ASTM C282-20

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C282 − 10 (Reapproved 2015) C282 − 20
Standard Test Method for
Acid Resistance of Porcelain Enamels
(Citric Acid Spot Test)
This standard is issued under the fixed designation C282; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
INTRODUCTION
The described method furnishes a means of testing and grading glossy porcelain enamels with
respect to their resistance to citric acid at room temperature. Citric acid has been selected because it
is the most common and one of the more severe of the food acids in its action on conventional
porcelain enamels. The degree of etching by a citric acid solution provides a good indication of the
susceptibility of attack of a porcelain enamel coating to common food-based acids.
1. Scope
1.1 This test method covers a procedure for evaluating porcelain enamels in their resistance to citric acid exposure at room
temperature. No attempt is made to categorize porcelain enamels as to their acid-resistance or non acid-resistance properties, since
the requirements in the several branches of the industry differ.
1.2 The test method is applicable for ware of various shapes providing they contain a substantially flat area approximately 50 mm
in diameter.
1.3 The test method is not applicable to finishes on chemical and hospital ware, which may come in contact with strong mineral
acids, nor to cooking utensils, which may come in prolonged contact with hot acid solutions.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Summary of Test Method
2.1 The test method consists of a 15 min exposure of the test surface to a small pool of 10 % citric acid, and an evaluation of the
effect in terms of the change in appearance and the “relative cleanability” of the surface resulting from the treatment.
This test method is under the jurisdiction of ASTM Committee B08 on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.12 on
Materials for Porcelain Enamel and Ceramic-Metal Systems.
Current edition approved May 1, 2015Nov. 1, 2020. Published May 2015December 2020. Originally approved in 1951. Last previous edition approved in 20102015 as
C282 – 10.C282 – 10(2015). DOI: 10.1520/C0282-10R15.10.1520/C0282-20.
This test method is based on the Test for Acid Resistance of Porcelain Enamels (Citric Acid Spot Test) Bulletin T-21, of the Porcelain Enamel Institute.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C282 − 20
3. Significance and Use
3.1 This test method is intended specifically for testing the porcelain enamel finish on stoves, refrigerators, table tops, sinks, and
other sanitary ware, laundry appliances, architectural units, etc., where the surface may come in contact with food acids at room
temperature.
3.2 Citric acid has been chosen as the test medium because it is one of the most common of the food acids and will generally
provide a measurable result in its action on porcelain enamel.
4. Apparatus
4.1 Dropper Bottle, or medicine dropper,
4.2 Watch Glass, 25 mm in diameter with fire polished edge,
4.3 Towel, soft cotton, and
4.4 Drafting Pencil, conventional graphite, degree 3B.
5. Reagents and Materials
5.1 Citric Acid Solution—Dissolve 10 g of anhydrous citric acid crystals (H C H O ) in 100 mL of water. distilled water or water
3 6 5 7
of equivalent purity. Solution shall be prepared not more than 48 h prior to use.
5.2 Cleaner Solution—Dissolve 10 g of trisodium phosphate (Na PO ) in 1 L of tap water.
3 4
6. Sampling
6.1 The test specimens may be articles of commerce, pieces cut from articles of commerce, or laboratory specimens prepared
especially for this test.
NOTE 1—Processing variables in the application and drying and firing operations materially affect the degree of attack by the acid on the surface of
porcelain enamels. Sample specimens used for classification of acid resistance must be processed under identical conditions to the commercial ware they
represent.
7. Procedure
7.1 Thoroughly wash area to be tested using a soft cotton towel moistened with a warm, 1 % solution of trisodium phosphate.
Rinse in warm, running tap water, and dry with a soft towel by blotting. Store the specimen at a temperature of 26 6 1°C1 °C (79
6 2°F)2 °F) for a time sufficient to bring it within this range prior to and during the test.
NOTE 2—If, when rinsing, the water gathers in drops on the surface, repeat washing treatment until water spreads evenly.
7.2 On articles of commerce, select areas that are horizontal or nearly horizontal in service. Place the specimen in a position such
that a flat area at least 38.1 mm in diameter is horizontal. With the specimen and the citric acid solution at 26 6 1°C1 °C (79 6
2°F),2 °F), place several drops of the solution on the test area to form a pool, and immediately cover with a clean watch glass in
the inverted position. Use a quantity of solution that is just sufficient to fill the inverted watch glass except for a small air bubble
(three to six drops are usually required, depending upon the dropper and the curvature of the watch glass). After 15 min15 min
630 s of treatment, remove the watch glass and immediately rinse the spot of solution from the surface. Dry the specimen with
a dry, clean, soft cotton towel by blotting (not rubbing).
NOTE 3—The test surface must be thoroughly dry before grading. The presence of a slight film of water on the surface may change the rating of specimens
near the borderline between classes.
C28
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