Aviation Color Primers
Introduction to Aluminum Powders,
Alclad, Aluminum Primers and Paints
on US Military Aircraft 1924-1944
National Convention Special, Chicago, Illinois, July 2001
Aluminum, Earth’s most abundant metal, is rarely
found in a pure state. Highly reactive, with a voracious appetite for
oxygen, the element appears in nature as alumina, natural
aluminum oxide. By the early nineteenth century, British scientist Sir
Humphry Davy had joined the growing list of chemists trying to isolate
the metal. He failed, but he left the metal with a name. Well, three
names, actually. Davy’s first choice was alumium, a name he soon
switched to aluminum, the name now commonly accepted in the US.
This he subsequently changed to aluminium, as the metal is known
in Europe and the British Commonwealth.
Although aluminum was successfully isolated in
1825, by 1886 the world’s total production was still less than 100
pounds (45 kg). That year, experiments in the US and France
independently developed a new process that could produce nearly pure
aluminum at commercially acceptable prices. Aluminum was soon being
cast into engine blocks which weighed less than a third as much as
similar steel units. Although the surface of each aluminum block
rapidly formed a thin coating of aluminum oxide, the coating remained on
the surface. (Similar oxidation on steel would eventually rust through
the entire block.)
Pure aluminum was not strong enough to form
aluminum sheet; aluminum alloys could be successfully produced, but
proved susceptible to intergranular corrosion. The alloys required
priming, usually with the same oil-based primers used for steel and
iron. (The Air Corps’ 1938 list of approved primers showed the use of
commercial products named red oxide, plum, light grey, and pink.)
The Aluminum Company of America (Alcoa) developed a
new type of aluminum alloy sheet in the late 1920s. Named Alclad,
the sheet was rolled with a thin layer of pure aluminum, protecting the
internal alloy from corrosion.
By the early 1930s, a zinc chromate primer had been
developed, apparently by the Ford Motor Company. The primer proved
popular in commercial aviation, but was foolishly rejected by the
military for nearly four years.
Primers and Paints
The following notes follow the early development of
the Army’s (and, to a lesser degree, the Navy’s) interest in powdered
aluminum, Alclad, and various primers and paints.
20 Jun 1924 Army spec 3-44A for Bronze Powder,
Aluminum allows maximum of .15% copper and .05% lead.
20 Jul 1926 Army spec 3-100 lists protective
coatings for steel as zinc plating, cadmium plating,
“Parkerizing, [phosphate treatment]” Indian Red (Fe2O3)
oil-based primer, or 1 lb polished aluminum powder in 1 gal spar
varnish followed by 2 coats air drying enamel. Protective coatings for
aluminum to be Indian Red primer followed by 2 final coats of
aluminized spar varnish. Exterior of cowling can be not less than 2
coats spar varnish or colored enamel.
06 Oct 1930 Ford memo notes that the Air Corps
rejected zinc chromate primer.
15 Dec 1930 Army spec 3-100B makes first mention
21 Apr 1931 Report lists finishes for
aluminum & alloys: 1 coat oil base metal primer & 2 coats of
pigmented nitrate dope or 3 coats of semi-pigmented dope or 1
coat of iron oxide chromate primer with two coats of oil enamel.
17 Nov 1931 Spec 3-100C notes that aluminum
cowling interiors need not be painted.
13 Oct 1934 Panagra memo notes use of
Ford zinc chromate for about 3 years and DuPont zinc chromate for about
03 Dec 1934 Panama Air Depot memo requests
zinc chromate primer; Air Corps has used it for at least 1 year with
28 Mar 1935 Berry Brothers zinc chromate
primer is approved; no specification is yet prepared, since material
settles out in the can.
25 Jul 1935 Memo lists 3 approved zinc
chromate primers; Ford primer is now made by Sherwin-Williams.
09 Oct 1935 Spec 3-100F notes no additional
paint coating required on exterior surfaces of Alclad skins.
01 Sep 1936 Materiel Division memo desires
standardization of cockpit colors. A-17 has light green, C-33 has a
dark shade of green.
26 Sep 1936 Spec 3-100G makes first mention of
zinc chromate primer in specs! Oil base metal primer still
14 Nov 1936 Instructions for use of zinc chromate
primer notes adding 4-oz of aluminum powder to 1-gallon of primer
for second coat.
29 Mar 1937 Wright Field memo recommends 1 brush
coat of bronze green lacquer or enamel to eliminate glare
on noses of C-32, C-33, and C-34.
11 Aug 1938 Spec 3-100H notes interior finish
to be 1 coat of iron oxide primer or zinc chromate primer,
followed by one or more coats of the same primer containing aluminum
powder, OR 1 coat of either primer followed by one or more coats of
aluminum enamel or lacquer, OR one or more coats of aluminum bituminous
paint. Cockpit colors not mentioned.
16 Nov 1938 Materiel Division report to Navy
mentions that the Army has used zinc chromate primers exclusively
for the past several years.
09 Sep 1938 Spec 98-24113A for the first time
lists Yellow Green for cockpits which are open or under sliding
enclosures or Flat Bronze Green for closed cockpits, “the
top and sides of which form part of the fuselage structure” (sides above
windows and ceilings to be aluminum.)
15 Aug 1939 Overhaul instructions for B-18:
aluminized spar varnish over 1 coat zinc chromate primer; Pilots’ and
Radio Operator’s compartments finished with Pine Green Duco
246-30966; exterior anti glare panels (starting with aircraft 36-343)
Bronze Green; interior details and fittings Light Gray Duco
258-38141 and Dark Gray Duco 258-38142.
19 Jan 1940 Navy Spec SR-15C identifies “cockpit
green” color as “dull bronze green lacquer, Army color #9.”
28 Nov 1940 Navy memo notes that Spec L-12a
“...has been revised to replace the current Dull Bronze Green...with [Dark
Green #30] lacquer...”
17 Dec 1940 Army memo accepts Dull Dark Green
for cockpits and anti-glare.
01 Feb 1941 Army memo cancels list of
approved oil base metal primers; they are replaced by zinc
03 Feb 1942 To conserve aluminum pigment,
Navy memo recommends tinting second coat of zinc chromate primer with
Indian Red, lampblack, or other suitable indicator. Light gray can be
used on fabric surfaces where aluminum dope has been used.
31 Aug 1942 Curtiss-Wright memo reports Berry
Brother 174-G-13 to be used as “Curtiss Cockpit Green.”
10 Sep 1942 Navy memo proposes to replace dull
dark green with new green standard for cockpits. Proposed color can be
procured as lacquer, or made from zinc chromate primer, tinted with
11 Sep 1942 Army Spec 3-100H drops aluminum from
formula for yellow green finish.
21 May 1943 Wright Field memo notes: “The color
for Interior Green 611 is considered more yellow than the
pigmented zinc chromate currently used in Army aircraft...”
17 Nov 1943 Army Spec 98-24113B calls for flat
black on interior parts which reflect in canopies, turrets, etc
and medium green for interior portions of cockpits which are
visible to crew members in flight, and are subject to direct rays of the
sun. Seats and drapes are still Dull Dark Green.
19 Feb 1944 Wright Field notes that B-17,
B-25, P-51, and AT-6 have been manufactured without protective
coatings on internal surfaces for approximately 2 years.
Deviations granted to increase production.
29 Jul 1944 Wright Field notes that B-29
interspar upper wing panels are not built with Alclad; panels are
anodized with 1 coat of zinc chromate primer, then sprayed with two
coats of aluminized lacquer
Formulas for Aluminizing
The Army used a number of formulas for
“aluminizing” various coatings. What follows is a partial list of those
1 gallon spar varnish
- 1 pound polished aluminum powder
1 gallon spar varnish - 1.5 pounds
1 gallon spar varnish - 1.5 pounds
1 gallon clear varnish - 12 oz aluminum
1 gallon of clear dope
- 4 to 6 ounces aluminum powder
1 gallon of clear dope - 8 ounces
1 gallon of clear dope - 1 pound
1 gallon oil base primer
- 1 pound aluminum powder
1 gallon oil base primer - 1.5 pounds
1 gallon bitumostic paint
- 1 pound aluminum powder
1 gallon bituminous paint - 1.5 pounds
1 gallon bituminous paint - 2 pounds
1 gallon clear lacquer
- 8 to 12 oz extra-fine aluminum powder
1 gallon clear lacquer - 10 oz aluminum
1 gallon clear lacquer - 1 lb aluminum
1 gallon clear lacquer - 12 oz aluminum
1 gallon clear lacquer - 1 pound
Formulas for Tinting Zic
A similar variety existed in formulas for tinting
Zinc Chromate. Navy, Air Corps and AAF records show the following
additions to 1 gallon of zinc chromate primer:
aluminum powder: 4 oz
aluminum powder: 6 oz (or aluminum paste: 8 oz)
aluminum powder: 4 oz; black enamel: 1 pint
(1/8th gallon); toluene: 1 gallon
aluminum powder: 4 oz; black enamel: 1/10th gallon
aluminum powder: 4 oz; black enamel: 1/10th gallon; toluene: 1 gallon
aluminum powder: 6 oz (or aluminum paste 8 oz); black enamel: 1/10
gallon; toluene: 1 gallon
aluminum paste: 4 oz; black enamel: 1/10 gallon; toluene: 2 gallons
aluminum paste: 2 oz; thinner: 1½ gallons
Indian Red paste: 2 oz; thinner: 2 gallons
carbon black tinting paste: 2 oz
carbon black tinting paste: 8 oz
black tinting paste or black enamel: 1/10th gallon; toluene
substitute: 1 gallon
Text Copyright © 2002 by Dana Bell
Page Created 04 November, 2002
Last updated 04 November, 2002
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