPORT 1910
TABLE II.--ANALYSIS OF AVERAGES. GRADE OF EXCELLENCE FROM 8 TO 10
(_Only resistance to corrosion was considered, and only pigments which were common to both tests are included_)
===+====================================+======= No.| Pigment |Average ---+------------------------------------+------- 34 | American vermilion (chrome scarlet)| 9.8 41 | Chrome green (blue tone) | 9.7 40 | Zinc and barium chromate | 9.7 5 | Sublimed blue lead | 9.6 4 | Sublimed white lead | 9.5 49 | Zinc and lead chromate | 9.5 39 | Zinc chromate | 9.4 12 | Bright red oxide | 9.3 44 | Prussian blue (water stimulative) | 9.2 16 | Natural graphite | 9.1 9 | Orange mineral (American) | 9.0 36 | Medium chrome yellow | 9.0 2 | White lead (quick process) | 8.9 20 | Willow charcoal | 8.8 45 | Prussian blue (water inhibitive) | 8.8 1 | White lead (Dutch process) | 8.7 10 | Red lead | 8.7 7 | Zinc lead white | 8.0 ===+====================================+=======
The writer has recently made a careful inspection of the panels painted with single pigment paints, and has made the following brief summary of the characteristic appearance of each.
=Panel No. 1--Dutch Process White Lead.= The excessive chalking which took place began to disappear at the end of a year, being washed away by the rains and carried away by the winds, so that there was left upon the surface but a thin coating of pigment, insufficient to give good protection. Slight corrosion was apparent beneath the film.
=Panel No. 2--Quick Process White Lead.= In the same condition as Panel No. 1.
=Panel No. 3--Zinc Oxide.= Panel covered with thin lateral streaks of rust, due to the admittance of moisture in cracks caused by brittleness of film. Result doubtless due to insufficient amount of oil used with pigment. Removal of film shows steel very bright except where cracks have formed.
=Panel No. 4--Sublimed White Lead.= Although sublimed white lead chalked very heavily, the chalked pigment seemed to be tenacious and adhered to the plate, presenting an excellent surface with absence of rust. Film of good color and quite elastic.
=Panel No. 5--Sublimed Blue Lead.= In same condition as Panel No. 4, but color has slightly faded.
=Panel No. 6--Lithopones.= Lithopone was early destroyed, as is usual with this pigment when used alone on exterior surfaces. It became rough and discolored, presenting a very blotchy appearance and disclosed the formation of rust working through the film.
=Panel No. 7--Zinc Lead White.= In general good condition with the exception of the color, which is slightly dark. Medium chalking was apparent but only very slight corrosion appeared.
=Panel No. 9--Orange Mineral.= In excellent condition, showing a good firm surface with no checking or corrosion apparent. Shortly after exposure the film became covered with a white coating of carbonate of lead, which indicates action of the red lead with the carbonic acid of the atmosphere. Removal of this white coating with water discloses the brilliant color of the unaffected portion of the red lead.
=Panel No. 10--Red Lead.= In same condition as Panel No. 9.
=Panel No. 12--Bright Red Iron Oxide.= In general good condition. Film intact and unfading in color.
=Panel No. 14--Venetian Red.= Similar to Panel No. 12, but slight corrosion apparent beneath, in localized spots, and film showing slight wart-like formations.
=Panel No. 15--Prince's Metallic Brown.= Similar to Panel No. 14.
=Panel No. 16--Natural Graphite.= Deeply pitted in spots, showing bulbous eruptions, indicating the stimulative nature of this pigment.
=Panel No. 17--Artificial Graphite.= In same condition as Panel No. 16.
=Panel No. 19--Lampblack and Barytes.= Although the film seems to be intact, there are apparent abrasions of the surface showing stimulative corrosion effects of a pronounced nature.
=Panel No. 21--Carbon Black and Barytes.= In same condition as Panel No. 19.
The longevity of lampblack and carbon black paint films when applied to wood has been attributed to the slow drying nature of these pigments when mixed with oil. It is assumed that they have the property of keeping the oil in a semi-drying condition, which will not disintegrate as early as when the oil is thoroughly dried to linoxyn. If this is true, it would seem advisable to use with hard-drying pigments, a proportion of some oil that is semi-drying in nature or one which will leave a film not too hard. Soya bean oil, wood oil, and fish oil present themselves as candidates for such use. How they will work in practice, however, is a question not yet determined. On the other hand, it is well known that these pigments require enormous quantities of oil in order to grind to a working consistency, and it is possible that the life of such coatings is due rather to the property of these pigments, of taking up large quantities of oil, than to their effect upon the slow drying of oil. Excessive oil carrying, however, should be avoided, as shown by the early failure and pitting of those carbon black and lampblack paints ground with very large quantities of oil, as is the usual practice. When these carbon and lampblack pigments were ground with barytes (which is a heavy pigment and requires only about 9 pounds of oil to 100 pounds of pigment, as against 175 pounds of oil to 100 pounds of lampblack), it was found that the lampblack and carbon black paints were reinforced and made more suitable for actual practice. The stimulative nature of these black pigments, however, asserted itself in both cases, and large pittings and eruptions were evident at the end of a year. Carbon black, lampblack, graphite, or any other good conductor of electricity should never be placed next to the surface of iron. They are good as top-coatings, but not as prime-coaters. Some pigments are stimulators of corrosion, because they contain water-soluble impurities that hasten the rusting, while others, like graphite, hasten it simply because, being good conductors, they stimulate surface electrolysis.
=Panel No. 20--Willow Charcoal.= In excellent condition throughout. Presence of small quantities of potash may be responsible for the inhibitive nature of this black pigment.
=Panel No. 24--Ochre.= While the film seems intact, it has a very mottled appearance and examination shows eruptions of rust through the film, in several places.
=Panel No. 27--Natural Barytes.= Within a year the film became pin-holed, and corrosion was apparent. At the end of three years very little of the pigment was left upon the plate, having chalked and scaled off. Barytes has proved its usefulness as a constituent of a combination type of paint, but it should not be used alone.
=Panel No. 28--Blanc Fixe.= In the same condition as Panel No. 27, but slightly more chalking and disintegration was shown.
=Panel No. 29--Whiting.= Plates coated with calcium carbonate or whiting in oil presented a very fair appearance at the start of the test, but they soon began to chalk and disintegrate. It is well known that whiting, being alkaline, has the property of acting on oil and causing its early disintegration by saponification. As a matter of fact, six months after the whiting plates were exposed, crumbling of the surface appeared, and twelve months was sufficient for the total destruction of the paint. At this time the rusted surface of the plates which had been painted with calcium carbonate, seemed not to rust as fast as those plates which were exposed without paint coatings, and the rust which had formed appeared to be of an even, fine texture. On the lower left-hand corner of these plates had been lettered the figures "29" and "30," using lampblack in oil. One of the most remarkable things which appears on the fence to-day is the perfect condition of these lampblack letters over their priming coat of calcium carbonate, standing out in clear relief against the rusted metal. This test would suggest, therefore, that if the surface of metal is properly protected with a pigment which is slightly alkaline or inhibitive in nature, and then topped with a good weather-resisting material, such as lampblack, graphite or carbon black, good results would be obtained. Further tests will be made to determine the value of this suggestion.
=Panel No. 30--Precipitated Calcium Carbonate.= Showed more rapid destruction than Panel No. 29.
=Panel No. 31--Calcium Sulphate.= Under the paint film of gypsum, rust soon appeared, showing that the film was not a good excluder of moisture. Although the film remained intact, rusting progressed throughout the test and considerably darkened the color of the paint.
=Panel No. 32--China Clay.= This pigment gave excellent service for eighteen months. Afterwards indications of corrosion were shown, and apparent breakdown of the film was indicated.
=Panel No. 33--Asbestine.= In the same condition as Panel No. 32.
=Panel No. 34--American Vermilion.= This pigment has given perfect protection to the plates. The film is strong and elastic, and upon removal reveals the bright steel. No chalking, checking, discoloration, or other signs of paint failure are shown. It would appear that the inhibitive characteristics of this pigment are pronounced, and it promises to give efficient service for several years more.
=Panel No. 36--Lead Chromate.= This panel is in generally fair condition, but slight checking is shown.
=Panel No. 39--Zinc Chromate.= This panel is in condition similar to Panel No. 34, presenting a perfect appearance, with decided maintenance of color, elasticity of film, and freedom from any bad characteristics. It has proved to be one of the highest type rust inhibitive pigments.
=Panel No. 40--Zinc-and-Barium-Chromate.= Although the color of this pigment is not very pleasing, it has proved itself to be the equal of zinc chromate in its protective value.
=Panel No. 41--Chrome Green.= In excellent condition. Presents an appearance similar to Panels Nos. 34 and 39. Its surface is perfect and will doubtless give service for many years.
=Panel No. 44--Prussian Blue.= This panel stands forth as the most wonderful moisture-excluder in the whole test, its surface presenting an appearance similar to a varnished plate, even after three years' exposure. Action between the pigment and the oil, resulting in the formation of iron linoleate, may account for this property.
=Panel No. 45--Prussian Blue.= In same condition as Panel No. 44.
=Panel No. 48--Ultramarine Blue.= Soon after this test was exposed, early vehicle decay and excessive chalking were observed. The admittance of moisture may have caused the formation of acid with the sulphur content of the pigment, which would account for the rapid corrosion which followed. It is of a pronounced stimulative type. The effect of stimulative under-coatings is well shown on some special plates on the fence, which when received were not pickled before painting, but had upon their surfaces the ordinary coating of mill scale. Over this had been stencilled in a triangular form the trade mark of the manufacturer. The stencilling material was made of ultramarine blue. When these plates were painted with some of the special paints, and exposed, the stimulative nature of the ultramarine blue began to assert itself, and within a short time, wherever the stencil marks were located, signs of rust began to appear through the coatings of top paint which had been applied. Corrosion under these stencil marks became so great that the trade mark was plainly outlined in letters of rust. This would seem to be final proof that pigments of a stimulative nature should never be used for the priming of iron and steel.
=Panel No. 49--Zinc-Lead Chromate.= In excellent condition throughout, with a smooth surface and showing no corrosion. Stands in the same class as Panels Nos. 34 and 39.
=Panel No. 51--Black Magnetic Oxide of Iron.= In excellent condition.