ASTM D3964-10(R2020) pdf free download
ASTM D3964-10(R2020) pdf free download.Standard Practice for Selection of Coating Specimens for Appearance Measurements
1. Scope
1.1 This practice provides a guide to selection of specimens for appearance measurement by reflected light as well as a discussion of factors to be considered in their preparation for measurement. Standardized selection and presentation proce- dures will assist in achieving agreement between evaluations carried out in different laboratories as well as helping to achieve better correlations between visual evaluations and instrumental measurements. N OTE 1—This standard is not a practice for preparation oftest panels of coatings; see Practices D823. 1.2 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 appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.3 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
5. General Requirements
5.1 Selection—In making appearance measurements it is important that the specimens selected be representative of the material of interest. Once selected, the specimens must be carefully examined to determine if they are suitable for measurement, and if not, they must be cleaned or otherwise prepared. Careful attention to these factors is necessary if the measurements are to be valid. 5.2 Specimen Size—The minimum size is dictated by the size of the specimen port of the instrument to be used for measurement. When an instrument provides a choice of speci- men port sizes, use the largest port that can be completely covered by the specimen. A large measured area helps to minimize the effect of any small area nonuniformity and is therefore more likely to provide results that agree with the involuntary averaging that takes place when specimens are observed visually. In addition, a large specimen also permits the operator to make measurements on several areas of the specimen when desired, thereby providing further specimen averaging. 5.3 Opacity—For determination ofgloss or color, an opaque specimen shall be selected whenever possible. When the specimen is translucent or transparent, the following practices shall be implemented: 5.3.1 For Gloss Evaluation—The specimen shall preferably be sufficiently thick that a secondary reflection from the back or second surface of the specimen cannot enter the receptor optics of the glossmeter. When thin transparent specimens must be measured, adopt one of the following procedures:5.3.1.1 Back the specimen with a light-absorbing material of the same refractive index as the specimen, and in optical contact with it. 5.3.1.2 Use an agreed-upon specimen thickness, including coating and substrate, and place a black backing behind the specimen. 5.3.2 For Color Evaluation—The choice of backing of even slightly translucent specimens will affect their measurement. Use the most applicable of the backing techniques that follow. In each case it is essential that the backing material and color be reproducible, stable, and durable for reliable results. 5.3.2.1 Back the specimen with the same material with which it will be backed in its intended use. 5.3.2.2 Back the specimen with identical or similar material. 5.3.2.3 Back the specimen with a neutral material whose luminous reflectance is essentially the same as that of the specimen being evaluated. 5.3.2.4 Back the specimen with a black surface such as a painted panel or black glass. 5.3.2.5 Back the specimen with a white backing of known reflectance.
