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 resume, 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.
[Illustration: A Side View of Steel Test Fences]
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.
[Illustration: Three Photomicrographs of Corroding Steel]
=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.
[Illustration: Ferroxyl Tests on Painted Steel Surfaces. Upper Row
Painted with Stimulative Paints--Lower Row with Inhibitive Paints.]
[Illustration: Water Test on Plates Painted--Except in Center Spot. Left
Hand Plates Painted with Stimulative Paints, Right Hand Plates Painted
with Inhibitive Paints.]
[Illustration: View of Steel Plates Painted with Stimulative Paints,
after Immersion in Ferroxyl Jelly.]
"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.'"
[Illustration: Apparatus for Testing the Inhibitive Value of Pigments]
=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 resume 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.
[Illustration: Front View of Steel Test Fences]
=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.
[Illustration: Corrosion Pits on Graphite Panel]
[Illustration: Rust on Stripped Graphite Film]
[Illustration: Section of Wire Painted with a Stimulative Carbonaceous
Paint]
[Illustration: Corroded and Pitted Surface of Plate Painted with
Stimulative Paint]
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.
[Illustration: Panel Painted with Blanc Fixe. Right Side Stripped of
Paint to Show Corrosion]
[Illustration: Scaled Whiting Films
Chemically Active Pigments and Their Effect After Eighteen Months'
Wear]
[Illustration: Plate Showing Effect of Chemically Active Pigments on Oil
after One Year's Wear]
=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.
[Illustration: Corrosion Adhering to Film Stripped from Panel Painted
with Gypsum (Calcium Sulphate)]
=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.
[Illustration: China Clay
Asbestine
Gypsum]
=Panel No. 33--Asbestine.= In the same condition as Panel No. 32.
[Illustration: Excellent Surface shown by American Vermilion after
nearly Four Years' Exposure]
=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.
[Illustration: Perfect Condition of Plate Painted with Zinc Chromate;
One Half Stripped. (_Negative cracked_)]
=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.
[Illustration: Effect of Stimulative Paint. Manufacturer's Trade Mark
Stencilled on Bare Metal in Triangular Form, showing Through Subsequent
Paint Coating]
=Panel No. 51--Black Magnetic Oxide of Iron.= In excellent condition.