AlllDD TTE72fl

NAT'L INST OF STANDARDS & TECH RI C.

A1 11 00992728

Baker, Margaret A/Weather resistance of TA435 .U58 V50:1974 C.I NBS-PUB-C

c NBS BUILDING SCIENCE SERIES 50

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M

Weather

of Porcelain

Year Inspection o mi

1956 Exposure T
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Waltenaf Bureau of Starrfarch OV 1 1974

Weather Resistance of Porcelain Enamels-

^^^^^ 15-Year Inspection of the 1956 Exposure Test

Margaret A. Baker

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

50

Sponsored by the Porcelain Enamel Institute 1900 L Street, N.W.

Washington, D.C. 20036

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued July 1974
Library of Congress Catalog Card Number: 74-6000 34

National Bureau of Standards Building Science Series 50

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 50, 15 pages (July 1974)

CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

(Order by SD Catalog No. €13.29/2:50). Price 55 cents. Stock Number 0303-01282
Contents

Page

1. Introduction 1

2. Description of enamels and specimens 1

3. Exposure sites 6

4. Results and discussion 7

4.1. Cleaning of specimens 7

4.2. Corrosion of base metal 7

4.3. Measurements of gloss and color after 15 years 7

4.4. Effect of exposure time on changes in gloss and color 7

4.5. Comparison of exposure sites 9

4.6. Comparison of enamel types 10

4.7. Correlation of weather resistance with acid resistance 10

4.8. Cupric sulfate test for predicting the color retention of red and yellow enamels 11

4.9. Effect of exposure angle 11

4.10. Comparison with late 1930's enamels 11

5. Summary 12

6. References 12

iii

The Weather Resistance of Porcelain Enamels —

15-Year Inspection of the 1956 Exposure Test

Margaret A. Baker*

In 1956, an exposure test of porcelain enamels at 4 urban and 2 ocean shore sites in the conti- nental United States was initiated by the National Bureau of Standards and the Porcelain Enamel

Institute. After fifteen years, all exposed specimens were returned to the Bureau and the changes in gloss and color determined. The gloss changes were found to be significantly different at all exposure

sites except Pittsburgh, Los Angeles and Dcdlas. The most severe changes occurred at the Kure Beach, North Carolina, site nearest the ocean, while the least changes occurred at Pittsburgh, Los Angeles and Dallas. The differences in behavior of the specimens correlated with both the average relative humidity and the pH of the suspended particulate matter at the different sites. A correlation appeared to exist between the acid resistance of the enamels and changes in gloss and color. The regular, glossy, acid-resistant enamels on steel showed the best weather resistance of the various types tested. Comparison with enamel specimens exposed for fifteen years in an earlier test showed that porcelain enamels produced in the early 1950's were equally resistant to changes in gloss and color as those produced in the late 1930's.

Key words: Acid resistance; color; gloss; pH; porcelain enamel; relative humidity; weather resistance.

1. Introduction

The weather resistance of any building material

used in exterior applications is important to build- ing designers and to those responsible for mainte- nance. As early as 1939, the Enameled Metals

Section of the National Bureau of Standards and

the Porcelain Enamel Institute recognized the need

for accelerated laboratory tests for porcelain

enamels that would correlate with weathering data. The study of the weatherability of porcelain enamels

on steel begun in 1939 has resulted in a series of reports issued after exposure periods of 1 [1],' 7 [2], 15 [3], and 30 [4J years. The principal finding of this study was that the best enamels showed no ob- jectionable changes in gloss or color after 30 years'

exposure at Washington, D.C. and the enamels

with poor weather resistance could be determined

by relatively simple laboratory tests. In the early 1950's, several new enamel types

including low-temperature enamels for steel and

aluminum, and titania-opacified enamels, were

developed. It was important to determine whether

these new enamel types followed the same general

pattern with respect to weathering as those tested

earlier. Therefore, a new exposure test was initiated

in 1956. Progress reports of this test have been

published after 1 [5], 3 [6], and 7 [7] years' exposure.

The present paper is a progress report after 15

years' exposure. For ease of comparison, the same

general format is followed as was used in the 3

*Research Associate from the Porcelain Enamel Institute at the National Bureau of Standards, Washington, D.C, 1964 to 1973.

' Figures in brackets refer to literature references at the end

of this paper.

^ Frit is the principal ingredient used in preparing procelain

year report. Also, as an aid to the reader, the de- scription of the specimens and exposure sites is repeated in this paper. The next inspection of these enamels is tentatively planned after 30 years' exposure.

2. Description of Enamels and

Specimens

The 28 types of enamel included in this test were

furnished to 21 producers of architectural enamel

parts by seven companies who manufacture enamel

frits. The producers then applied the enamels to the test specimens. Table 1 includes coded identi- fication of the frit suppliers and fabricators, and

also lists the types of enamels. Minor variations in composition of the frit ^ for enamels of the same type

as supplied by the different manufacturers probably occurred. Likewise, different producers applying the same enamel may not have achieved an

identical finish, because of minor variations in miUing and firing. If these variations are taken into consideration, there were, in effect, 94 enamels

under study; of these 80 were applied to sheet steel and 14 to sheet aluminum. After 3 years' exposure,

three of the screening paste enamels ^ had become

so badly weathered that they were withdrawn from

further testing. The 91 remaining enamels are evaluated in this report.

enamel. It is formed by melting suitable glass-forming raw materials and then quenching the molten mass, usually in water.

^ Screening paste enamels are usually strongly colored enamels

of a consistency which permits their application to a previously

fired enamel surface by the silk screen process.

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The 4V2-inch-square specimens with flanged

edges were made from 18 gage sheet metal. A small

hanging hole was punched in one corner of each

specimen. Each enamel was applied to about 60

specimens; of these 21 were used for exposure test- ing (3 at each site), 2 were used as reference panels,

and the remainder were kept in dry storage to be

used in the development of accelerated weathering tests.

3. Exposure Sites

The six exposure-test locations and the general

exposure conditions for each site are given in table 2. The sites were selected to represent a range of ex- posure conditions found in the United States. The

racks at four sites were located on rooftops in industrial city areas of Los Angeles, California;

Dallas, Texas; Washington, D.C.; and Pittsburgh,

Pennsylvania. The remaining two sites were ground

sites at the International Nickel Company's Corrosion Laboratory at Kure Beach, North Carolina —

one at 80 feet from the ocean and the other at 800

Table 2. Exposure test locations

City Exposure site Exposed conditions represented

Kure Beach, N.C Ground, 80 ft. from Temperate, sea

ocean. spray. Kure Beach. N.C Ground, 800 ft. from Temperate, sea

ocean. air. Washington, D.C Roof. Industrial Temperate, comBuilding, National mercial. Bureau of Standards.

Pittsburgh, Pa Roof, U.S. Post Temperate, comOffice. mercial.

Dallas, Texas Roof, U.S. Post Texas, commercial.

Office. Los Angeles, Calif ... Roof, U.S. Post Southern CaliforOffice. nia, commercial.

Figure 1. Exposure rack showing the supporting struts, and

ceramic insulators used to position 3 of the 150 specimens the rack will hold when it is filled.

feet. Table 3 summarizes the average weather and

air quality data for each of the six sites as obtained

from the National Oceanic and Atmospheric Administration and the National Air Sampling Network.

There are no data in this report on the specimens

exposed at New Orleans because they were removed

from the roof of the Post Office Building prior to a hurricane after 8 years' exposure and were not

reinstalled. The specimens were loosely mounted in ceramic

insulators which were fastened to the metal

stretchers of supporting racks. The supporting racks were constructed of aluminum alloy, except those at the two Kure Beach locations which were made of

Monel metal. All specimens were exposed at 45°

degrees, enameled face up, and faced south except

at the Kure Beach-80 ft station where they faced the ocean at east-south-east. Figure 1 shows an exposure

rack with 3 of the 150 specimens in place.

Table 3. Average weather and air quality data for the various exposure sites

Average Average Total Total Suspended ^ annual

annualannual annual particulate

Exposure site pH*" relative temperature sunshine precipitation matter humidity

(percent) ideg F) (hours) (inches) (mgjm?) Kure Beach"* ... 4.9 77 60 2669 58 31 Washington 6.9 67 57 2576 39 108

Pittsburgh 6.7 68 50 2202 34 160 DaUas 7.3 63 66 2911 40 95 Los Angeles ... 6.4 62 66 3284 11 169

^ Averages from Air Sampling Network of the Department of Health, Education, and Welfare. The suspended particulate matter was collected on an 8 X 10-inch (20.3 X 25.4-cm) high volume

(40 to 50 cubic feet (1.1 to 1.4 cubic meters) per minute) air filter. The filters were collected at approximately two week intervals. The pH values in table 3 are the pH of the solutions formed by refluxing an 8 percent aliquot of the filter with 50 ml of distilled water and diluting to 80 ml. Averages for National Oceanographic and Atmospheric Administration. Data from Cape Hatteras, N.C, rather than Kure Beach, for which no data were available.

6
4. Results and Discussion

4.1. Cleaning of Specimens

All specimens remaining in the test were returned

to the laboratory for inspection after they had been

exposed for 15 years. Upon arrival, each specimen was scoured for 30 strokes with a soft cellulose sponge that had been moistened with a one percent,

by weight, solution of trisodium phosphate and sprinkled with calcium carbonate. The specimens were

then rinsed successively with tap water, distilled water and ethyl alcohol. This cleaning treatment was

sufficient to clean the specimens exposed at all sites except Pittsburgh. The specimens from Pitts- burgh were vigorously scoured with calcium car- bonate until the surfaces appeared clean. They were

then rinsed with tap water, distilled water and ethyl

alcohol.

4.2. Corrosion of the Base Metal

After the specimens were cleaned, they were examined for corrosion of the base metal. None of the enamels on steel exposed at Pittsburgh or Dallas

showed any signs of corrosion of the base metal.

One enamel exposed at Washington, one at Los

Angeles, 34 at Kure Beach-800, and 39 at Kure

Beach-80 showed some rusting of the base metal.

The one enamel that permitted rusting at these four

sites was a 1000° F enamel on steel (Y-1). Since

there were only two enamels of this type included

in this test, more exposure testing is needed before

they should be recommended for outdoor exposure

applications.

The other enamels that permitted rusting at the

Kure Beach sites were not confined to any one enamel type but generally appeared to be specimens

which had pinhole-type defects or blisters present

prior to exposure. Since none of these specimens

showed any signs of rust until the seven-year in- spection, it seems probable that a thin layer of a high iron content glass existed at the bottom of the

defect which gradually corroded away during ex- posure to the weather.

The two exceptions to this pinhole-type rusting were enamels B-1, and B-2 exposed at Kure

Beach-80. The cover coats of these enamels

were completely eroded after 15 years' exposure,

and the remaining ground coat was not corrosion

resistant enough to protect the metal from rusting.

Thus, for severe environments, such as Kure Beach80, only the enamels with good acid and alkali resistance should be used.

It is interesting to note that 25 of the 39 enamels

which had permitted rusting during 15 years'

exposure at Kure Beach-80, had also shown rust on the enamel surface after 7 years' exposure. However, only one of these enamels, M-4, had permitted

the base metal to corrode through with the additional

8 years' exposure.

4.3. Measurements of doss and Color After

15 Years

The degree of weathering was evaluated by

changes in color and 45 degree specular gloss. The

gloss [8] is reported as the percentage of initial gloss retained after exposure, and the color is re- ported as color retention, which is 100 minus the

color change in NBS units [9]. The individual gloss and color retention values for each enamel after 15 years' exposure are presented

in table 1. In later tables and figures, the white

porcelain enamels were not included when computing average color changes, since white enamels nor- mally retain their initial color even after relatively severe surface attack. The screening paste enamels were also excluded from the averages because of

their abnormally large color changes. Also, the gloss

and color values for enamels K-3, N-1, N-2, Y-1

and Z-1 were excluded from the averages for enamels exposed at Kure Beach, because these

specimens were not reexposed after the seven year

inspection because of severe surface degradation.

4.4. Effect of Exposure Time on Changes in

Gloss and Color

The effect of exposure time on gloss and color

retention is illustrated in figures 2 and 3. The gloss

data in figure 2 indicate that the greatest gloss loss occurs during the first 2 to 4 years' exposure after which, for most locations, it tends to reach a constant rate. The data between three and fifteen years were extrapolated (as shown by the dashed lines in figure 2) to give predicted gloss retention values

after 30 years' exposure. (The next inspection of these enamels is tentatively scheduled after 30

years' exposure.) These extrapolated data indicate

that the enamels at the four milder sites, Pitts- burgh, Los Angeles, Dallas and Washington, would

be expected to have good gloss retention after 30

years' exposure, while the enamels exposed at the two sites at Kure Beach would be expected to have their original fire-polished surface completely

removed after 30 years' exposure. The slight in- crease in gloss is probably a result of the polishing

action required to clean the specimens exposed at Pittsburgh.

The color data shown in figure 3 indicate that the

greatest color changes occur during the first one to two years' exposure. After this, the color changes at

The tristimulus color difference parameters, L (lightnessdarkness), a (red- green), and b (yellow-blue) were measured with

a color difference meter. The color change, in NBS Units, was

calculated by the following formula:

Color Change (Zif) = VAZ,^ + Aa^ + Ai^

where L is lOVRd,

and Rd is the 45°, 0° luminous daylight reflectance.

7
8
a nearly constant rate which depends on the site. The color data between three and fifteen years were

extrapolated to 30 years. These extrapolations

showed the same trend as the gloss did. The

enamel at the four milder sites changed only about

4 NBS units in the additional 15 years' exposure,

while the enamels exposed at the Kure Beach sites changed about twice that much. The dirt on the

enamels exposed at Pittsburgh may have protected

the surface from color changes.

4.5. Compairson of Exposure Sites

Table 4 gives the average percentage gloss

retained and color retention for each exposure site. The gloss values are for all enamels except the

screening pastes, while the color values are for all nonwhite enamels except the screening pastes.

The gloss data in table 1 were ranked to deter- mine if there were significant differences between

sites. This analysis showed that no differences

(significant at the 5% level) existed between Pitts- burgh, Los Angeles and Dallas. However, the re- maining three sites, Kure Beach- 80, Kure Beach800 and Washington, were significantly different

from these three sites and from each other. This

Table 4. Average color retention and percentage gloss retained

after 15 years' exposure

Exposure site Color Gloss

retention " retained

{percent) Kure Beach-80 87.3 24.4 Kure Beach-800 89.7 33.3 Washington 92.9 59.8 Pittsburgh 94.7 76.4 Los Angeles 94.3 81.3 DaUas 95.5 77.4

" Color retention is given for all nonwhite enamels except

'screening pastes. Percentage gloss retained is given for all enamels except

screening pastes.

ranking again suggests the effectiveness of the dirt film in protecting the enamel surface on the speci- mens exposed at Pittsburgh from change since the

ranking of this site has changed from moderate to mild between the 3 and 1.5 year inspections.

The differences in the durability of the enamels

exposed at the various sites are undoubtedly caused

by differences in the atmospheres at the exposure

sites. After seven years' exposure [7], it was found

that the differences in gloss and color retention for the enamels exposed at the various sites correlated

fairly well with the average pH of a solution formed

by dissolving an 8 percent aliquot of the collected

suspended particulate matter in 80 cc of distilled water, and the average relative humidity at the

exposure site. This finding still appears to be valid

after 15 years' exposure as illustrated in figures 4

through 7. It seems likely that the atmospheric

moisture condenses on the surface of the porcelain

enamel, dissolving some of the particulate matter which had settled there. The solution thus formed,

having varying pH values as indicated in table 3

would then attack the enamel surface.

PITTSBURGH O WASHINGTON

•4.5 5,0 5.5 6.0 6.5 7.0 7 5 8.0 AVERAGE rH FROM THE NATIONAL AIR SAMPLING NETWORK Figure 5. Effect of pH of the particulate matter on the average

color retention of the nonwhite glossy enamels on steel.

O PinSBURGH

O WASHINGTON

4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 AVERAGE pH FROM THE NATIONAL AIR SAMPLING NETWORK Figure 4. Effect of pH of particulate matter on the average

gloss retention of the glossy enamels on steel.

1 1 1

DALLAS

1 1 1

LOS O PITTSBURGH ANGELES ^s.^ - washingtonO \v

1 1 1

^)vJ<URE BEACH

1 l\ 1 68 72 76 8 AVEIACE RELATIVE HUMIDITY Figure 6. Effect of average site humidity on the average gloss retention values for the glossy enamels on steel.
'1 1 1 1 1

Q DALLAS

1

OlOS~\ *^ PinSBURGH

ANGELES _ WASHINGTON ^^^^

— KURE BEACH

1 1 1 1 1 68 72 76 8 AVERAGE REIATIVE HUMIDITY Figure 7. Effect of average site humidify on the average color

retention for nonwhite glossy enamels on steel.

4.6. Comparison of Enamel Types

The average color and gloss retention at all sites for each enamel type is given in table 5. The enamel

types are ranked according to average color retention. These data indicate that the glossy, acidresistant enamels on steel had the best color

retentions, while the glossy enamels on aluminum

had the worst color retentions. However, the

rankings of the last four enamel types may be in error since many of the enamels exposed at Kure

Beach-80, the most severe site, were not included

in these averages because they were not re-exposed

after the 7-year inspection.

The average gloss and color retention values for the porcelain enamels on aluminum were much

lower than had been anticipated. However, these

enamels were among the first commercially avail- able porcelain enamels for aluminum. There have

been many improvements in the enamel formulations since this test was started in 1956. A test of these newer improved porcelain enamels on aluminum initiated in 1964 showed marked improvements

in gloss and color retention [10, 11]. Table 5. Average color retention and percentage gloss retained for the eight types of enamels

Enamel type

Regular glossy on AR=»

1300 T on steel Matte on steel Matte on aluminum.

Regular glossy on Non-ARi1000 °F on steel Screening paste enamels

Glossy on aluminum

teel.

teel.

Color

retention Percentage

gloss retained

95.6 67.8

94.4 69.4

94.2 57.5 93.0 66.6

90.0 50.3

85.3 71.8 83.9 70.0 83.0 47.6

^ Enamels with citric acid spot test ratings of AA, A or B are designated as AR (acid-resistant), while those with C and D

ratings are designated as Non-AR (non-acid-resistant). These averages exclude the values for three enamels (K-3, N-1, and W-2) exposed at Kure Beach-80 which were removed

from further testing after 7 years exposure. These averages exclude the values for enamels exposed at Kure Beach-80 since these enamels were removed from further

testing after 7 years exposure.

4.7. Correlation of Weather Resistance With

Acid Resistance

The primary accelerated test used to predict the

weather resistance of porcelain enamels is the

citric acid spot test [12]. This test divides the enamels into five categories having the alphabetical

designations AA, A, B, C or D. The enamels recom- mended for exterior architectural applications are those designated AA or A. The 15-year color and gloss data for glossy

enamels on steel indicate that the AA and A

enamels have, on the average, the best gloss and

color retentions. This is illustrated for the enamels

exposed at Washington (figures 8 and 9). These

data also indicate that there is considerable scatter

in the enamels designated C or D and that several

of these enamels had i gloss ' and I color retentions

as high as those designated A or AA. In addition,

the citric acid spot test is difficult to evaluate on

matte enamels. Therefore, the color data were

plotted as a function of the enamels' boihng acid

solubility [13]. These data are illustrated for both

the glossy and matte enamels on steel exposed at Washington in figure 10.

1 I 1

1

» 6

0

1 1

0 ^•^^ -

0

o o ~ ABC1 1 1

CITRIC ACID SPOT TEST RATINO

Figure 8. Correlation between citric acid spot test ratings and

weather resistance as measured by gloss retention for the glossy enamels on steel exposed at Washington.

ARC CITRIC ACID SPOT TEST RATING Figure 9. Correlation between citric acid spot test ratings and

weather resistance as measured by color retention for the glossy enamels on steel exposed at Washington.

10
too

90

60

TBB* ' o o

'

1 1

1

1

1

I A A

A A

A A -

o —

o" o — • GLOSSY ACID RESISTANT ENAMELS o

o -

O GLOSSY NONACID RESISTANT ENAMELS A MATTl ENAMELS

1 1 1

1 1 11 1 '6 24 32 40 48 56 64 OILINO ACID SOLUIILITY, mg/ina

Figure 10. Correlation between the boiling acid solubility and weather resistance as measured by

color retention for the glossy and matte enamels on steel exposed at Washington.

More scatter was observed in these data than was

observed at 7-years' exposure [7]. However, the

enamels considered acid-resistant by this test (under 12 mg/in^ acid solubility) all had good color

retentions.

While the data illustrated are only for the enamels

exposed at Washington, the enamels exposed at the

other sites followed the same general pattern.

4.8 Cupric Sulfate Test for Predicting the

Color Retention of Red and Yellow Enamels

The cupric sulfate test to determine the color

retention of acid resistant red and yellow cadmiumselenium-sulfide pigmented enamels [14] was

developed after the first year inspection. This test has been successful, giving results which correlate

with color retention at all sites, for the acid-resistant

red and yellow screening paste enamels. The

average color retentions for the acid-resistant red

and yellow glossy enamels on steel which passed

this test are good. It therefore appears that this test

is a useful tool to evaluate the color retention of

these enamel colors.

4.9 Effect of Exposure Angle

It was felt that changing the exposure angle from

90° (vertical), as would be used in siding applications, to 45°, as might be found in roofing installa- tions, would greatly accelerate the weathering of the

enamels. Therefore, duplicate specimens of 44

enamels were exposed at 90° as well as 45° at Washington. The average color and gloss retentions

for these enamels are given in table 6. These data

indicate that changing the exposure angle from

90° to 45° does not significantly change the rate of

weathering of porcelain enamels at Washington.

4.10 Comparison with late 1930's enamels

Table 7 compares the average gloss and color

retentions for the regular enamels on steel exposed

for 15 years at Washington in this test and in the

test initiated in 1939. These data indicate that the

average color retention of the acid-resistant enamels

after 15 years' exposure varies by only 0.1 NBS

unit while the gloss retention differs by 6.1 percent

which is a barely discernable change. Thus, it may

be said that the new enamels for steel produced

in the early 1950's are equally resistant to weathering, as measured by changes in gloss and color, as those produced in the late 1930's.

Table 6. Comparison of the average gloss and color retentions for the enamels exposed at angles of 45° and 90° at Washington, D.C.

Exposure angle Gloss retained Color retention

(percent) 45° 57.7 92.4 90° (vertical) 61.7 93.9

Table 7. Comparison of 15-year results for enamels on steel from the 1939 and 1956 exposure tests

Exposure test Enamel type Color

retention Percentage

gloss retained

1956 AR"

Non-ARb AR«

Non-AR"

97.7

90.7 97.6

92.1

68.4

51.2

74.5 48.5

1956

1939

1939

" Same as table 5. Same as table 5.

11
5. Summary

After 15 years' exposure at Los Angeles, Cali- fornia; Dallas, Texas; Pittsburgh, Pennsylvania;

Washington, D.C.; and two sites at Kure Beach,

North Carolina, triplicate specimens of 91 porcelain

enamels were examined visually for corrosion of the

base metal and were measured for changes in gloss

and color. A summary of the more important

findings follows:

1. Comparison with enamel specimens exposed

for 15 years in an earlier test showed that procelain enamels produced in the early

1950's were equally resistant to changes in gloss and color as those produced in the

late 1930's.

2. The glossy acid-resistant enamels on steel were found to have the best weather re- sistance of the seven types of enamels in- cluded in this test.

3. A correlation was found between an enamel's

acid resistance as measured by either the

citric acid spot test or the boiling acid

solubility test, and weather resistance as measured by changes in gloss and color.

4. No significant difference was found in the

weathering of enamels exposed at 90°

and 45° to the horizontal, respectively, at Washington.

5. A correlation was found between both the pH

of the suspended particulate matter and the

average relative humidity at an exposure

site, and the changes in both gloss and color

of porcelain enamels exposed at that site.

6. The severity of the exposure conditions on the

enamel specimens was found to differ for different sites, except those at Pittsburgh,

Los Angeles, and Dallas were similar. The

sites in order from most severe to mildest were: Kure Beach-80, Kure Beach-800,

Washington, and (Pittsburgh, Los Angeles

and Dallas).

7. No corrosion of the base metal Was noted on any of the enamels exposed at Dallas or

Pittsburgh. One enamel exposed at Washington and one at Los Angeles showed

rusting of the base metal, while 34 enamels

at Kure Beach-800, and 39 enamels at Kure

Beach-80 permitted the base metal to rust.

8. All specimens could be cleaned easily except

those exposed at Pittsburgh. The adherent

dirt film on the enamels exposed at Pitts- burgh appears to have protected the enamel

from weathering action.

6. References

[1] Harrison, W. N., and Moore, D. G., Weather resistance of porcelain enameled iron structural units, J. Research,

NBS 28, 735 (1942) RP1476.

[2] Harrison. W. N., and Moore, D. G., Weather resistance of porcelain enamels exposed for seven years, J. Research,

NBS 42, 43 (1949) RP1949.

[3] Moore, D. G., and Harrison, W. N., Fifteen-year exposure

test of porcelain enamels, NBS Building Materials and

Structures Report 148 (1957).

[4] Baker, M. A., 1939 Exposure test of porcelain enamels on

steel, 30-year inspection, Nat. Bur. Stand. (U.S.), Bldg.

Sci. Ser. 38, 9 pages (Aug. 1971).

[5] Potter, Alan, First-year data on weather resistance of screening-paste enamels, Proc. Porcelain Enamel Inst. Forum 19. 131 (1957). Porcelain Enamel Institute, 1900 L St. N.W., Washington, D.C. 20036.

[6] Moore, D. G., and Potter, Alan, Effect of exposure site on weather resistance of porcelain enamels exposed for three years, Nat. Bur. Stand. (U.S.), Monogr. 44, 13 pages

(Apr. 1962).

[7] Rushmer, M. A., and Burdick, M. D., Weather resistance 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).

[8] Standard Method of Test for 45-Deg. Specular gloss of ceramic materials, ASTM Designation: C346, ASTM Book

of Stantards, Pt. 13 (1973).

[9] Hunter, R. S., Photoelectric tristimulus colorimetry with

three fihers, NBS Circ. 429, 48 (1942).

[10] Baker, M. A., 1964 Exposure test of porcelain enamels on aluminum, three year inspection, Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 29, 13 pages (Apr. 1970).

[11] Baker, M. A., Weatherability of porcelain enamels, Applied

Session Technical Papers, Aluminum Finishing Seminar

(1973). The Aluminum Association, 750 Third Avenue,

New York, New York 10017.

[12] Acid resistance of porcelain enamels (citric acid spot test), C-282, ASTM Book of Standards, Pt. 13 (1973).

[13] Resistance of porcelain enameled utensils to boiling acid, C-283, ASTM Book of Standards, Pt. 13 (1973).

[14] Cupric sulfate test for color retention, PEI Bulletin T-22,

Porcelain Enamel Inst. Inc., 1900 L St. NW., Washington,

D.C. 20036.

12

ft U. S. GOVERNMENT PRINTING OFFICE : 1974 O - 539- 878
HBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUHI.K A riON OK Ki;P()R r NO. NBS BSS-50

2. Gov't Acccs.sion No.

3, Recipient's Acccs.sion No.

4. TITLE AND SUBTITLE

The Weather Resistance of Porcelain Enamels - 15-Year Inspection of the 1956 Exposure Test

5. Publication Date Julv 1974

6. (Performing Organization Gode

7. AUTHOR(S)

Margaret A. Baker

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Projcct/Task/Work Unit No. 4616571

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Porcelain Enamel Institute

1900 L Street, NW

Washington, D. C. 20036

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 74-600034

16. ABSTRACT (A 200-word or less [actual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) In 1956, an exposure test of porcelain enamels at 4 urban and 2 ocean shore sites

in the continental United States was initiated by the National Bureau of Standards

and the Porcelain Enamel Institute. After fifteen years, all exposed specimens were returned to the Bureau and the changes in gloss and color determined. The gloss

changes were found to be significantly different at all exposure sites except

Pittsburgh, Los Angeles and Dallas. The most severe changes occurred at the Kure

Beach, North Carolina, site nearest the ocean, while the least changes occurred at

Pittsburgh, Los Angeles and Dallas. The differences in behavior of the specimens

correlated with both the average relative humidity and the pH of the suspended

particulate matter at the different sites.

A correlation appeared to exist between the acid resistance of the enamels and

changes in gloss and color. The regular, glossy, acid-resistant enamels on steel

showed the best weather resistance of the various types tested.

Comparison with enamel specimens exposed for fifteen years in an earlier test

showed that porcelain enamels produced in the early 1950 's were equally resistant to

changes in gloss and color as those produced in the late 1930' s.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Acid resistance; color; gloss; pH; porcelain enamel; relative humidity;

weather resistance.

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