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APR 1 3 1970

BUILDING SCIENCE SERIES

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EPARTMENT

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National

Bureau

of Standards

1964 Exposure Test

of Porcelain Enamels

on Aluminum

Three Year Inspection

r \
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UNITED STATES DEPARTMENT OF COMMERCE • Maurice H. S tans. Secretary

NATIONAL BUREAU OF STANDARDS^* Lewis M. Branscomb, Director

1964 Exposure Test

of Porcelain Enamels on Aluminum

Three Year Inspection

Margaret A. Baker

Building Research Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Building Science Series 29 ^

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 29, 13 pages (April 1970) CODEN: BSSNB

Issued April 1970

For sale by the Superintendent of Documents, U.S. Governmenr Printing Office Washington, D.C. 20402 (Order by SD Catalog No. C 13.29/2:29), Price 25 cents.
NATIOi^AL BUREAU OF STANDARDS

APR 1 3 1970
Contents

p«g<> 1. Introduction 1

2. Materials and Procedures 1

2.1. Enamels 1

2.2. Test Specimens 1

2.3. Exposure Sites 1

2.4. Cleaning of Specimens 2

2.5. Acid Resistance 3

2.6. Thickness , 3

2.7. Gloss and Color 3

3. Results and Discussion 3

3.1. Visual Observation of Enamels 3

a. Amount of Soil Retained 3

b. Spalling 3

c. Visual Evaluation of Gloss and Color 3

3.2. Instrumental Determinations of Color and Gloss 3

3.3. Comparison of Exposure Sites 4

3.4. Effect of DiflFerent Colors 4

3.5. Effect of Initial Gloss 4

3.6. Effect of Coating Thickness 5

3.7. Correlation with Accelerated Tests 9

3.8. Correlation with Enamels in a Previous Exposure Test 10

3.9. Nature-Tone Enamels on Aluminum 10

4. Summary H

5. References H

1964 Exposure Test of Porcelain Enamels

on Aluminum—Three Year Inspection

Margaret A. Baker *

An exposure test of porcelain enamels on aluminum was initiated by the National Bureau of Standards and the Porcelain Enamel Institute in 1964 The enamels were returned from the exposure sites to the laboratory at NBS to be measured for changes in gloss and color after exposures of six months, one year, and three years. Changes were found to be greatest at Kure

Beach and least at Montreal and Los Angeles, with moderate changes occurring at Washington and New York. Although the boiling citric acid test is used as an acceptance test for these enamels, the

correlation with color change, particularly at Kure Beach, was not as good as expected. A cupric

chloride test was developed which shows an improvement in this correlation. Key words: Color; gloss; porcelain enamel on aluminum; weather resistance.

1 . Introduction

The application of porcelain enamels to aluminum

is a relatively recent development in the field of porcelain enameling. A few of the early porcelain enamels

on aluminum included in an exposure test initiated in 1956 [1] ^ indicated that accelerated tests used with

confidence for porcelain enamels on steel were not

reliable indicators of the weatherability of the new,

lower firing porcelain enamels on aluminum. Therefore the Aluminum Council of the Porcelain Enamel

Institute agreed to sponsor, with the National Bureau

of Standards, an exposure test consisting solely of porcelain enamels on aluminum. Nine colors used in

porcelain enamels on aluminum and enamels varying

in initial gloss and thickness were tested. The enamels in this test are exposed at Kure Beach,

North Carolina; New York, New York; Washington,

D.C.; Los Angeles, California; and Montreal, Canada.

They were inspected after exposures of six months, one year, and three years and were returned to the exposure racks for further exposure. This report is a summary of the results of these three inspections. The

next inspection is tentatively scheduled after five years

of exposure.

2, Materials and Procedures

2.1. Enamels

Sixteen enamel systems were included in this test, These enamel systems were represented by nine colors, three gloss ranges, and both one- and two-coat enamels

as indicated in table 1. The enamels in this test were coded for identification. Each enamel system can be identified by the

first two code letters. The first letter is always A. and

indicates an enamel on aluminum. This letter may

seem redundant but it is included because the manufacturers recognize their enamels by the three letter code. The second letter indicates the enamel system

color, number of coats, and gloss range—while the

third letter indicates the different fabricators for each

system. The differences between the enamel systems

are apparent (see table 1) for all systems except AA

and AZ, which were planned to have significantly

different thicknesses. However, this difference was not

attained during manufacture.

When variations in milling and firing of the enamels

by the different fabricators are taken into account,

there are, in effect, 51 different enamels included in

this test.

2.2. Test Specimens

Each enamel was sprayed onto a 3 X 5-ft sheet of

0.064-in 6061 aluminum alloy. After the enamel was

fired the sheet was cut with a band saw into a seventyeight 4yi6-in-square and nine 4 X 6-in exposure

specimens. This was done to obtain more uniform

specimens than could be obtained by spraying and

firing small individual metal blanks. Also, the speci- mens thus obtained would more closely simulate actual production enamels than small individually prepared

specimens.

2.3. Exposure Sites

Three of the 4'%6-i"-square specimens of each

enamel were exposed on the roofs of Federal Govern- ment Buildings in New York, N.Y. ; Los Angeles, Cali- fornia; and Washington, D.C, ; as well as on the roof

of the Stores Department Building in Montreal, Canada. Three of the 4 X 6-in specimens of each en;uiiel

* Research Associate from the Porcelain Enamel Institute at tl.e Nli:iol.il Bureau of Standards, 1964 to present.

' Figures in brackets indicate the literature references at the er. l of tl:is paper.

1
were exposed at a ground site of the International

Nickel Company's Corrosion Laboratory at Kure

Beach, North Carolina, 80 feet from the ocean. In

addition to the exposed specimens, three specimens of each enamel were stored for reference purposes. The

remaining specimens of each enamel were kept for use in laboratory tests and for the development of new

test methods.

2.4. Cleaning of Specimens

The enamel surface was cleaned before being measured for gloss and color. The cleaning treatment consisted of (1) scouring 30 strokes with a sponge that had been dampened with a 1 percent solution of trisodium phosphate and sprinkled with calcium car- bonate, (2) rinsing with tap water, (3) rinsing with

Table 1. Initial data for porcelain enamels on aluminum

Enamel

Specified properties Measured properties

Visual

color Nominalgloss Numberof coats Specular

gloss Thickness^

Boiling ^ acid

solubility

Acid d spot test ratings

mils AA—

A

White High Two 70.1 4.5 5.5 A

AA-B 74.2 4.3 5.9 AA-C 7l!5 3.4 5.0 AA

AA~D 71.9 6.5 12.7 AA

AB-A White Medium Two 56.8 4.0 7.2 B AB—

C

55.6 4.0 4.9 AB—

D

28.9 6.2 7.9 A

AC-A White High One 74.5 3.5 6.4 A

AC-B 71 .8 2.8 11.3 AA

Apr* 70.5 3!3 9^9 AA

AD-A White Medium One 55.0 2.8 6.2 AA

AD-B 68.3 4.3 6.7 B AD—

C

42 .4 3 .2 7 1 AD—

D

34.9 2.7 12 .4 A

AE-A Black High One 75.6 2.4 6.5 A

AE-B 78.0 1 .6 10 1 ACj—(_< 78.1 2^0 12.1 A

AE—

D

75.0 3.4 15.5 B AF-A Black Medium One 78 4 1 .5 14 2 AF—

B

58^5 2^7 9.0 B

AF—

C

76.8 3.1 10.1 C AG-B Black Low One 26 0 3 0 DD AG—

C

12.6 2^0 ^7^5 A AH-A Red High One 46.9 2.8 7.4 A

AH-B 85 3 3 1 8.8 B AH—

C

85^6 3!l 6.5 B AH—

D

82.0 1.9 10.5 B AO-A Dark green nign One 78 8 3 2 19 .9 A

AO—

B

79^8 1.6 10.1 A AO—

D

78.3 2.1 17.0 A

AP-A Light green 42 .4 6.4 12 3 g AP—

B

38^5 4^1 6^4 A

AP-C 30.2 4.0 6.2 A

AP-D 45.3 6.4 10.0 A AR-A Light green Low Two 9.6 3.2 4.4 A

AR-B 7.3 2.7 5.5 A

AR-C 5.7 4.3 8.1 A

AS-A Grey Medium Two 64.9 5.0 13.4 A

AS-B 61.6 5.5 7.4 AA

AS-C 62.2 3.9 5.4 A

AT-A Blue Medium Two 32.9 4.4 6.2 A

AT-B 54.8 3.6 7.0 A

AT-C 62.4 2.9 6.1 AA AU-A Brown Medium Two 50.0 7.2 5.3 A

AU-B 35.4 6.4 7.5 A

AU-C 46.6 4.4 7.6 A AW-A Yellow Medium Two 62.4 5.8 7.8 A AW-B 63.1 4.1 8.7 A AW-C 80.9 5.0 18.6 A AZ-A White High Two 72.0 4.2 9.5 A

AZ-B 71.2 2.7 5.2 A

• The 45° specular gloss was measured in accordance with ASTM designation C-346.

>> The thickness was measured in accordance with ASTM designation E-376.

" The boiling acid solubilities were determined in accordance with ASTM designation C-283.

<i The acid spot test ratings were determined in accordance with ASTM designation C-282. 2
distilled water, and (4) rinsing with alcohol. Before

adopting this cleaning procedure, representative speci- mens of low, medium, and high gloss enamels were

scoured with calcium carbonate for 650 strokes. No

change in gloss was noted on the high gloss enamels

while an increase of about 5 percent was noted after 350 strokes on both the medium and low gloss enamels.

The gloss increased by about 15 percent after 650

strokes. The increase caused by the scouring may be

the result of a smoother surface which reflects light better than the original surface. Since the increase was only 5 percent after 350 strokes (enough for 10

inspections) it was thought that this treatment would

not significantly affect the exposure test results. The

scouring treatment produced no noticeable color change.

2.5. Acid Resistance

The acid resistance of porcelain enamels on aluminum is measured by either the boiling acid

solubility test [2] or by the citric acid spot test [3].

The enamels are rated by the boiling acid solubility

test on the basis of weight loss per unit area; the enamels with the best acid resistance have the lowest weight loss. In the citric acid spot test the enamels

are divided into five categories: AA, A, B, C, or D,

with respectively decreasing acid resistance. Both

the boiling acid solubility and citric acid spot test ratings for the enamels included in this test are pre- sented in table 1.

2.6. Thickness

The enamel thickness was measured at four loca- tions on each specimen with an eddy current thick- ness gage [4] . The average thickness for each enamel

is presented in table 1.

2.7. Gloss and Color

The 45-degree specular gloss of the enamels was

measured [5] at four orientations near the center of the specimen before and after exposure. The average

initial gloss for each enamel is given in table 1. The

gloss after exposure is reported as the percentage gloss

retained. The color is measured before and after exposure

with a color difference meter [6]. One of the three average storage specimens of each enamel was selected

as the color standard to obtain the maximum efficiency

possible with this type of instrument. The color change was calculated [7] from the color values and is re- ported as color retention which is 100 minus the

color change in NBS units.

3. Results and Discussion

3.1. Visual Observation of Enamels

a. Amount of Soil Retained

A visual examination revealed that enamels exposed

at New York City had the most dirt adhering to them

while those exposed at Los Angeles, Washington,

Montreal, and Kure Beach had respectively cleaner

surfaces. The dirt deposits were readily removed from

the enamels exposed at all sites except New York by

the cleaning procedure outlined in section 2.4. The

enamels exposed at New York required vigorous

scouring with a sponge that was sprinkled with cal- cium carbonate to remove the dirt film.

b. Spalling

After the specimens were cleaned it was observed

that "fishscale" type spalling occurred on some enamels

exposed at all sites. In no case was the spalled area

large enough to constitute failure [8]

.

c. Visual Evaluation of Color and Gloss The enamels exposed at Washington, New York,

Montreal, and Los Angeles appeared to have good

color and gloss retention with the exception of the red enamels, which appeared lighter than the unex- posed enamels. Many of the enamels exposed at Kure

Beach had obviously undergone substantial color changes. The reds, blacks, dark greens, and blues

lightened considerably. The red, dark green, and blue enamel surfaces had the appearance of light particles

surrounded by a darker colored matrix, while the black

enamel surfaces appeared uniformly lightened. Many

of the white enamels exposed at Kure Beach appeared

to be yellowing. The weathering of some of the enamels exposed at Kure Beach had progressed to a point where changes in the gloss were readily apparent

and the surfaces appeared chalky.

3.2. Instrumental Determinations of Color and

Gloss

The average color- and percentage gloss-retention values obtained from the six-months', one-year's and

three-years' inspections of these enamels are presented

in tables 2 and 3. The data in figures 1 and 2 indi- cate that gloss does not change as uniformly with exposure time as color. The nonuniformity is probably caused by the exceptionally large percentage

changes which result from small gloss changes for the low gloss enamels. For example, a change of one

gloss unit will produce a 17 percent change in the

gloss retained for low gloss enamel, AR-C, but only

a 1 percent change for high gloss enamel, AO-A. The

increase in percentage gloss retained for many of the low gloss enamels after three years' exposure (see table 3) may be caused by a smoothing of the surface by the weather. An increase in the gloss-rentention values of many

low and medium gloss enamels exposed at New York

City was also observed. These increases are attributed more to the severe scouring treatment necessary to

3
Figure 1. The effect of exposure time at the five weathering sites on the color retention of porcelain enamel on aluminum.

clean these specimens than to the action of the weather.

Since the percentage gloss-retention values were more variable than the color-retention values, the remainder of this report will be based primarily on

color retention.

3.3. Comparison of Exposure Sites

The color-retention data were subjected to a twosided sign test [9] to determine if the exposure conditions at the various sites caused significant differ- ences in the color retention of the enamels. The

exposure sites were divided into three categories on

the basis of the observed results of the sign test. Kure

Beach was in a category by itself and caused the

greatest color change in the enamels. New York and

Washington were grouped together and caused less severe color changes than Kure Beach but more severe than the sites in the third category, Montreal and Los

Angeles.

3.4. Effect of Different Colors

The average color retentions for the nine enamel

colors are presented in table 4 and figure 3. It can

be seen that large color changes occurred for the red

enamels exposed at all sites. This was expected since

all the red enamels included in this test failed the

nitric acid test for color retention [10] and would not be recommended for outdoor exposures. Large color changes also occurred on the blaek,

dark green, grey, and blue enamels exposed at Kure

Beach. These changes were not predicted by any of

the current tests for porcelain enamels on aluminum.

3.5. Effect of Initial Gloss

The enamels included in this test program were pro- duced in three gloss ranges; low, having an initial 45-degree specular gloss of 35 or less; medium, be- tween 36 and 69; and high, 70 or over. The average

color-retention data (top section of table 5) indicate 4
Table 2. Percentage gloss-retained data for the enamels exposed for three years in the 1964 exposure test of porcelain enamel on aluminum

Average percentage of initial gloss retained for enamels exposed at;»

E amel Kure Beach New York Washington Los Angeles Montreal

6-Mo. 1-Yr. 3-Yr. 6-Mo. 1-Yr. 3-Yr. 6-Mo. 1-Yr. 3-Yr. 6.Mo. 1-Yr. 3-Yr. 6-Mo. 1-Yr. 3-Yr. AA-A 85.5 95 2 46 9 98 3 96.5 96.3 93 .2 91 .6 96 9 95 6 97.8 94 1 93.8 90.4 92.6 AA-B 94.0 87 5 98 9 94 5 93.5 90.8 92.7 91 .5 94 3 103 0 100.9 95 1 98.6 93.2 90.3 AA-C 90.7 107 4 94 6 92 3 89.6 90.6 90.7 90.8 102 1 96 0 96.8 90 9 92.0 87.6 90.8 AA-D 76.0 33 0 7 8 101 1 97.8 97.4 94.6 92.5 25 0 101 0 100.4 93 100.0 93 .

1

69.3 AB-A 81.2 88 4 42 6 95 9 94.2 102.5 82.8 80.9 75 3 84 5 88.3 84 8 83.9 95.7 81.5 AB-C 79.6 86 4 63 6 83 9 84.4 86.7 81 .0 33 .6 79 7 83 6 87.9 84 6 82.7 82.7 82.3 AB-D 75.3 80 2 25 8 100 5 112.1 118.6 93.3 92 .0 94 2 79 6 98.1 99 1 80.0 95.9 100.8 AC-A 90.2 90 7 80 0 96 3 93.1 85.3 93.0 91.8 94 8 102 6 101.0 95 5 98.6 93.1 91 .5 AC-B 85.8 37 3 8 2 103 4 98.4 95.9 92.8 90.2 49 7 102 1 101 .3 98 7 101.3 97.1 87.0 AC-C 90.6 65 3 14 1 99 0 96.8 99.4 93 .7 92 .

1

91 7 98 2 98.1 95 0 98.3 94.1 93.1 AD-A 87.6 96 9 43 4 100 9 99.9 101.9 91.7 91.1 94 9 90 3 95.7 94 6 90.3 91 .1 92.3 AD-B 89.0 93 8 94 1 97 4 94.5 95.0 89.8 88.9 87 0 92 4 94.9 92 4 90.5 88.2 88.8 AD-C 82.8 91 3 27 6 105 3 106.4 116.3 90.9 90.3 92 2 87 5 95.4 94 7 88.6 94.5 95.5 AD-D 87.5 58 0 19 7 104 7 114.6 118.6 98.0 96.5 41 1 88 6 103.1 104 8 87.7 100.3 91.6 AE-A 76.4 68 4 49 7 82 1 80 .3 80.8 81 .3 80.5 78 8 80 5 80.5 78 5 82.1 80.2 80.3 AE-B 65.1 55 8 16 7 84 6 83.7 82.7 86.5 82.9 78 9 87 9 86.6 81 9 88.8 95.1 80.7 AE-C 72.6 68 2 36 4 86 7 83.7 83.8 89.4 85.6 80 8 91 1 89.9 84 7 91 .9 85.1 83 .0 AE-D 71.1 37 8 8 2 83 3 79.9 80.2 82.2 78.4 76 3 85 5 83.2 78 9 87.4 83.0 78.3 AF-A 65.6 67 9 23 5 82 1 82.1 98.0 85.7 80.0 76 3 85 7 84.3 81 9 90.4 84.3 79.5 AF-B 69.7 58 5 16 2 88 3 95.3 81 .7 84.5 91.7 89 6 96 1 96.5 94 3 95.6 95.3 94.6 AF-C 72.2 76 8 42 0 84 4 83.3 79.7 84.5 82.6 77 2 87 5 86.6 81 4 88.2 85.4 81.2 AG-B 82.0 83 7 39 6 76 2 100.4 108.1 100.5 97.8 93 4 79 5 103.1 103 3 98.9 100.5 104.6 AG-C 46.9 112 8 78 4 35 9 101 .0 127.2 105.7 100.8 85 3 33 2 103.8 109 8 31 .8 97.0 107.5 AH-A 90.8 79 3 51 6 118 3 121.3 103.8 95.8 96.6 97 1 103 7 113.2 111 7 97.8 103.6 103.8 AH-B 64.3 44 8 8 5 81 7 75.6 76.8 72.3 70.0 65 4 76 8 77.6 73 3 75.4 75.7 71.5 AH-C 73.9 59 2 43 6 79 0 75.6 77.1 70.8 68.5 67 8 77 6 77.4 70 8 77.3 93.6 70.4 AH-D 59.7 37 8 6 5 79 0 77.0 77.6 74.7 70.6 64 5 83 2 81.8 75 2 82.8 77.6 66.5 AO-A 76.6 60 9 35 4 80 2 78.5 81 .6 82.1 79.3 78 4 83 3 83.3 79 0 83.8 81 .4 80.6 AO-B 72.5 67 0 34 3 83 0 83.1 80.4 84.0 82.7 76 4 84 6 86.0 81 3 83.4 83.1 80.0 AO-D 74.1 50 8 15 2 81 0 79.1 73.2 83.8 80.7 77 7 87 0 84.2 79 1 87.8 84.9 81.2 AP-A 82.2 80 4 16 3 102 3 104.9 113 .0 95.5 93 .4 84 1 90 2 97.4 95 2 92.1 98.3 95.0 AP-B 75.5 87 1 78 6 86 3 94.6 109.8 82.9 81 .9 80 0 77 0 89.6 86 2 78.6 82.8 85.5 AP-C 73.9 84 1 84 3 85 8 98.9 116.6 85.7 83.9 82 7 72 5 91 .3 88 2 85.7 83.9 90.0 AP-D 87.5 88 9 42 7 95 4 100.8 111.3 93.9 93.4 92 7 88 0 95.2 93 4 91.7 94.7 96.7 AR-A 47.0 128 2 109 4 54 2 138.4 174.5 111 .8 104.8 95 7 25 5 122.2 128 8 62.4 106.5 118.1 AR-B 0.0 96 1 60 7 0 0 110.9 157.0 82.5 74.7 59 7 0 0 81 .7 101 7 4.4 73.6 97.4 AR-C 0.0 i05 9 70 0 0 0 84.6 117.0 85.7 81.6 58 2 0 0 81.6 109 0 0.0 69.6 105.3 AS-A 78.2 59 5 22 2 91 7 88.3 93.9 90.2 93.0 75 4 92 1 93.0 88 6 91 .2 89.7 87.3 AS-B 83.7 86 4 33 6 85 0 84.5 92.6 83.0 82.3 81 3 82 5 84.6 82 8 83.0 82.3 81.9 AS-C 92.5 97 7 80 7 90 4 89.9 96.5 91.8 92.2 93 1 93 3 95.5 91 5 91.7 89.1 90.6 AT-A 75.2 93 8 82 2 80 4 94.1 116.0 83.8 83.2 72 9 71 4 91.0 87 3 68.3 83.1 87.4 AT-B 79.8 93 4 38 0 91 5 95.6 107.3 93.8 94.1 97 2 90 9 95.5 92 8 91.5 90.9 94.9 AT-C 81 .

5

82 0 32 4 83 3 83 0 89 5 78 8 79 2 76 2 82 0 84 0 80 8 80 9 79 9 77 5 AU-A 89.1 89 8 99 1 88 3 90.7 104.0 84.3 84.9 84 4 87 7 92.5 86 3 81.2 83.4 85.5 AU-B 75.7 93 4 70 1 98 0 108.1 121.5 92.4 91.8 86 4 80 3 94.9 94 6 79.9 89.7 94.2 AU-C 87.4 94 7 72 3 95 1 98.0 106.1 94.5 93.9 92 9 91 4 97.9 95 9 91.5 93.5 95.3 AW-A 81.4 80 1 98 0 86 2 85.1 87.8 82.7 81.5 77 9 85 3 85.8 83 2 85.7 83.5 81.7 AW-B 78.8 79 2 27 9 95 6 94.3 95.0 93.3 92.4 93 3 93 7 95.2 93 0 94.2 92.7 92.4 AW-C 72.1 47 6 17 7 91 4 85.4 86.4 84.6 81.4 66 3 91 7 90.3 85 8 90.3 86.3 74.7 AZ-A 100.9 50 1 9 5 103 4 99.2 102.2 93.5 91.5 84 2 104 1 102.1 99 9 102.4 98.0 94.5 AZ-B 94.2 110 7 102 2 90 9 64.1 91.7 90.6 91.2 101 7 99 1 98.0 90 8 93.9 89.2 88.5

Average 75.8 77 9 47 5 85 7 93.2 99.6 88.8 86.7 80 7 82 9 92.9 91 0 81.7 88.3 88.5

* Computed from three speciamens at each site.

no diflference between the low and medium gloss

enamels at any site but the high gloss enamels have

lower color retentions at all sites. When the enamels were separated into individual colors, it was found

that only the white, black, and light green enamels were produced in more than one gloss range. Study

of the gloss-retained values for these colors (bottom

of table 5 ) indicated no consistent correlation between

color retention and initial gloss.

3.6. Effect of Coating Thickness

The average color retention for the one- and twocoat enamels (top part of table 6) indicates a differ- ence in these systems. However, since the enamel

colors weather differently, the only valid comparison

is between white enamels, the only color produced in both one- and two-coat forms. This comparison is given in the lower part of table 6. Although the

5
Table 3. Color-retention data for enamels exposed for three years in the 1964 exposure test of porcelain enamels on aluminum

Enamel

Average color retention * For enamels exposed at:^

Kure Beach New York Washington Los Angeles Montreal

6-Mo. 1-Yr. 3-Yr. 6-Mo. l-Yr. 3-Yr. 6-Mo. 1-Yr. 3-Yr. 6-Mo. 1-Yr. 3-Yr. 6-Mo. 1-Yr. 3-Yr.

AA-A 99.4 98.1 96.4 99.4 99 3 99 1 99 5 99 6 99 4 99.5 99.3 99 3 99 5 99 6 99.5 AA-B 99.3 98.7 96.4 99.7 99 4 98 9 99 5 99 3 99 2 99.3 99.0 99 3 99 4 99 4 99.3 AA-C 99 .0 97 0 95 .

1

99 .2 99 0 98 8 98 8 98 8 98 5 99.0 98.5 98 8 98 9 99 0 98.9 AA-D 98.3 97!o 96^4 97^9 97 4 95 8 97 8 97 9 97 2 98.2 98.8 97 6 97 8 97 8 96.2 AB-A 98.8 97.8 94.8 98.1 97 8 97 0 98 8 98 8 98 6 98.7 98.6 97 8 98 7 98 5 97.8 AB-C 99.6 99.1 99.2 99.2 99 0 98 7 99 5 99 5 99 5 99.4 99.3 99 3 99 4 99 4 99.2 AB-D 98 5 97 6 95 .8 98 .3 98 4 97 9 98 9 98 8 98 5 98.4 99.1 97 5 98 9 98 9 97.2 AC-A 99.4 98.7 96.5 99.3 99 3 99 0 99 3 99 2 99 1 99.1 98.7 99 0 98 6 99 3 99.2 AC-B 98.7 98.1 97.6 99.0 97 1 97 1 99 1 98 8 98 4 98.6 99.2 98 2 99 0 98 4 97.9 AC-C 98.3 96.9 95.1 98.7 98 4 98 3 98 6 98 6 98 7 98.9 98.8 98 2 98 9 98 9 98.0 AD-A 98.9 98.6 96.6 99.2 99 2 98 4 99 4 99 4 99 1 99.4 99.3 99 4 99 5 99 3 99.1 AD-B 99.4 98.3 95.1 99.1 99 2 99 0 99 6 99 6 99 6 99.4 99.3 99 4 99 5 99 5 99.2 AD-C 98.1 96.9 91.9 98.1 97 9 97 4 99 0 98 8 98 0 98.5 98.4 97 6 99 1 98 9 95.5 AD-D 97 3 96 0 98 .

1

96 7 96 96 9 98 1 97 4 98.4 98.9 99 0 98 8 99 1 98.1 AE-A 99.1 94.3 79.0 99.8 99 1 99 5 98 6 98 8 97 9 99.8 97.2 99 1 99 8 99 9 99.6 AE-B 98 6 89 1 73 4 99 6 99 4 99 6 99 8 99 8 98 7 99.7 99.1 99 4 99 5 99 0 99.0 AE-C 98^9 92.9 82.0 99^6 99 6 98 4 99 6 99 6 98 8 99!4 99!2 98 8 99 5 99 0 99.4 AE-D 98.6 76.6 50.3 98.9 98 2 96 4 98 0 96 4 94 3 99.4 97.2 99 0 99 7 98 4 98.1 AF-A 98.4 88.8 61.0 98.5 97 7 98 3 99 2 99 1 97 5 99.6 97.9 98 6 99 3 98 4 98.2 AF-B 99 1 88 7 84 7 99.4 98 4 95 3 98 8 99 0 96 9 99.3 99.4 99 4 99 4 99 7 99.4 AF-C 98^4 93 !l 84.6 99.3 98 I 94 I 98 3 99 I 94 Q 99^6 98.3 98 99 3 99 4 99.1 AG-B 97.6 88.2 81.7 98.4 98 5 97 0 98 6 98 7 97 2 99.3 98.1 98 0 98 9 98 5 98.9 AG-C 98 2 97 1 83 8 98 3 98 1 98 4 99 4 99 5 98 1 99.4 99.0 98 7 99 5 99 5 99.1 AH-A 97.5 93.5 85.9 97.6 97 1 95 7 98 I 97 5 96 9 97.4 96.9 95 3 97 5 97 4 95.5 AH-B 93.0 83.1 63.0 96.6 95 1 92 9 94 6 94 0 89 6 95.5 94.4 93 9 95 2 95 2 93.5 AH-C 90.1 86.3 71.0 91.5 90 7 90 1 91 9 91 5 73 4 91.9 91.4 92 7 92 8 91 8 90.1 AH-D 83 6 70 2 61 .2 95 .2 90 8 86 3 88 9 87 2 82 5 91 .0 88.4 85 8 89 7 88 1 80.8 AO-A 95.4 91.7 83.0 99.7 99 0 99 0 99 1 99 0 97 6 99.9 99.2 98 3 99 3 99 0 99.2 AO-B 99.5 97.3 87.2 99.7 99 3 99 1 99 5 99 7 98 9 99.8 99.4 99 5 99 7 99 3 99.5 AO-D 97 8 92 0 80 9 99 4 98 6 97 6 98 5 98 0 95 8 98.9 98.6 96 6 99 4 99 0 98.2 AP-A 98.7 95.2 88.4 99.4 99 5 99 5 99 4 99 2 98 1 99.3 99.3 98 9 99 5 99 3 98.8 AP-B 99.4 98.7 96.3 99.6 99 4 99 5 99 4 99 4 99 2 99.6 99.6 99 4 99 6 99 4 99.1 AP-C 99 5 98 .9 97.5 99.6 99 7 99 5 99 0 99 1 99 0 99.2 99.6 99 2 99 5 99 6 98.9 AP-D 99^1 97^1 91^7 99.5 99 3 99 2 99 Q 99 0 98 3 99^2 99^3 98 3 99 3 99 3 98.7 AR-A 99.6 99.6 99.0 99.3 99 3 98 8 99 5 99 4 99 4 99.6 99.6 99 4 99 6 99 7 99.5 AR-B 99 4 98 8 95 9 98 .8 98 7 97 9 99 6 98 7 97 9 99.6 99.6 99 6 99 7 99 7 99.3 AR-C 99!4 98!3 94.8 98^8 98 6 98 1 99 99 5 96 2 99^5 99^4 99 3 99 7 99 99.3 AS-A 98.7 96.2 91.2 99.4 99 3 99 5 99 4 99 0 97 0 99.5 99.6 98 8 99 5 99 4 98.7 AS-B 98 9 97.3 88 .7 99 .2 99 4 98 8 99 3 99 1 98 1 99.3 99.3 98 8 99 4 99 3 98.7 AS-C 99^8 99.6 96^2 99.6 99 5 99 7 99 5 99 7 99 3 99^8 99 !6 99 5 99 3 99 5 99.6 AT-A 99.0 97.4 90.6 98.9 98 8 98 0 98 9 98 9 98 2 99.1 99.3 98 6 99 1 99 I 98.8 AT-B 98 6 94 9 87 9 98 .6 98 8 98 2 98 9 99 0 98 1 97 9 97 .8 98 2 99 3 99 1 98.6 AT-C 98.7 96^2 86^2 99.7 99 .1 98 7 97 1 99 1 98 4 99^0 98.9 98 3 99 3 99 4 99.3 AU-A 99.3 99.4 98.1 99.7 99.8 98 0 99 7 99 7 99 4 99.7 99.7 99 6 99 8 99 7 99.6 AU-B 99.2 99.4 97^6 99^5 99 .4 99 1 99 6 99 6 99 0 99!8 99^7 99 5 99 8 99 6 99.4 AU-C 99.8 99.6 97.8 99.6 99.6 99.6 99 5 99 4 99 3 99.8 99.8 99 6 99 8 99 8 99.2 AW-A 99.2 98.7 95.3 99.5 99 5 99 0 99 4 99 4 98 7 99.6 99.5 98 9 99 6 99 6 99.2 AW-B 99.3 97.3 93.9 99.3 99 2 98 8 99 2 99 0 98 8 99.3 99.3 98 8 99 2 99 3 99.2 AW-C 98.9 95.9 92.6 99.4 99 .0 98.6 99 4 99 0 96 4 99.4 99.5 98 6 99 4 99 4 97.8 AZ-A 97.7 98.9 98.0 99.2 99 0 98 5 99 3 99 2 99 0 98.9 99.1 99 0 99 1 99 2 98.2 AZ-B 99.1 97.8 95.3 99.2 98 .9 98 9 99 0 98 9 98 8 98.8 98.8 99 0 99 3 99 0 99.0

Average 98.2 95.1 88.7 98.8 98.4 97.8 98 6 98 6 97 2 98.9 98.7 98.2 98.9 98.8 98.1

a Color Retention is 100 minus the color change in NBS units.

^ Computed from three specimens at each site. Table 4. Color Retention for the various colors of porcelain enamels on aluminum after three years' exposure

Enamel color Average color retention * for the enamels exposed at:

Kure Beach Washington New York Montreal Los Angeles

Red 70.3 85.6 91 .3 90.0 91.9

Black 75.6 97.0 97 .2 99.0 98.8

Dark green 83.7 97.4 98 .6 99.0 98.1

Blue 88.2 98.2 98 .3 98.9 98.4

Grev_ _ 88.7 98.1 99 .3 99.0 99.1

Yellow.. 93.9 98.0 98 .8 98.7 98.8 White 96.0 98.7 98 .1 98.3 98.5

Light green. . 94.8 98.4 98 .9 99.1 99.2 Browu 97.8 99.2 98 .9 99.4 99.6

* Color retention is 100 minus the color change in NBS units.
AVERAGE COLOR RETENTION FOR THE ENAMEL EXPOSED AT THE DIFFERENT SITES: 111 KURE beach; I2l WASHINGTON; C-D NEW YORK; 141 MONTREAL, 151 LOS ANGELES.

10 0 I — —

BROWN Lt, GREEN WHITE YELLOW GREY BLUE Dk. GREEN BLACK RED ENAMEL COLOP

Figure 3. Comparison of the color retention of the nine different colors included in this test program.

Table 5. Effect of initial gloss on the color retention of porcelain enamels on aluminum

Average color retention for the enamels exposed at: Initial gloss

Kure Beach Washington New York Montreal Los Angeles

All Enamels

Low__ 92.8 97.8 98.0 98.8 98.8 Medium _ _ _ 92.9 98.5 98.5 98.7 98.8

High 83.4 95.6 97.0 97.2 97.6

Colors produced in more than one gloss range

White

Low _ 95.9 98.0 97.3 97.7 97.7 Medium 95.5 99.0 98.1 98.2 98.2 High 96.3 98.7 98.3 98.5 98.7

Black

Low__ 82.8 97.7 97.7 99.0 98.4 Medium. 84.7 96.9 95.8 99.4 99.4

High 71.7 96.9 97.7 99.1 98.9

Light green

Low __ 96.6 97.8 98.3 99.5 99.4 Medium. 93.5 98.8 99.4 99.1 98.5

* Color retention is 100 minus the color change in NBS units.

7
Table 6. Effect of one and two coats on the color retention of porcelain enamels on aluminum

Number of coat3 Average color retention * for the enamels exposed at:

Kure I3each Washington New York Montreal Los Angeles

All Enamels

One 81 8 95.6 96.7 97.1 97.5 Two 94 5 98.5 98.6 98.8 98.9

White Enamels Only

One.- _ 96 4 98.2 98.7 98.6 98.4 Two 95 5 98.0 98.6 98.1 98.1

^ Color retention is 100 minus the color change in NBS units.

1 . . 1 1 1 1

• • • • "

1

1 1

•

1

-

•

® • ^^--^..^^^

• • • •

•

•

• • •

" (A) •

Kure Beach

1 1 ! 1 1

1

1 1 1

2 4 6 8 10 12 14

BOILING ACID SOLUBILITY, mg/in.^

16 18 20 22

' = « 1 « e* 'c. I« 1 1 1 o

1 •1

« • "«

•

•

• • -

" (B)

Los Angeles

1 1 i

0

1 1 1 _L . I...

BOILING ACID SOLUBILITY, rag/in.^

Figure 4. Correlation' between boiling acid solubility test and color retention for the enamels

exposed at (a) Kure Beach, (b) Los Angeles.
diflFerences in color retention of the one- and two-coat systems are small, less than one NBS unit at all sites, they may prove significant after longer exposure

times. The one-coat enamels had consistently higher

color retentions than the two-coat enamels.

3.7. Correlation with Accelerated Tests

The correlation between color retention and the boiling acid solubility test is illustrated for Kure Beach

and Los Angeles in figure 4. It can be seen that at the mild site, Los Angeles, the color retention remains

high regardless of the boiling acid solubility, while

at the severe site, Kure Beach, the color retention may

be as low as 70 or as high as 98 for approximately

the same value of boiling acid solubility.

The relatively poor correlation between color re- tention and boiling acid solubility led to the development of another test which could be useful in pre- dicting the color retentions of these enamels. The new

test uses the same apparatus as the boiling acid solubility test but the reagents and time of treatment were

changed. Fifty ml of 12.5 percent aqueous cupric

chloride solution are substituted for 150 ml of 6 per- cent citric acid. The specimen surface is exposed to boiling cupric chloride solution for one hour. The

treated area is then rinsed with 10 ml of a 1 percent

solution of oxalic acid to remove any green copper

stains that may have accumulated. The specimen is removed from the apparatus, washed with a mild

detergent solution, rinsed with tap water, distilled

3 60 -

COLOR RETENTION AFTER CUPRIC CHLORIDE TREATMENT

COLOR RETENTION AFTER CUPRIC CHLORIDE TREATMENT

Figure 5. Correlation between boiling cupric chloride treatment and color retention tor the enamels exposed at (a) Kure Beach, (b) Los Angeles.
water, and alcohol, and allowed to dry in a near verti- cal position. After the specimens are dry the color

difference between the tested and untested portions of

the specimens is determined and is used as a measure

of the specimens' weather resistance. These values are

plotted as a function of the color-retention values after three years' exposure in figure 5. The correlation is improved over that obtained for the boiling acid

solubility as indicated by the smaller residual standard

deviations (see table 7) for the fits of the least squares

lines. Although the correlation between the color re- tention and the results of the boiling cupric chloride

test is better than that with the boiling acid solubility

test, it is felt that longer exposure times are necessary

before any recommendations for specification changes

are made. This increased exposure time is necessary because the color retention after three years' exposure

of the enamels that passed the boiling acid solubility

test is adequate (more than 94) at all sites except

Kure Beach.

Table 7. Comparison of the residual standard deviations ^ for the least squares fits for boiling acid solubility and cupric

chloride tests versus color retention of exposed enamels

Exposure site

Kure Beach. Washington New York„ _ Montreal

Los Angeles

Residual standard deviation of fit

Boiling acid

solubility Cupric

chloride

10.24 8.14

4.39 3.11 2.45 1.48 3.00 1.85 2.23 1.20

* These residual standard deviations were computed hy a subroutine called *'Ortho", Walsh^ P., Ortho, Commun. Assoc. Computing Mach. 5 511-13 (1962).

3.8. Correlation with Enamels in a Previous

Exposure Test

Kure Beach, Washington, and Los Angeles are three

sites common to both the current test and a test ini- tiated in 1956 [11]. The average color-retention data

for the enamels exposed at these sites in both tests are included in table 8. These data indicate that the enamels in the current test are as durable as the early

porcelain enamels on aluminum at all sites, and at the milder sites, Washington and Los Angeles, are as good

as the acid resistant enamels on steel. Since it was

shown (sec. 2.4) that the initial color has a marked

effect on the color retention, only the white, yellow,

and green enamels on aluminum were used in this comparison.

Table 8. Comparison of the color retention of the enamels in

this test with those in an earlier test

Exposure

test Type of enamel

Average color retention * for enamels exposed at:

Kure Beach Washington Los Angeles

1956 b 1956 b

1964

Acid resistant, on steel On aluminum, (green, white, and yellow) On aluminum, (green, white, and yellow)97.9

93.3

94.0

98.2

97.1

98.4

98.4

97.1

98.7

a Color retention is 100 minus the color change in NBS units,

b Data taken from Reference 11.

3.9. Nature-Tone Enamels on Aluminum

Seven nature-tone or mat enamels on aluminum

were added to the test program after the one-year

inspection. The initial gloss, color, and thickness of

these enamels are presented in table 9 while the color- retention and percentage gloss-retained data for these enamels are presented in table 10. These data indicate good gloss and color retention for most enamels at

all sites. One enamel, AM-7, spalled enough to constitute failure at all sites.

Table 9. Initial data for nature-tone enamels on aluminum

Enamel Color

45-deg » Specular

gloss

Thickness b Boiling " acid

solubility

Acid

spot

test

mils mg/in^ AM-2 Lt. brown _ 19.5 2.3 10.0 A

AM-3 Blue _ 10.5 2.6 13.0 A

AM-4 Lt. blue 7.6 2.1 9.3 A

AM-5 Green 17.4 2.7 13.6 A

AM-6 Lt. green _ 16.5 3.1 8.0 A

AM-7 Gray 11.2 2.1 11.7 B 'AM-8 Lt. gray 45.3 2.0 15.7 B

» The 45-deg specular gloss was measured in accordance with ASTM designation C-346.

b The thickness was measured in accordance with ASTM designation E-376.

c The boiling acid solubility was determined in accordance with ASTM designa*

lion €-283.

d The acid spot test ratings were determined in accordance with ASTM designation C-282.

Table 10. Gloss and color retention of nature-tone enamels on aluminum after two years* exposure

Enamel

Average color retention * for enamels exposed at; Average percentage gloss retained for enamels exposed at:

Kure Beach Washington New York Montreal Los Angeles Kure Beach Washington New York Montreal Los Angeles AM-2 92.9 97.1 98.9 97.5 98.8 76.8 91.5 119.2 87.3 85.7 AM-3 92.5 95.1 99.3 98.1 98.8 74.0 88.8 103.0 95.2 92.9 AM-4 95.2 98.9 99.3 99.2 99.1 79.9 82.4 108.3 105.6 103.0 AM-5 96.2 99.0 99.7 98.3 99.6 88.0 92.5 113.1 95.1 95.1 AM-6 96.4 98.9 99.5 99.7 98.9 77.3 89.9 110.7 91.4 85.2 AM-7 91.3 98.2 99.4 99.3 98.7 76.6 77.3 155.3 88.9 87.7 AM-8 93.9 97.8 98.7 97.7 98.6 65.0 93.0 84.9 84.9 82.2

* Color retention is 100 minus the color change in NBS units.

10
4. Summary

The 3-year inspection of the enamels included in the 1964 Exposure Test of Porcelain Enamels on Alumi- num indicated that:

1. The color retention of all colors except reds was good at all sites except Kure Beach.

2. There was no significant spalling on any of the enamels originally included in this test. One

nature-tone enamel added to the test after one

year's exposure did spall.

3. The atmosphere at Kure Beach was extremely

aggressive on many of the enamels included in

this test. 4. There were no significant effects attributable

either to initial gloss or coating thickness.

5. The correlation between color retention and boil- ing acid solubility was poor.

6. The results of the boiling cupric chloride test correlated better with color retention than did those of the boiling acid solubility test.

5. References

[1] Rushmer, M. A., and Burdick, M. D., Weather Resist- ance of Porcelain Enamels: Effect of Exposure Site and Other

Variables after Seven Years, Nat. Bur. Stand. (U.S.), Bldg.

Sci. Ser. 4, 16 pages (May 1966).

[2] Resistance of Porcelain Enameled Utensils to Boiling

Acid, C-283 ASTM Book of Standards, Pt. 13, (1968).

[3] Acid Resistance of Porcelain Enamels (Citric Acid

Spot Test), C-282 ASTM Book of Standards, Pt. 13, (1968).

[4] Recommended Practice for Measurement of Coating Thickness by Magnetic Field or Eddy Current (Electromagnetic) Test Methods, E-376 ASTM Book of Standards, Pt. 3, (1%8).

[5] Gloss of Ceramic Materials, 45-Deg. Specular, C-346, ASTM Book of Standards, Pt. 13, (1968).

[6] Instrumental Evaluation of Color Differences of Opaque

Materials, D-2244, ASTM Book of Standards, Pt. 21, (1968).

[7] Potter, A., Using an electronic computer to reduce weathering data. Proceedings of the Porcelain Enamel In- stitute Forum 20, 73 (1958).

[8] Test for Spalling Resistance of Porcelain Enameled Aluminum, C-486, ASTM Book of Standards, Pt. 13, (1968).

[9] Natrella, M. G., Some tests v^hich are independent of the form of distribution, Chapter 16, Experimental Statistics, Nat. Bur. Stand. (U.S.), Handb. 91 (August 1963).

[10] Recommended Specification for Architectural Porcelain Enamel on Aluminum for Exterior Use, PEI: ALS-105, Porcelain Enamel Institute, ( 1969)

.

[11] Moore, D. G., and Potter, A., Effect of Exposure Site on Weather Resistance of Porcelain Enamels Exposed for Three Years, Nat. Bur. Stand. (U.S.), Monogr. 44, 13 pages

(April 1962).

All. S. GOVERNMENT PRINTING OFFICE : 1970 392-251/156

11

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