NBS MONOGRAPH 44

Effect of Exposure Site on

Weather Resistance of

Porcelain Enamels

Exposed for Three Years

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U.S. DEPARTMENT OF COMMERCE

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UNITED STATES DEPARTMENT OF COMMERCE • Luther H. Hodges, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Effect of Exposure Site on

Weather Resistance of

Porcelain Enamels

Exposed for Three Years

Dvvight G. Moore and Alan Potter

National Bureau of Standards Monograph 44

Issued April 10, 1962

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. - Price 15 cents
Contents

Page

1. Introduction 1 2. Types and sources of enamels 1 3. Description of specimens and method of mounting 2

4. Exposure sites 2

5. Results 3

5.1. Ease of cleaning 3

5.2. Corrosion protection 3

5.3. Changes in gloss 3

5.4. Changes in color 3

6. Comparison of exposure sites 7

7. Comparison of enamel types 9

8. Effect of exposure angle 10

9. Correlation of weather resistance with citric acid spot test 11

10. Copper sulfate test for predicting color stability of red and yellow

enamels 11

11. Discussion 12

12. Summary . 12

13. References 13

11
Effect of Exposure Site on Weather Resistance

of Porcelain Enamels Exposed for Three Years

Dwight G. Moore and Alan Potter

An exposure test of porcelain-enameled steel and aluminum specimens is being con- ducted jointly by the Porcelain Enamel Institute and the National Bureau of Standards. The exposure sites are Dallas, Tex.; Los Angeles, Calif.; New Orleans, La.; Pittsburgh,

Pa.; Washington, D.C.; and two sites at Kure Beach, N.C. The present report gives the results of the third-year inspection. Changes in gloss

and color were taken as criteria of weathering. Based on averages for all enamels, the

80-ft site at Kure Beach caused the greatest change in gloss and color, while the conditions

at Dallas, Los Angeles, and New Orleans caused the least change. The conditions at Washington, Pittsburgh, and the second Kure Beach site (800 ft from the ocean) were

of intermediate severity. Comparison of the gloss and color changes with data obtained

by the National Air Sampling Network indicated that air pollution by acidic contaminants was a factor in site severity.

A direct relation existed between acid resistance and weather resistance. This rela- tion was apparent, however, only when averages were considered. There were individual exceptions within groups of enamels of the same general type. In addition, enamels of

different types, such as aluminum and steel enamels, having the same acid resistance

(citric acid spot test) did not necessarily show the same weather resistance. Further, some red and yellow enamels with good acid resistance showed poor color stability. It was found, however, that this poor stability could be predicted by a specially developed

cupric sulfate test. As a group, the regular glossy enamels for steel showed the best weather resistance among the various types tested.

1. Introduction

The use of porcelain enamel as an exterior finish for many types of building structures has been

expanding rapidly during the past decade [l].

1 The factors responsible for this increase include:

(a) the trend in the building industry towards

curtain wall construction, (b) the emphasis on

color in modern architecture, (c) the ease with

which most porcelain enamel finishes can be

cleaned, and (d) the excellent weather resistance of

many porcelain enamels.

An earlier investigation conducted by the

National Bureau of Standards [2] provided information on weather resistance for porcelain enamels

that were in common use when the exposure tests were started (1940). After World War II, several new types of enamel were introduced.

These included (a) enamels for aluminum, (b)

"low-temperature" enamels for steel, and (c) steel enamels opacified with titanium dioxide.

The present investigation, initiated in 1956, is a

joint effort of the Enameled Metals Laboratory at the National Bureau of Standards and the Porcelain Enamel Institute, working through its Research Associateship at the Bureau. The goals are twofold: (1) to evaluate the weather resistance

of new types of porcelain enamel that have been

introduced during the past 15 yr, and (2) to

* Research associate, Porcelain Enamel Institute. Present address: Graduate School, Mississippi State University, State College, Mississippi.

1 Figures in brackets indicate the literature references at the end of this Monograph.

develop reliable tests for predicting weather

resistance.

The first report of the current investigation was

published in 1957 [3]. This was not a complete

report, but was concerned almost entirely with

observations on the red and yellow screeningpaste enamels after the first year of exposure.

The present report describes the condition of all of the porcelain enamels after exposure for 3 yr.

2. Types and Sources of Enamels

The 28 types of enamel used in the test were

furnished to 21 fabricators of architectural enamel

parts by seven companies who manufacture

enamel frits. 2 The fabricators then applied the

enamels to the test specimens. A later table

(table 3) includes coded identification of the frit suppliers and fabricators. Minor variations in composition probably occurred in the same enamel

type as furnished by different frit companies.

Likewise, in many cases, different fabricators

applying the same enamel may not have achieved an identical finish because of minor variations in

milling and firing. If these variations in history of

the specimens are taken into consideration, there were, in effect, 94 enamels under study, of which

80 were applied to sheet steel and 14 to sheet

aluminum.

2 Frit is the principal ingredient used in preparing porcelain enamel. It is formed by melting suitable raw materials and then quenching the molten

mass, usually in water.

i
3. Description of Specimens and

Method of Mounting

The type of specimen being used in the tests is shown in figure 1. A large supply of 18-gage

metal blanks with this configuration were obtained

and forwarded to the fabricators. The fabricators,

in turn, applied each porcelain enamel, as specified,

to about GO specimens. Twenty-one of these were used for exposure testing (three at each site),

while the remainder were kept in dry storage for later use in development of accelerated tests.

The specimens are mounted loosely in ceramic

insulators which are fastened to the metal

stretchers of the supporting racks. The racks are constructed of aluminum alloy except for two

seashore locations, where Monel metal is used.

The lacks face south except at the Kure Beach -SO

ft station, where they face the ocean (east-southeast). Figure 2 shows a typical installation.

The normal exposure angle for the specimens is 45°. However, at Washington an additional rack

is installed in which a representative group of

specimens is exposed vertically.

4. Exposure Sites

The seven exposure-test locations and the

general exposure conditions that each site repre- sents are given in table 1 . The sites were selected

as being representative of the various exposure

conditions in different parts of the I nited States. The racks at five sites are located in the commercial area of the city; the remaining two are in

a rural sea coast location.

Table 1. Exposure Test Locations

City Exposure site Exposure conditions represented

Dallas, Tex

Kure Beach, N.C

Kure Beach, N.C

Los Angeles, Calif- New Orleans, La

Pittsburgh, Pa... . .. Washington, D.C

Roof, U.S. Post Office Ground, 80 ft from beach.. Ground, 800 ft from beach.

Roof, U.S. Post Office

Roof, U.S. Post Office

Roof, U.S. Post Office

Roof, Industrial Bldg., National Bureau of Standards.

Texas, commercial. Temperate, sea spray. Temperate, sea air. Southern Calif., commercial.

Semitropieal, commercial. Temperate, commercial. Do.

INCHES Figure 1. Exposure test specimen.

The weather data for the actual period of exposure are given in table 2.
Table 2. Weather data for the 3-yr exposure period From U.S. Weather Bureau Records.

City Exposure period Average

annual

rainfall

Average annual

sunshine

Average

temperature

Dallas, Tex June 1956-June 1959 May 1956-May 1959. June 1956-June 1959. June 1956-June 1959. Julv 1956-Julv 1959__ Aug. 1956-JulV 1959.

In.35.3

54.4

12.1 66.7 33.8

38.8

Hr.

2. 821

2. 873

3. 367

2, 446 1.807

2. 539

°F.

66.0

63.0 66.4

69.8

53.2

57.0

Kure Beach, X.C

Los Angeles, Calif. __ New Orleans, La

Pittsburgh, Pa

Washington. D.C

5. Results

After exposure for 3 yr, all specimens were removed and returned to Washington, where

they were evaluated for ease of cleaning, corrosion

of base metal, changes in gloss, and changes in

color. The specimens were then returned to the

racks for further exposure.

5.1. Ease of Cleaning

The ease with which specimens could be cleaned

after exposure for 3 yr varied with the exposure

location. The specimens from Dallas, Washington, and the two Kure Beach sites could be

cleaned easily by washing with a one percent by

weight solution of trisodium phosphate. The

same treatment removed almost all of the adhering

dirt film from the specimens exposed at Los

Angeles and New Orleans and, because the small

amount that remained did not detract from the

overall appearance of the enamels, these specimens were given no further cleaning treatment. Most of the Pittsburgh specimens, on the other

hand, could not be cleaned satisfactorily by the

washing treatment. They were covered by a

thin, but tightly adherent, deposit which appeared

to consist mostly of fly ash and soot. The ease with which the deposit coidd be removed varied

with the type of specimen surface. Cleanability

ratings were assigned to the various enamels from

the Pittsburgh site and these ratings were then

compared to both the initial 45° specular gloss

and the 45° gloss after 3 yr of exposure. The

following summarizes the results

:

Cleanability

rating a No. of spec- imens aver- aged

Average and

initial 45°

gloss

Average 3-yr 45° gloss

1 _ . 26

64

4

58. 8

49. 0

67. 1

41. 8 34 4

28. 8 2 . . 3

» Xo. 1—cleanable by washing with a trisodium phosphate solution; No. 2

cleanable by scouring with a commercial scouring powder; Xo. 3—not completely cleanable by scouring.

As might be expected, the ease of cleaning of the

Pittsburgh specimens was not related to the

initial gloss but rather to the gloss of the surface

after 3 yr of exposure. However, the correlation was good after 3 yr only when averages were considered and many individual exceptions to the

correlation were observed.

5.2. Corrosion Protection

Xo serious corrosion of the base metal was noted on any of the specimens after exposure. However,

a mild rusting at edges and at areas of poor

coverage on the backs was observed on some of

the enameled steel specimens that had been ex- posed to the sea air conditions at Kure Beach.

The only undamaged specimens 3 that showed

evidence of corrosion on the face side at any of the

sites were those to which the 1,000 °F steel enamels

had been applied (Y-l and Z-l in table 3). A

few scattered pinholes were present in these enamels. At both Kure Beach sites rust stains

appeared on small areas of the enamel surface

adjacent to the pinholes and these stains could

not be removed completely even by vigorous

scouring.

5.3. Changes in Gloss

Specular gloss measurements were made with a Gardner 45° Glossmeter [4] which was calibrated

and operated in accordance with the ASTM Tentative Method of Test for 45-Deg Specular Gloss

of Ceramic Materials [5]. Measurements were made at four fixed locations at the center of each

specimen and compared with similar measure- ments made at the start of the investigation.

The data were expressed as the percentage of

initial specular gloss retained.

The specimens were cleaned prior to measure- ment with a 1-percent-by-weight aqueous solution of tri-sodium phosphate. While this treat- ment was not always effective in removing the

last remnants of adhering dirt particles (see 5.1),

the surfaces were nevertheless believed to be of

comparable cleanliness to a "cleaned" architectural installation. Except for the Pittsburgh

specimens (see 5.1), scouring was not used as a

cleaning treatment because the protective surface

films [2] would have been removed, and the subsequent weathering behavior of the enamel might

have been changed significantly.

The results of the gloss measurements are given

in table 3.

5.4. Changes in Color

A Hunter Color-Difference Meter [6] was used

to measure the change in color. Measurements

were made on each specimen at the beinning of the investigation and again after exposure. The

color difference in XBS units [7] was computed

from these measurements and expressed in terms

3 A few specimens were damaged at the Pittsburgh site when one of racks overturned during a strong windstorm.

3
Table 3. Optical data and acid resistance spot test ratings of enamels

AverPercentage of initial gloss retained (Gr) and color retention (Cr) after exposure

for 3 yrs at —b-~

Citric Specimen

identification

Fabricator of

speci- mens

Frit supplier

H eporl e(i firint; temperatureage

initial spec- ular

gloss

Kure BeachSoft

Kuie Beach—

800 f!

New

Orleans Dallas LosAngeles

Pitts- burgh « Washington Average

acid

spottest

rat- ing <• Gr Cr Gr Cr Gr Cr Gr Cr Gr Cr Gr Cr Gr Cr Gr Cr

TITANIUM WHITE, GLOSSY ENAMEL ON STEEL—KESISTANT TO ACIDS AND ALKALIES

°F

A-l 1 a 1,540 64 78.2 97.8 77.7 99.1 88.1 98.4 90.0 98.2 93.8 98.8 81.3 98.0 85.3 98.4 94.9 98.4 AA

A-2 2 a 1,520 60 84.5 99.1 80.0 99.4 90.0 99.2 91.0 99.0 95.9 98.8 81.2 97.4 88.2 99. 1 87.7 98.9 AA

A-3 3 b 1,525 71 75.4 98.7 98.7 99.4 90.2 99. 7 91.8 99.5 98.8 98.6 71.9 98.5 94.8 98.9 88.8 99.0 AA

A 4 4 b 1,430 62 84.3 98.4 85.5 98.

1

87.8 98.1 82.1 98.2 83.6 98.2 73.3 98.3 82.0 98.0 84.9 99.2 AA

Average 80.6 98.5 85.5 99.0 89.0 98.8 89.5 98.7 93.0 98.6 76.9 98.0 87.6 98.6

TITANIUM WHITE, GLOSSY ENAMEL ON STEEL—RESISTANT TO ACIDS BUT NOT TO ALKALIES

B-l 5 a 1.450 60 74.9 97.7 80.4 98.8 86.9 98.1 87.7 98.5 88.8 98.4 79.6 96.7 75.1 98.7 81.9 98.1 B

B-2- 6 a 1, 425 63 72.7 97.3 83.7 98.6 86.1 97.5 87.6 98.4 91.1 98.5 78.0 96.8 70.5 97.6 81.4 97.8 B

B-3. 7 b 1.450 60 69.5 97.4 76.4 99.3 88.5 97. S 90.0 98.6 90.2 99.0 77.3 97.0 80.9 98.0 81.8 98.2 A

B-4 8 b 1,430 60 66.2 97.9 73.1 99.0 86.5 98.7 84.6 98.7 92.3 98.4 74.3 97.0 79.8 98.7 79.6 98.3 B

70.8 97.6 78.4 98.9 87.0 98.0 87.5 98.6 90.6 98.6 77.3 96.9 76.6 98.2

ZIRCONIUM WHITE, OLOSSY ENAMEL ON STEEL—RESISTANT TO ALKALIES BUT NOT TO ACIDS

C-l 9 a 1,430 65 42.5 97.7 57.

1

98.8 73.6 97.9 75.1 99.0 74.4 97.9 40.8 93.9 31.6 98.0 56.4 97.6 C

C-2_ 8 a 1,540 70 34.4 97.5 55.6 98.7 74.4 98.2 74.2 99.2 75.1 98.0 50.2 94.2 37.4 98.2 57.3 97.7 C

C-3 1 b 1, 520 64 18.8 98.0 33.4 98.7 US II 98.2 69.0 99.0 75.4 97.5 41.2 92.0 36. 7 98.4 48.9 97.4 D

C-4 2 b 1,500 65 19.5 97.7 31.

1

98.4 66.1 98.4 69.0 99.7 70.2 97.5 39.3 92.

1

31.2 97.6 46.6 97.4 D

Average 28.8 97.7 44.3 98.6 70.5 98.2 71.8 99.2 73.8 97.7 42.9 93.0 34.2 98.0

RED, GLOSSY ENAMEL ON STEEL—ACID-RESISTANT TYPE

D-l 10 c 1, 500 40 66.3 93.8 78.1 96.7 87.4 95.8 90.8 95.8 97.1 96.8 81.0 96.6 75.2 95.9 82.3 95.9 C

D-2 11 c 1,520 56 70.

1

97.6 80.7 98.1 86.3 98.7 78.4 98.6 83.8 95.0 73.5 96.8 78.1 99.1 78.7 97.7 A

D-3 12 d 1.480 62 97.2 96.2 72.7 98.9 87.0 99.4 86.6 99.5 87.3 99.

1

74.

1

96.8 76.2 98.9 83.0 98.4 AA

D-4 13 d 1,490 62 89.0 97.5 68.5 98.9 87.8 99.2 88.1 99.0 92.2 98.1 75.8 96.7 72.1 98.8 81.9 98.3 AA

80.6 96.3 75.0 98.2 87.1 98.3 86.0 98.2 90.1 97.2 76.1 96.7 75.4 98.2

RED, LOSSY GENAMEL ON STEEL—NON-ACID-RESISTANT TYPE

E-l _ 12 c 1,510 53 55.1 98.0 67.2 99.

1

80.8 98.8 79.8 99.0 86.2 99.0 69.8 97.4 71.7 99.5 73.0 98.7 C

E-2 13 c 1.510 54 55.

1

98.

1

67.8 98.8 82.8 99.

1

SO S 99.4 86. 7 98.6 70.5 96. 0 70.8 97.6 73.5 98.2 C

E-3 10 d 1,520 56 59.0 97.3 67.0 98.

1

77.6 98.9 78.4 98.4 85.0 97.8 59.5 93.

1

44.9 90.8 67.3 96.3 D

E-4 _ 14 d 1,480 55 54.2 98.4 64.0 98.8 75.4 99.4 79.8 99.5 88.3 99.4 68.7 94.7 74.2 99.1 72.1 98.5 D

55.8 98.0 66.5 98.7 79.2 99.0 79.7 99.

1

86.6 98.7 67.1 95.3 65.4 96.8

RED, GLOSSY SCREENING PASTE ENAMEL ON STEEL—ACID-RESISTANT TYPE

(Predicted by manufacturers as being likely to have good weather resistance)

F-l 5 a 1.500 63 23.

1

68.6 46.7 76.1 73.6 82.2 70.6 90.7 78.1 81.8 70.3 83.4 44.1 81.5 58.1 80.6 C

F-2 15 a 1,500 61 50.5 68.9 63. 2 79.0 79.2 87.2 76.2 94.6 83.9 86.

1

70.2 86.

1

59.2 87.4 68.9 84.2 A

F-3 16 a 1.500 61 43.4 70.3 63.5 79.1 79.5 sr. s 74.7 92.6 82.2 84.1 74.3 85.8 44.2 85.6 66.0 83.3 B

F-4 _ 17 a 1, 500 62 22.9 71.6 52.0 77.7 77.3 80.6 73.7 91.2 82.4 80.4 70.4 83.3 45.6 82.2 60.6 81.0 C

Average 35.0 69.8 56.4 78.0 77.4 84.0 73.8 92.3 81.6 83.1 71.3 84.6 48.3 84.2

RED, GLOSSY SCREENING TASTE ENAMEL ON STEEL—ACID-RESISTANT TYPE

(Predicted as being likely to have poor weather resistance)

o F

FA-1 5 a 1,500 52 36.0 53.3 70.6 50.7 73.2 50.4 71.3 77.5 82.6 63.8 71.8 45.8 55.3 45.4 65.8 55.3 C

FA-2 15 a 1,500 50 51.8 48.3 78.6 54.4 77.1 54.9 75.8 83.2 93.8 72.0 75.4 49.9 76.4 50.3 75.6 59.0 B

FA-3.. 16 a 1,500 52 51.2 49.3 81.8 51.4 82.1 52.2 75.7 82.5 87.6 67.0 76.4 52.5 65.9 48.9 74.4 57.7 B

FA-1 17 a 1,500 53 21.2 53.9 57.1 50.1 75.5 50.4 74.7 75.2 82.6 62.3 67.7 48.8 56.2 49.0 62.2 55.7 C

Average 40.0 51.2 72.0 51.6 77.0 52.0 74.4 79.6 86.6 66.3 72.8 49.2 63.4 48.4

YELLOW, GLOSSY SCREENING PASTE ENAMEL ON STEEL—ACID-RESISTANT TYPE

(Predicted as being likely to have good weather resistance)

G-l _ 5 b 1, 500 39 78.4 91.5 71.9 92.3 79.6 93.2 79.5 96.0 89.0 90.6 79.8 91.2 71.5 94.4 78.5 92.8 A

G-2-... 15 b 1,500 46 52.5 84.9 66.2 85.0 72.7 88.6 81.7 95.1 80.0 87.5 77.3 90.7 69.9 89.9 71.5 88.8 AA

G-3 - . 17 b 1,500 40 60.7 90.0 71.2 92.7 82.2 93.2 78.3 95.9 91.0 90.8 79.2 93.4 67.8 94.2 75.8 92.9 A

G-4 16 b 1,500 45 61.7 89.4 72.3 89.7 80.3 92.4 78.4 96.0 77.5 91.7 64.6 94.

1

68.6 93.8 71.9 92.5 A

63.3 89.0 70.4 89.9 78.7 91.8 79.5 95.8 84.4 90.2 75.2 92.4 69.4 93.

1

See footnotes at end of table. 4
Table 3. Optical data and acid resistance spot test ratings of enamels—Continued

AverPercentage of initial gl oss retained (Gr) and color retention (Cr) after exposure

for 3 yrs at —b—

Citric Specimen

identification

Fabricator of speci- mens

Frit supplierReported

firing temperature

age

initial spec- ular

gloss a

Kure

Beach

80 ft

Kure

Beach

800 ft

New

Orleans Dallas LosAngeles

Pitts- burgh r Washington Average

acid

spottest

rat- ing d Gr Cr Gr Cr Gr Cr Gr Cr Gr Cr Gr Cr Gr 1 Cr Gr Cr

YELLOW, GLOSSY SCREENING PASTE ENAMEL ON STEEL—ACID-RESISTANT TYPE

(Predicted as being likely to have poor weather resistance)

GA-1 5 b 1,500 34 67.0 81.2 76.2 78.3 78.6 80.9 79.7 90.0 90.0 85.2 69.6 83.1 74.8 79.9 76.6 82.6 A

GA-2 15 b 1,500 45 56.8 78.9 64.3 75.3 72.6 80.3 77.2 90.9 73.3 84.7 68.3 82.7 76.4 80.4 69.8 81.9 A

GA-3 16 b 1,500 37 64.2 79.9 70.6 77.8 76.4 82.6 88.7 91.0 92.7 86.2 73.7 85.0 74.1 81.2 77.2 83.4 A

GA-4 17 b 1,500 32 67.9 80.4 75.1 77.9 81.2 82.2 91.6 89.8 103.2 84.8 78.6 83.3 75.6 81.2 81.9 82.8 A

Average - -.. 64.0 80.1 71.6 77.3 77.2 81.5 84.3 90.4 89.8 85.2 72.6 83.5 75.2 80.7

BLACK, GLOSSY ENAMEL ON STEEL—ACID-RESISTANT TYPE

JBC-1 12 e 1,500 66 74.1 98.4 84.7 98.3 81.5 99.1 73.9 99.2 79.3 99.

1

59.8 97.6 70.9 98.0 74.9 98.5 AA

H-2 13 e 1, 510 66 77.2 98.4 76.9 98.

1

82.5 98.9 75.5 99.

1

80.0 99.2 60.3 97.7 70.5 98.2 74.7 98.5 A

H-3 14 c 1,480 60 87.1. 97.8 83.7 99.2 84.2 98.6 86.4 98.7 90.7 99.3 71.5 95.9 80.4 99.5 83.4 98.4 A

H-4 10 c 1, 500 61 65.7 95.9 69.3 98.4 84.8 98.3 88.0 98.1 94.6 98.9 73.1 95.5 84.0 98.2 79.9 97.6 A

Average ... 76.0 97.6 78.6 98.5 83.2 98.7 81.0 98.8 86.2 99.1 66.2 96.7 76.4 98.5

BL^CK, GLOSSY ENAMEL ON STEEL—NON-ACID-RESISTANT TYPE

K-l 12 e 1, 500 62 59.3 98.5 49.2 99.0 77.0 99.2 74.1 99.2 79.6 99.2 66.2 95.9 72.7 98.6 68.3 98.5 C

K-2 13 e 1,510 61 48.4 97.4 45.8 99.0 76.8 98.7 75.0 98.8 80.8 98.9 69.0 96.0 72.5 98.4 66.9 98.2 D

K-3 14 c 1,480 57 48.4 92.7 54.0 96.6 78.5 97.0 77.0 98.8 85.4 97.2 71.5 97.7 73.8 95.8 69.8 96.5 D

K-4 10 c 1, 500 53 62.1 91.6 71.2 95.1 77.3 91.0 76.1 95.6 79.8 90.6 70.6 93.0 65.1 81.9 71.8 91.2 D

Average 54.6 95.0 55.0 97.4 77.4 96.5 75.6 98.1 81.4 96.5 69.3 95.6 71.0 93.7

TITANIUM PASTEL YELLOW, GLOSSY ENAMEL ON STEEL—ACID-RESISTANT TYPE

lr-1 6 b 1,525 62 72.0 98.4 78.1 97.9 85.7 98.4 86.4 98.2 86.1 98.3 75.3 97.6 79.3 98.3 80.4 98.2 A

L-2 7 b 1,525 60 72.8 98.5 74.0 98.0 86.2 98.8 87.3 98. 6 89.2 98. 7 74.9 97.3 79.2 98.7 80.5 98.4 A

L-3 11 c 1,470 67 52.8 98.8 69.8 95.5 84.4 99.3 84.4 98.9 84.7 99.2 74.9 97.9 79.5 98.8 75.8 98.3 A

L-4 12 c 1,480 62 84.3 98.4 85.5 98.1 87.8 98.1 82.1 98.2 83.6 98.2 73.3 98.3 82.0 98.0 82.7 98.2 AA

Average 70.5 98.5 76.8 97.4 86.0 98.6 85.0 98.5 85.9 98.6 74.6 97.8 80.0 98.4

BLUE, GROUND-COAT ENAMEL ON STEEL—ACID-RESISTANT TYPE

M-l 18 a °F

1,580 57 72.6 99.0 76.5 99.0 83.4 99.4 78.8 99.2 84.3 98.9 69.1 98.3 79.3 98.8 77. 7 99.0 A

M-2. 8 a 1, 580 57 65.5 97.8 76.1 98.8 83.8 99.0 78.5 99.1 81.

1

98.5 73.7 95.0 82.1 99.0 77.2 98.2 A

M-3„. 7 d 1,540 57 78.0 99.1 73.4 96.5 88.9 99.0 89.5 99.0 93.4 98.8 75.8 95.

1

88.9 98.7 84.0 98.0 A

M-i 16 d 1, 540 58 77.2 97.9 72.2 97.5 85.6 97.9 88.5 97.4 92.3 97.2 69.4 93.8 89.8 97.0 82.1 97.0 A

Average 73.3 98.4 74.6 98.0 85.4 98.8 83.8 98.7 87.8 98.4 72.0 95.6 85.0 98.4

BLUE, GROUND-COAT ENAMEL ON STEEL—NON-ACID-RESISTANT TYPE

N-l 4 c 1, 540-60 55 55.4 92.9 73.2 95.6 76.3 95.

1

74.8 97.5 77.0 94.4 70.6 95.6 69.9 94.9 71.0 95.2 C

N-2 9 c 1, 540-60 52 68.5 89.8 83.4 92.2 77.8 92.

1

83.4 94.8 78.4 92.2 68.2 90.7 70.0 86.0 75.7 91.1 D

N-3 1 d 1,540 55 66.0 97.8 67.7 98.4 81.9 98.8 80.7 99.1 85.3 99.2 67.6 96.2 75.3 94.9 75.0 97.8 C

N-4 18 d 1,540 55 66.6 96.8 72.4 98.4 82.0 99.0 82.

1

98.9 85.3 99.0 69.5 96.2 76.4 94.8 76.3 97.6 C

Average 64.1 94.3 74.2 96.2 79.5 96.2 80.2 97.6 81.5 96.2 69.0 94.7 72.9 92.6

GREEN MAT ENAMEL ON STEEL—CLEAR, ACID-RESISTANT FRIT MATTED WITH CALCINED ALUMINUM OXIDE

P-l 2 a 1,510 52 72.3 98.8 82.9 99.6 80.4 99.4 71.1 99.5 76.8 99.5 65.2 98.1 73.6 99.5 74.6 99.2 A

P-2 6 a 1,520 43 76.9 94.6 85.5 99.

1

82.2 99.1 71.6 99.1 72.2 99.0 70.4 95.0 73.9 99.0 76.1 97.8 B

P-4 7 d 1,480 35 90.9 92.9 96.0 98.1 96.5 99.6 89.9 99.2 86.1 98.8 82.5 97.9 53.8 95.7 85.1 97.5 C

Average 80.0 95.4 88.1 98.9 86.4 99.4 77.5 99.3 78.4 99.1 72.7 97.0 67.1 98.1

GREEN MAT ENAMEL ON STEEL—SEMI-OPAQUE, ACID-RESISTANT FRIT MATTED WITH CALCINED ALUMINUM OXIDE

PA-1 7 a 1, 480 30 40.3 96.3 62.2 96.6 85.2 98.8 85.4 99.1 74.

1

98.2 34.6 95.9 61.0 89.0 63.3 96.3 D

PA-2 3 a 1,480 40 47.1 96.5 69.7 97.3 82.6 98.3 96.1 99.1 81.4 98.2 64.2 97.9 58.2 95.

1

71.3 97.5 C

PA-3 2 d 1,480 17 91.6 99.4 92.3 99.1 95.0 98.6 90.8 98.4 87.8 98.4 92.0 98.8 89.2 98.2 91.2 98.7 C

PA-4 6 d 1,480 13 88.7 98.4 90.

1

98.1 92.6 97.9 87.6 98.0 82.2 98.0 95.8 97.9 91.8 98.1 89.8 98. 1 C

Average 66.9 97.6 78.6 97.8 88.8 98.4 90.0 98.6 81.4 98.2 71.6 97.6 75.0 95.1

See footnotes at end of table.

5
Table 3. Optical data and acid resistance spot test ratings of enamels—Continued

AverPercentage of initial gloss retained (Gr) and color retention (Cr) after exposure

for 3 yrs at —b—

Citric

Specimen

identification

Fabricator of speci- mensFrit supplier

U eport ed

firing temperature

age

initial specular

gloss »

Kure Beach—

80 ft

Kure Beach—

800 ft

New

Orleans Dallas LosAngeles

Pitts- burgh » Washington Average

acid

spottest rat- ing d Gr Cr Gr Cr Gr Cr Gr Cr Gr Cr Gr Cr Gr Cr Gr

GREEN MAT ENAMEL OX STEEL—CLE All, ACID-RESISTANT Fit IT MATTED WITH BARIUM METAPHOSPH ATE

R-l s a 1,430 18 52.3 97.0 68.8 96.4 74.2 96.4 72.0 95.8 64.3 97.0 76.0 97.9 59.2 97.4 66.7 116. S B

R-2 1(1 a 1,520 19 53.3 97.3 62.4 95.8 66.5 95.9 69.3 95.3 66.2 97.2 56.0 96.4 58.3 96.9 61.7 96.4 B

R-4 2 d 1,480 30 36.2 96.0 42.5 95.4 47.2 94.2 45.9 94.7 46.2 94.4 97.6 96.5 47. 4 95.

1

51.9 95.2 B

47.3 96.8 57.9 95.9 62.0 95.5 62.4 95.3 58.9 96.2 76.5 96.9 55.0 96.5

OREEN MAT ENAMEL ON STEEL—SEMI-OPAQUE, ACID-RESISTANT FRIT MATTED WITH BARIUM M ETAPHOSPIIAT

E

RA-1 2 a 1,480 31 61.2 93.8 74.3 94.0 82.2 95.9 78.9 95.4 42.1 95.5 92.0 97.3 84.0 95.1 73.5 95.3 B

RA-2 18 a 1,480 32 64.4 94.6 54.6 94.3 74.0 96.

1

74.5 95.0 40.8 96.5 69.5 96.7 70.5 94.2 64 n 95.3 B

BA-3 8 d 1,430 21 64.

1

97.4 76.6 96.3 85.4 97.1 87.3 95.9 69.6 97.4 80.8 96.0 86.7 90.

2

78.6 96.6 B

RA-4 6 d 1,480 7 62.1 95.8 53.4 95.4 63.2 94.7 62.7 95.8 67.5 95.9 60.1 89.5 62.6 95.0 61.6 94.6 B

Average.. 63.0 95.4 64.7 95.0 76.2 96.0 75.8 95.5 55.0 96.3 75.6 94.9 76.0 95.1

OREEN MAT ENAMEL ON STEEL—CLEAR, ACID-RESISTANT FRIT MATTED BY PROPRIETARY ADDITIVE

S-l 3 e 1,500 38 51.0 96.2 52.5 94.3 67.9 95.9 73.6 96.2 77.8 96.7 57.1 95.8 59.1 93.6 62.7 95.5 C

S-2 14 e 1,480 44 36.1 95.8 45.7 94.0 49.5 95.2 68.9 98.0 44.0 96.5 44.9 95.6 44.5 94.2 47.6 95.6 C

Average 43.6 96.0 49.1 94.2 58.7 95.6 71.2 97.

1

60 9 .96.6 51.0 95.7 51.8 93.9

GREEN MAT ENAMEL ON STEEL—SEMI-OPAQUE, ACID-RESISTANT FRIT MATTED WITH PROPRIETARY ADDITIVE

SA-1... SA-2

Average

4

9

ee

°F

1,520

1, 540

38

43

55.4 42.6

95.2

96.4 68.047.9

92.9

95.4 71.9

55.9

95.4

97. 1 79.8 64.2

95.8 97.969.8

67.4

96.

1

98.1

63.0 48.096.4 96.858.0 39.3

91.6

94.7 66.6

52.2

94.8 96.6 C

C

49.0 95.8 58.9 94.2 63.9 96.2 72.0 96.8 68.6 97.1 55.5 96.6 48.6 93.2

OREEN, GLOSSY 1,300° F ENAMEL ON STEEL

T-l T-2

Average

1119f

f

1, 330

1, 300

57

58

73.7 85.298.6

99.2 80.2

93.8

99.3

99.4

87.1 91.398.7 99.683.2

89.5

97.8 99.786.3

91.7

98.6 97.773.6

74.6

98.3 97.4

83.6

92.7

98.7

98.8

81.1 88.498.6

98.8 BAA

79.4 98.9 87.0 99.4 89.2 99.2 86.4 98.8 89.0 98.2 74.1 97.8 88.2 98.8

RED, GLOSSY 1,300° F ENAMEL ON STEEL

TJ-1- U-2._

1119

f

f 1,320

1, 300

52

53 62.478.7 89.593.5

86.8

84.8

92.8 95.593.6

89.8 94.795.9 89.0

87.8

94.9

95.8

95.6

96.

1

90.8

93.8

81.2

92.5 93.295.9

79.4

85.1 95.095.9 84.087.8

93.0 95.2 BB

70.6 91.5 85.8 94.2 91.7 95.3 88.4 95.4 95.8 92.3 86.8 94.6 82.2 95.4

YELLOW, GLOSSY ENAMEL ON ALUMINUM—ACID-RESISTANT TYPE

V-l 20 e 1.000 65 40.5 96.5 49.4 95.6 67.9 95.

1

79.6 96.8 77. 1 97.2 66.6 94.0 60.0 98 0 63.0 96.2 AA

V-2... 10 e 1.000 70 29.6 97.0 47.2 96. 7 69.3 96.2 78.3 96.7 77.6 96.8 55.9 92.0 62.8 98.5 60. 1 96.3 AA

V-3_ 20 g 1.000 83 25.8 81.7 71.2 85.8 79.2 95.5 78.8 96.5 81. 1 94.6 65.8 92.5 59.5 94.0 65.9 91.5 B

V-4.._ 10 g 1.000 85 18.9 85.8 69.7 89.7 78.4 96.4 81.4 97.9 81.8 96.1 66.0 88.3 53.6 96.0 64.3 92.9 A

Average 28.7 90.2 59.4 92.0 73.7 79.5 97.0 79.4 96.2 63.6 91.7 59.0 96.6

GREEN, GLOSSY ENAMEL ON ALUMINUM—ACID-RESISTANT TYPE

W-l___. 20 e 980 69 35.8 95.8 41.4 95.5 78.5 97.2 82.3 97.8 77.

5

97.1 65. t 96.4 55.5 95.5 62.4 96.5 A

W-2 10 e 1,000 77 39.8 98.6 68.

1

93.7 65.3 98.0 77.1 98.6 70. 5 97.6 63.6 96.5 59.8 99.0 63.5 97.4 AA

W-3 20 g 1,000 82 11.6 85.0 33.9 90.

1

76.9 96.9 80.2 99.0 73.9 98.7 70.0 98.5 67.9 95.6 59.2 94.8 A

W-4 10 g 1.000 81 21.5 87.7 41.

1

88.9 70.3 96.4 78.6 99.5 69.9 98.6 69.7 98.4 55.3 96.7 58.1 95.2 A

Average 27.2 91.8 46.

1

92.0 72.8 97.1 79.6 98.7 73.0 98.0 67.4 97.4 59.6 96.7

GREEN, MAT ENAMEL ON ALUMINUM X-l 20 e 990 13 93.6 98.6 86.

1

98.

1

81.7 97.0 80.8 97.7 68.2 97.6 67.5 96.3 68.8 96.8 78.1 97.5 AA

X-2 10 e 1. iiiiii 56 67.9 97.2 89.7 98.8 77.8 98.9 78.1 99.1 72.4 99.1 72.0 99.0 61.5 99.1 74.2 98.8 AA

X-3 _ 20 g 1.000 4 96.9 95.6 90.6 95.8 100.0 97. 5 83.7 97.7 62.3 96.0 85.

1

97.3 70.8 96.6 84.2 96.6 A

X-4 10 g 1,000 20 64.6 95.2 58.4 95.5 83.6 97.9 81.

1

98.0 65.3 98.2 67.7 97.7 52.4 97.9 67.6 97.2 A

Average 80.8 in, i, 81.2 97.0 85.8 97.8 80.9 98.1 67.0 97.7 73.1 97.6 63.4 97.6

See footnotes at end of table. 6
Table 3. Optical data and acid resistance spot test ratings of enamels—Continued

AverPercentage of initial gloss retained (Gb) and color retention (Cr) after exposure

for 3 yrs at —•>

Citric Specimen

identificat ion

Fabricator of speci- mensFrit sup- Reported

firing temperature

age

initial spec- ular

gloss »

Kure

Beach

80 ft

Kure

Beach

800 ft

Xew

Orleans Dallas Los

Angeles

Pitts- burgh c Washington Average

acid

spottest rat- ing d GB Cb Gb Cb Gb 1 Cb

1 Gb Cb Gb Cb Gb Cb Gb \ Cb Gb Cb

WHTEE, GLOSST EXAMEL OX ALUMINUM

VA-1 VA-2

Average.

20

10 aa

980

1.000 8181

14.7 67.2

96.5

95.6

S9. 7 95.9

103.* 95.7 82.176.9

95.2

96.7

77.6 97.5

78.9 98.5

77.4 77.8 95.9

96.5

64.3

59.0

95.

1

96.2

66.1

53.8

98.3 67.4

97.6 , 73.9 96.396.7 AAAA

41.0 96.0 96. 8! 95.8 79.5 96.0 7S.2 98.0

| 77.6 96.2 61.6 95.6 60.0 98. 0

OREEX, GLOSSY 1.000° F ENAMEL OX STEEL

P.ED, GLOSSY 1,000° F ENAMEL OX STEEL

Z-l. 21 e 1.000 47 36. 68.3 63.4 91.2 92.21 92.0 79.6 90.5 77.3 91.1 74.! 81.3 B

1 45° gloss measured in accordance with ASTM Designation: C346-55T (ref. o). b Computed from averages of three specimens at each site.

' Dirt films were present on some specimens after cleaning treatment.

d Ratings were made in accordance with Test for Acid Resistance of Enamels, Part I, Flatware (ref. [9]) except that grading of class A and class B enamels was modified to conform with Specification for Architectural Porcelain Enamel on Steel for Exterior use (ref. [10]).

of the 3-yr color retention, CR, which was arbitrarily defined as

:

Ca =100— AE.

The color difference. AE, was computed from

the measured values by use of a high-speed digital

computer [8]. The computer program was ar- ranged to give averages and standard deviations

as well as individual values for CR. The average 3-yr color retention for each enamel

at each site is listed in table 3.

6. Comparison of Exposure Sites

Table 4 gives the average values for percentage

gloss retained and color retention at each exposure

site. The averages are for all porcelain enamels

tested. The data listed in table 4 were treated statis- tically to determine the significance of the differ- ences (95 percent confidence level) between sites. Table 4. Average gloss and color retentions for all enamels

tested

Exposure site Site severity Gr» Cr*

Dallas Mill 80.2

80.6

79.9

70.

1

70.1 68.4

59.1

96.3

94.6

94.0 92.8

92.6

93.

1

91.7

Los Angeles Xew Orleans Pittsburgh _ . _

do.

do- Moderate.. ._ Kure Beach, 800 ft do Washington - . _ do Kure Beach. 80 ft . Severe

» Percentage of initial gloss retained.

b Color retention, Cr. = 100—AE where AE is color change in XBS units.

This analysis showed that the sites coidd be placed

into three groups: (1) mild—Dallas. Los Angeles,

and Xew Orleans; (2) moderate—Pittsburgh, Kure

Beach-800 ft, and Washington; (3) severe—Kure

Beach-80 ft. The clifferences between groups are highly significant.

The effect of exposure site on the different

enamel types is given in tables 5 and 6. In these

two tables the enamels of each type have been

further subdivided according to their citric acid

spot-test ratings. These ratings were assigned on

the basis of the Porcelain Enamel Institute Test

for the Acid Resistance of Porcelain Enamels [9], except that the rating of class A and class B enamels was modified to conform to a recent specification for architectural porcelain enamels on steel

[10].A close inspection of tables 5 and 6 shows that

for almost everv enamel tvpe, the exposure condit ions are less severe at Dallas, Los Angeles,

and New Orleans than at the other four sites. These differences in severity are especially noticeable in the case of the regular glossy steel enamels.

For these regular glossy steels, some of the nonacid-resistant types had equally as high percentage

gloss retained and color retention at the mild sites as the acid resistant types did at the other sites. A statistical analysis showed, for example, that

there was no significant difference (95 percent

confidence level) in either percentage gloss retained

or color retention between the average for class C enamels exposed at DaUas, Los Angeles, and

Xew Orleans and the average for class A A enamels exposed at Kure Beach-800 ft, Washington,

and Pittsburgh.

7
Table 5. Effect of mild, moderate, and severe sites on the percentage gloss retained of glossy enamels with different acid spot-test ratings

Krmmel type

Reg. steel (fired 1,430-1,580 °F).

1,300 °F steel

1,000 °F steel

Screening-paste

steel.

Aluminum

.

Exposure sites averaged

N.O., Pallas, L.A

KB-800, Wash.,

Pitts. KB-80

N.O., Dallas, L.A

KB-800, Wash.,

Pitts. KB-80

N.O., Dallas, L.A

KB-800, Wash.,

Pitts. KB-80

N.O., Dallas, L.A

KB-800, Wash.,

Pitts. KB-80

N.O., Dallas, L.A

KB-800, Wash.,

Pitts. KB-80

Exposure

repre- sented

Mild

Moderate.

Severe

.

Mild

Moderate.

Severe

Mild

Moderate.

Severe Mild

Moderate.

Severe

.

Mild

Moderate

Severe

.

Average percentage

gloss retained ( Or)

for enamels with

acid spot-test rating of— «

AA A B

8S. 2 79.0

87.8

sr,. 2

74.0

::; o

78.1

71. 1

52. 5

75. 5

62. 1

38.4

N5 7 70.3

71.7

81.fi 71.5

03. 4

77.5

57.5

21. 9

87.7 77.2

71.3

89, o 83.0

71.fi

86.4

73. 5

36. 7

81.0

70.7

8.8

79.7

65. 5

25. S

81.0 65.3

55. 2

76.4

59.0

25. S

76. 1 54.2

• Citric acid spot-test ratings were made in accordance with Test fnr Acid

Resistance of Enamels, part I, Flatware (Ref. g) evcept that the grading of

class A and class B enamels was modified to conform with Specification for Architectural Porcelain Enamel on Steel for Exterior Use (Ref. 10).

Table 6. Effect of mild, moderate, and severe sites on. the color retention of colored enamels with different acid spottest ratings

Enamel type

Reg.steel(glossv)

(fired 1, 430-

1,580 °F.)

Reg. steel (mat)

(fired 1, 430-

1,540 °F.)

1,300 °F steel (glossy).

1,000 °F steel (glossy).

Screening-paste

steel (glossy).

Aluminum (glos- sy).

Aluminum (mat)

Exposure sites averaged

N.O., Dallas, L.A

KB-800, Wash.,

Pitts. KB-80

N.O., Dallas, L.A

KB-800, Wash.,

Pitts. KB-80

N.O., Dallas. L.A

KB-800, Wash.,

Pitts. KB-80

N.O., Dallas, L.A

KB-800, Wash.,

Pitts. KB-80.

N.O. Dallas, L.A. KB-800, Wash.,

Pitts. KB-80

N.O., Dallas, L.A

KB-800, Wash.,

Pitts. KB-80

N.O., Dallas, L.A

KB-800, Wash.,

Pitts. KB-80

Exposure

represented

Mild

Moderate

Severe. .

.

Mild

Moderate.

Severe. Mild

Moderate.

Severe.. Mild

Moderate

.

Severe... Mild

Moderate

Severe. Mild.

Moderate.

Severe Mild

Moderate

Severe.

Average color retention (C R) for enamels

with acid spot-test rat- ing of—" AA A B C D

98. 9 98.1

97.6

98. 6 97.6

99. 5

99.

1

99. (I 98.5

99.2

92.0

92.0

93.9

90.4 88.5

84.9

97.0

96.0

97.4

98.0

98.3

97.9

\5. li

82. 5

97.6

94 I

97. 6

96.

8

95. 4

96. 3 95.9

95.

95. 7 96 I

90. 9

55.4

74. 9 61.9

55. 9

95. 5

llll K

81.7

98. 0

97.7

96.4

73.9

71.2

60.1

95.2

98.7

93.8

» Citric acid spot test ratings were made in accordance with Test for Acid

Resistance of Enamels, part I, Flatware, (ref. [9]) except that the grading

of class A and class B enamels was modified to conform with Specification

for Architectural Porcelain Enamel on Steel for Exterior Use (ref. [10]).

The differences in severity of the sites cannot be

explained by the differences in weather conditions

(see table 2). New Orleans, for example, has the

highest annual rainfall and the highest average

temperature of any of the seven sites, yet the New

Orleans exposure is one of the three mildest. This

suggests that some other factor is affecting site severity.

Table 7 was prepared from unpublished data of the National Air Sampling Network of the U.S.

Department of Health, Education, and Welfare.

The methods used for collecting and analysing the

samples is given in a report issued in 1958 [11]. No information was available as to the content of

acid gases in the respective atmospheres. However, because these gases tend to react with other

substances in the air to give acid salts, the composition of the particulate matter (columns 4 and

5 in table 7) is believed to give a good indication

of the acid contents of the various atmospheres

[11].Table 7 shows that the New Orleans site has a

relatively low level of air pollution. It has the

lowest particulate and N03 contents, next to the

lowest S04 content, and next to the highest pH.

At the same time, Los Angeles, which is one of the

mildest sites, has high ah pollution (see table 7).

However, the average annual rainfall in Los Angeles is only 12.1 in. It seems reasonable to assume

that it is lack of moisture that accounts for the mild

conditions at Los Angeles.

ble 7. Averages of air pollution measurements made

'wring 1.958 by the National Air Sampling Network of the J.S. Department of Health, Education, and Welfare

Table 7.

(II

City

Total suspend- ed particulates

Composition of particulates

Organic

matter S04 N03 Other pH *>

214 30.4 16.1 9.5 158.0 6.0 Pittsburgh 167 13.0 15.2 2.7 136.

1

6.4 Washington, D.C 111 12.9 12.4 3.1 82.6 6.7 Xew Orleans 92 11.4 9.5 2.2 68.9 7.0 Dallas 113 10.2 7.1 2.3 93.4 7.1

a Micrograms per cubic meter of air. Values are averages of measure- ments taken at approximately biweekly intervals.

b Measured for solutions prepared by refluxing an 8 percent aliquot of particulates with 50 ml of distilled water and diluting to 80 ml. Values are averages of measurements made at approximately biweekly intervals.

Figure 3 shows two curves in which the pH of

the atmospheric particulates has been plotted

against the average 3-yr color retention for those

sites which have rainfalls of 34 in. or greater and

for which pH data were available (Pittsburgh,

Washington, New Orleans, and Dallas).4 The

lower curve is for all enamels included in the test while the upper curve is for the class A and class AA regular glossy steel enamels. Both curves

suggest that acidic substances in the atmosphere

are affecting the site severity of these particular

urban sites. The curve for the regular glossy

steel architectural enamels (class A and class AA

see reference [10]) is of special interest in that[it

' The same general type of curves are obtained if the combined X*03 and

SOt contents in table 7 are plotted against color retention.

S
CLASS AA AND A

6.4 6.6 6.8 7.0 7.2 AVERAGE pH FROM AIR POLLUTION SURVEY Figure 3. Change in 3-yr color retention of enamels with pH for the urban exposure sites with annual rainfalls of 34

in. or greater. Measurements of pH were made during 1958 by the National Air Sampling Network. Letters adjacent to points indicate exposure city; P

Pittsburgh, W—Washington, NO—New Orleans, and D—Dallas.

shows that appreciable color change for enamels

of this type occurs only when the pH of atmospheric particulates falls below 7.0. The lower

curve fall enamel types) reflects the presence of

enamels of class B, C, and D acid resistance in the

averages. Some enamels with these ratings showed appreciable changes in gloss and color even at the mild sites. Also, the magnitude of the changes

for enamels of poor resistance appeared to be less dependent on the pH of the air cont aminants than on the average annual rainfall. This is evident

by a comparison of the data in table 3 for Dallas

and ]Sew Orleans with the acidities of air con- taminants in table 7 and rainfalls in table 2. Although the pH of sea water is approximately

8, the Kure Beach-80 ft site is, on the average,

the most severe of the seven (see table 4). The

nearest population center is some 20 miles distant

from Kure Beach and almost no air pollution

from fuel combustion would be expected. Salts

from the ocean are present in abundance, however, and it is probably these salts combined

with the almost continuous presence of moisture

that creates the severe environment. The conditions 800 ft from the beach are less severe than

those at 80 ft. Tables 5 and 6 show that the sea spray conditions at the Kure Beach-80 ft site are especially

severe on the aluminum enamels, the screeningpaste steel enamels, and the class B 1,000 °F steel enamels and it is mostly because of this severity

that the averages given in table 4 for the Kure

Beach-80 ft specimens are so low. Aluminum

enamels and the 1,000 °F steel enamels contain

high proportions of lead oxide and the screeningpaste steel enamels may contain some lead. It

is possible that the chloride in the sea spray reacts with the lead in the enamel surface to form soluble

lead chloride. Thus, it would seem from the

3-yr results that a porcelain enamel high in lead

oxide should not be used in a sea-spray environment unless exposure data should first indicate

its suitability. That some high-lead enamels do

have fairly good resistance at the Kure Beach80 ft site is evident from the mat enamels X-l

and X-2 in table 3.

7. Comparison of Enamel Types

Table 8 gives the average color retention and

percentage gloss retained at all sites for each

enamel type. The type with the best color

stability is listed at the top ; the type with the

poorest, at the bottom. The percentage gloss

retained for the mat enamels is not included

inasmuch as this measurement has little meaning

because of the low initial gloss values of the mat

finishes. Table 8. Average color retention (Cr) and percentage gloss retained (Gr) for the eight types of enamels

Averages for all sites

Enamel type a Avg. for all enamels

Best enamel of type

Cr Gr Cr Or

A. Reg. gloss v steel—AR ... B. Mat aluminum—AR98.2

97.5

96.4

96.4

96.5

95.1 86.8

81.8

81.2 99.0

98.8 98.8

99.2

98.7

97.4 93.7

92.9

88.8

C. 1,300 °F steel—AR

D. Mat steel—AR

85.3 88.4

E. Reg. glossy steel—Non-AR

F. Glossv aluminum—AR

G. 1,000 °F steel—AR

H. Red and yellow screening steel—AR.

67.8

63.8

75.6

74.0

76.3 65.9 77.2

81.9

a Enamels with citric acid spot test ratings of AA, A, or B are designated

as AR (acid-resistant); those with C and D ratings are designated Non-AR

(non-acid-resistant)

.

The averages given in the first two columns in

table 8 are for all enamels of each type that were

included in the test. 5 The last two columns list the CR and GR values for the particular enamel

with the best weather resistance of each type

tested. Even on this "best-of-class" basis, the

regular gloss}- acid-resistant steel enamels appear

to have the best resistance of the eight types

while the glossy aluminum, 1,000 °F steel, and

screening-steel enamels have the poorest. An

analysis of the enamels opacified with titanium

dioxide shows that this type is equally as resistant

as the other types of regular steel enamels.

5 Application of Fisher's "I" test to the data given in the first two columns

of table 8 showed that there is a sinaifieant difference (95 percent confidence

level) between all listed averages with the exception of C-D, C-E, and D-E

for gloss and H-G for color.

9
While the mat steel enamels, as a group, arc

not especially resistant to color change (first column, table 8), the compositions with class AA

spot-tost ratings show quite high color retentions.

Enamels PA -3 and PA 4, in particular, have

color retentions alter 3 yr that are comparable to

i he best oi t he glossy enamels (table 3) . All of the

mat enamels Included in the earlier test [2] were

exceptionally poor with respect to color stability.

It follows that some of the mat enamels that have

been produced since World War II are much more

stable. The mat aluminum enamels, as a group, show

the second best color retention of all of the enamel

types (table 8), and some of the glossy aluminum

enamels showed good stability at some sites. A

recent paper by Sopp, Wallace, and Picker [12] gives the color change of three glossy green

aluminum enamels after about 3 yr on a roof at New Kensington, Pa. The measured color change

for a class A enamel was 4.0 NBS units. This

value is in fair agreement with the color change

reported in table 3 for three class A green glossy

aluminum enamels exposed at Pittsburgh, where

similar exposure conditions might be expected

(average AE—-2.2 NBS units). The average

change for the same three enamels exposed at Kure Beach, SO ft, however, was 10.5 NBS units

while at KB-800 ft it was 8.5 units.

8. Effect of Exposure Angle

A comparison of the color retention and percentage gloss retained of the 45 enamels that were

exposed (a) vertically facing south and (b) at a 45° angle facing south at the Washington site suggested that the difference in the degree of

attack was related to the weather resistance of the

enamel. As a check on this possible relationship,

the enamels were placed into five groups based on

an arbitrary weather resistance rating of the

enamels when exposed at 45°. The following

summarizes the rating system :

Weather resistance rating

Limits of percentage

gloss retained,

Gr

Limits of color

retention, Cr

1 80 to 100

65 to 80

50 to 65

35 to 50

0 to 35

97. 5 to 100

95. 0 to 97. 5

92. 5 to 95. 0

90. 0 to 92. 5 0 to 90. 0

2

34

5

For an enamel to receive a No. 1 rating it would

need to have both an average GR between 80 and

100 and an average CR between 97.5 and 100;

however, if the values for either GR or CR fell outside these limits, the enamel would be given

the lowest applicable rating. Thus, an enamel

with a GR of 89.0 and a 0B of 91.3 would be given

a No. 4 rating.

Table 9. Comparison of percentage gloss retained, Cr,

and color retention, Cr, for representative glossy enamels

exposed on vertical and 45° racks at Washington, D.C. site

Weather resistance rating on 45° Rack "

No. of enamels

averaged

Average Or Average C r

i>

Vertical Vertical 45°

1 6 82.9 85.7 99.2 98.9

2 15 74.4 78.0 98.0 97.6

3 12 fiG. 5 <S0. 5 97.2 96. 0

4 4 54.3 42.1 95.1 93.5

5... 8 63.2 59.3 88.4 79.7

a See text for method used for assigning ratings.

'» White enamels not included in averages. The results (table 9) show that the enamels

with No. 1 and No. 2 ratings lose slightly more

gloss (lower GR values) when exposed vertically

than when exposed at 45°. Those with No. 3, 4. and 5 ratings, however, lose more gloss when

exposed at 45°. The loss in color (lower CR) was

always greater when the enamels were exposed at 45° than when they were exposed vertically.

Another observation of interest is that as the weal her resistance rating decreases, and the differ- ence in color retention values between the 45°

and vertical exposure tends to increase. This is brought out by figure 4.

96

O

cn 88

8 )

76

1 1

VERTICAL RACK

\^ \

\ \

\ \

\ \ \ \

\ \ /\ b _ 45° RACK \

i i I 0 12 3 4 5 WEATHER RESISTANCE RATING ON 45°RACK

Figure 4. Effect of exposure angle on the color retentions

of enamels exposed at Washington, D.C.

Method used for assigning weather resistance ratings is given in text. The only conclusion on exposure angle that seems safe to draw at 3 yr is that exposing the

specimens at 45° rather than vertically accelerates

the weathering action of those enamels with poor

weather resistance. The increased attack, while

significant, is not so large that an enamel that was considered to have poor weather resistance

(No. 4 and 5 ratings in table 9) when exposed at 45° would not also be considered to have rather

poor resistance when exposed vertically.

10
9. Correlation of Weather Resistance

with Citric Acid Spot Test

A number of earlier investigations of weather

resistance of porcelain enamels have shown that a

direct relationship exists between acid resistance

and weather resistance [2, 12, 13, 14]. As can be

seen from tables 5 and 6, this same general type

of relationship was noted in the present investigation. However, as in the 15-yr stud}' [2], the

correlation exists only when averages are considered and there are many individual exceptions

to the pattern.

Figure 5, which is a plot of the individual values

for the regular glossy steel enamels at Washington,

is typical of the color retention results. The

dashed line drawn through the average for each

acid resistance class shows that a correlation exists between the citric acid spot-test rating and the

weather resistance as measured by color retention.

Although the points show a high scatter, it will be

noted that all class AA and class A enamels have

color retentions of 97.0 or above, which might be

considered as reasonably good color stability after 3 yr of exposure. However, there is one

class C (E-l in table 3) and one class D enamel

(E-4 in table 3) that show equally as good color

retention as any of the class AA or class A enamels.

The percentage gloss retained for these two

enamels at Washington is also high (71.7 and 74.2,

respectively). Thus, on the basis of short -time

tests only, these two enamels might be considered

as suitable for architectural use even though they

fail the citric acid spot-test requirement of the

architectural specification [10].

98

86

1

I ' T i

0 O o o 00

O OOo°

• 5»x>

o o

"-

~~ ^ o

o ^

•

\

\

\

\

\

\

•

o

0 INDIVIDUAL ENAMELS

• AVERAGE VALUES

I i i

o

AA A B C D CITRIC ACID SPOT TEST RATING Figure 5. Color retentions at Washington, D.C. for enamels

with different citric acid spot test ratings.

A shortcoming of the citric acid spot test is that it fails to predict the relatively poor color

stability of the 1,000 °F steel, the screening-paste

steel, and some of the glossy aluminum enamels

(see table 6). Obviously a test that gives a better

prediction of weather resistance than does the

citric acid spot test is needed and one of the longrange goals of the study is to develop such a test. 10. Copper Sulfate Test for Predicting

Color Stability of Red and Yellow

Enamels

Many of the red and yellow enamels with high

citric acid spot-test ratings lacked good color

stability (table 3). The red and yellow screeningpaste enamels, for example, had the lowest color

retentions of any of the enamels tested. During

laboratory examination of these particular

enamels, it was discovered that the least stable

compositions would change in color when spot

tested with a saturated solution of cupric sulfate

for one hr at room temperature. Because of the

potential value of such a treatment for predicting

color stability of red, yellow, and orange enamels,

subsequent work was carried forward in which a number of possible variables in the testing were

investigated. This work led eventually to the

following test procedure

:

A saturated solution, prepared by adding 50 g

of cupric sulfate (CuS04

• 5H2 0) to 100 ml of water, was aUowed to stand for 16 hr at room temperature. A few drops were withdrawn from the upper

part of this solution and placed on the cleaned

enamel surface to form a small pool which was

covered immediately with a l-in.-diam watch glass.

The specimen with the watch glass in position was then placed under a plywood box painted

white on the inside. The inside dimensions of the

box were 20x6x12 in. A 15 w "white" fluores- cent lamp, 1 in. diam x 18 in. long, was centered

3 in. from the top of the box so that its center line was 9 in. from the specimen. With this arrangement, the light intensity at the specimen surface was 300 foot candles. 6 After 20 hr at room temperature, the specimen was removed, the copper sulfate solution rinsed

away with water, and the treated area examined

for evidence of a visual change in chromaticity.

If a change could be detected by visual examination, the enamel failed the test; otherwise it passed.

Table 10 compares the results obtained with

this test for all class A and class AA red and yellow

porcelain enamels included in the test with their

average 3-yr color retention values. All enamels

of this type that pass the cupric sulfate test have

color retentions of 98.2 or above; all enamels that

fail have color retentions of 92.9 or below. Thus,

the test appears to be effective in separating those

class AA and class A red and yellow enamels of good color stability on weathering from those of

6 Experiments showed that the reaction between the cupric sulfate solution and the enamel surface was partly photochemical in nature and that a controlled light source was essential to obtain a suitable separation of enamels.

11
Table 10. Cupric sulfate test ratings and average 8-yr color retentions of red and yellow enamels with class A and class AA citric spot test ratings

Average Enamel Enamel type Enamel CuSChtest color designation color rating retention

Ir-2 Beg. glossy steel Yellow Pass 98.4 L-3 ...do ...do 98.3 L-4 ...do ...do 98.2 L-l do ...do ...do '.IS. > D-4 do Red ...do 98.

3

Q-l Screening-paste steel Yellow.... Fail 92.8 G-2 do do do 88. 8

U-3~_~.~.~_~_~.~-~.~.~. '''.(lo'."".'.'.'. '.'.'.do""'." 92! 9 G-4 ...do ...do 92.5 GA-1 """do""~~"~"""II"." ...do. ...do 80.4 GA-2... lo ...do ...do. 81.9 GA-3 ...do ...do 83.

4

OS-4 ...do ...do 82.8 F-2 do i? Red ...do 84.2

poor stability. 7 Although the tost also separates

red and yellow enamels with citric acid spot-test

ratings of class B and lower, such enamels would

have already heen eliminated for architectural use (10) because of their hick of acid resistance.

11. Discussion

An analysis of the 3-yr data suggests that the

factors responsible for changes in surface appear- ance of enamels with weathering are:

(1) Moisture.

(2) Atomospheric pollution by acidic substances.

(3) Sea spray and sea air at ocean sites. Although sea air can cause rapid weathering of some enamel types, neither moisture nor atmospheric pollution by acidic gases, of itself, appears

to cause a rapid change in enamels. However,

moisture in combination with air pollution apparently can produce a fairly fast weathering ac- tion of some types of porcelain enamel.

The relatively large effect of exposure location on the measured changes in gloss and color was

not observed in the 15-yr investigation [2]. In

this earlier study, however, there were no sites comparable to New Orleans, Dallas, and Los Angeles. The comparatively mild conditions that

exist at these sites suggest that either (a) a less resistant enamel can be used to achieve equally as good color and gloss retention as at the more

severe sites, or (b) the same enamel will show less change in surface appearance in any given time

period. However, because there is usually a lack

of exact knowledge as to severity of conditions at a proposed building site, and also because the

producer does not always know where his product

will be used, the safest approach might be to consider as architectural enamels only those compositions that give the best resistance to all types

of weather conditions.

' Although table 10 implies that all screening-pasto steel enamels will fail the copper sulfate test and all regular steel enamels will pass extensive testing

of production enamels lias shown that there are some yellow and orange

regular steel enamels of good acid resistance that will consistently fail the

test; also, one architectural enamel producer has demonstrated that it is possible to prepare red and yellow screening-paste enamels that will consist- ently pass the test.

Most installations of porcelain-enameled metal

arc intended to maintain good appearance for 20

yr or longer. It cannot be stated with certainty

that those enamels that show good resistance to weathering at 3 yr will also be good at 20. However, from the results of the 15-yr study [2], it seems probable thai (here will be very few deviations from the observed pattern with continued

testing.

The most recent specification for architectural

enamels on steel [10] requires that the enamel pass

a cil ric acid spot test that is described in the specification. Any enamel that passes this test will have a citric spot-test rating of either class A or

class AA by the system of grading used in the

present investigation. Practically all of the steel enamels with these ratings, and which also pass

the cupric sulphate test for red, yellow, and orange

enamels, as required by the specification, had good

weather resistance at the 3-yr inspection. The

only exception was enamel Y-l, which is a green

class AA enamel fired at very low temperature

(1,020 °F). This enamel, which showed a color

change of more than 10.0 NBS units at some sites in only 3 yr, does not have sufficiently good color

stability to be considered for architectural use. Obviously, a new test is needed that will predict

the poor color stability of enamels of this type. In addition, the new test should be capable of

predicting the rather large color changes that

occurred with the class A and class AA glossy

aluminum enamels at some of the more severe ex- posure sites.

12. Summary

An examination of 2,160 porcelain enameled

specimens of 28 types was made after exposure

for 3 years at Dallas, Tex. ; Los Angeles, Calif.; New Orleans, La.; Pittsburgh, Pa.; Washington,

D.C.; and two sites at Kure Beach, N.C. A sum- mary of the findings follows:

(1) Enamels exposed at all test sites except

Pittsburgh could be cleaned reasonably well by

washing with a detergent.

(2) With one exception all enamels protected

the metal base from corrosion. The exception

pertained to specimens to which an unusual type

of low-fired steel enamel had been applied. At

the Kure Beach sites, these specimens showed rust

stains on the face surface. These stained areas were adjacent to pinholes in the enamel coating.

(3) For enamels of one type, a direct relationship was observed between the citric acid spot-test

rating and the weather resistance as measured by

changes in gloss and color. This relationship,

however, existed only when averages were considered. Also, relatively large variations in weather resistance were observed between different

types of enamel with the same spot-test rating.

(4) The exposure conditions were found to be

least severe, on the average, at Dallas, Los Angeles,

and New Orleans; of intermediate severity at Pittsburgh, Kure Beach-800 ft, and Washington;

12
and most severe at Kure Beaeh-SO ft. The low

average resistance at Kure Beach-80 ft was caused,

for the most part, by the low resistance of certain

types of enamels to the sea spray environment.

(5) Comparison of gloss and color changes with

data from the National Air Sampling Network

indicated that air pollution by acidic contaminants

is an impgrtant factor at those urban sites that

have annual rainfalls of 34 in. or greater.

(6) On the average, the regular gloss}7" steel porcelain enamels showed the best weather resist- ance of any of the types tested.

(7) Class AA steel porcelain enamels fired at 1,300 °F showed a comparable weather resistance

to the Class AA steel enamels fired in the range

1,450-1,550 °F. Class AA steel enamels fired at 1,000 °F, however, showed relatively poor resist- ance at all sites. (8) The class A mat steel porcelain enamels

included in the test displayed a color stability that was comparable to the class A glossy steel enamels.

(9) The gloss}* aluminum porcelain enamels, as

a group, were not as resistant as the regular glossy- steel or the 1,300 °F steel enamels but they were somewhat more resistant than the 1,000 °F steel enamels. The class AA mat aluminum enamels, on the other hand, had a color stability that was

comparable to the class AA regular glossy steel enamels.

(10) All red and yellow screening-paste porcelain

enamels in the test showed relatively low color

retentions at all sites. It was found, however, that

this poor color stability could be predicted by a

specially developed cupric sulfate spot test. (11) Specimens with enamels of poor weather

resistance that were exposed vertically at Washington, D.C., showed significantly smaller changes

in gloss and color than similar specimens that were

exposed at 45°. Enamels with good weather

resistance, on the other hand, showed only minor

differences in the degree of attack with exposure

angle.

The authors gratefully acknowledge the help and

assistance of James H. Giles, Research Associate

of the Porcelain Enamel Institute from 1953 to 1956, who supervised the installation of the speci- mens at the exposure sites and who also supervised

the initial gloss and color measurements, and of Gerald Galler, Robert Hollis, and Donald

Hardesty, who made most of the gloss and color

difference measurements.' The authors are also indebted to the various frit manufacturers who

supplied the enamels as well as to the various fabri- cators who applied the enamels to the test specimens.

13. References

[1] Proceedings of Conference on Porcelain Enamel in the Building Industry, Research Conf. Report No.

6 of Building Research and Advisory Board,

National Academy of Sciences (National Research

Council, 2101 Constitution Ave., Washington 25, D.C., March 1954).

[2] D. G. Moore and W. N. Harrison, Fifteen-year ex- posure test of porcelain enamels, National Bureau

of Standards Building Materials and Structures Report 148, June 1957. For sale by Supt. of Documents, U.S. Govt. Printing Office, Washington

25, D.C. Price 15 cents.

[3] Alan Potter, First-year data on the weather resistance

of screening-paste enamels, Proceedings of the

Porcelain Enamel Institute Forum 19, 131 (1957). Porcelain Enamel Institute, Inc., 1145 Nineteenth

St., N.W., Washington 6, D.C.

[4] I. Nimeroff, H. K. Hammon, J. C. Richmond, and

J. R. Crandall, Specular gloss measurements of ceramic materials, J. Am. Ceram. Soc. 39, 103

(1956).

[5] Tentative method for 45-deg-specular gloss of ceramic

materials, ASTM designation: C346-55T, 1958

Book of ASTM Standards, Pt 5, p. 520. Am. Soc.

for Testing Materials, 1916 Race St., Philadelphia

3, Pa.

[6] R. S. Hunter, Photoelectric Color-Difference Meter,

J. Opt. Soc. Am. 38, 661 (1948).

[7] R. S. Hunter, Photoelectric tristimulus colorimetry

with three filters, NBS Circ. 429 (1942).

[8] Alan Potter, Using an electronic computer to reduce weathering data, Proceedings of the Porcelain Enamel Institute Forum 20, 73 (1958). Porcelain Enam. Inst., Inc., 1145 Nineteenth St., N.W.,

Washington 6, D.C.

[9] Test for acid resistance of porcelain enamels, Pt 1, Flatware. Issued by the Porcelain Enamel Insti- tute, Inc., 1145 Nineteenth St., N.W., Washington

6, D.C.

[10] Specification for architectural porcelain enamel on

steel for exterior use, PEI: S-100 (1959). Issued by the Porcelain Enamel Institute, Inc., 1145 Nineteenth St., N.W., Washington 6, D.C.

[11] Air pollution measurements of the National Air Sampling Network, Public Health Service Publ. No.

637, 1958. For sale by Supt. of Documents, U.S. Govt. Printing Office, Washington 25, D.C. Price

$2.00.

[12] A. L. Sopp, P. F. Wallace, and R. W. Ricker, Chemical and weather resistance of porcelain enamels on aluminum, Ceramic Age 75, 66 (1960).

[13] B. J. Sweo, Correlation of weather resistance of porcelain enamels with chemical test data, J. Am.

Ceram. Soc. 32, 333 (1949).

[14] R. Marker, Principles for testing weather resistance

of enamels, Silikattech 4, 343 (1953).

13

U.S. GOVERNMENT PRINTING OFFICE : 1362

U.S. DEPARTMENT OF COMMERCE

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NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

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