ASTM_E_2808_-_11.pdf

Designation:E280811Standard Guide forMicrospectrophotometry and Color Measurement inForensic Paint Analysis1This standard is issued under the fixed designation E2808;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONColor is one of the most important comparative characteristics of paints.The comparison of coloris one of the first steps taken in a forensic paint comparison and it is essential to note that this guidedoes not propose the use of instrumental color comparison for objects that are distinguishable to theeye.Since the 1940s,analytical instruments have been able to discriminate colors that the averagehuman eye cannot distinguish.Microspectrophotometers(MSPs),in particular,allow for an objectivemeasurement of the color of small,millimetre or submillimetre samples and are more precise orquantitative compared to the more subjective results of visual microscopical color comparisons.Suitable instruments with appropriate optics,sensitivity,resolution,and dynamic range can measureand produce spectral curves of light energy from small samples as that light is transmitted,absorbed,or reflected by the sample.These spectra are collected over small measurement steps or increments ofone-half to a few nanometers each.MSPs typically operate in the visible spectral region(380 to800 nm)and also in the ultraviolet region(190 to 380 nm).They should not be confused withbroadband or absorption filter-based,tristimulus systems or low-resolution,large measurement step(5 nm or more)spectral analyzers.The spectral limits of different instruments can vary in all of the above noted spectral regions andmay also include the near infrared region from about 780 to 2100 nm.The usefulness of this lastspectral region in the analysis and comparison of paint fragments is currently indeterminate and willnot be covered in this guide.Subjective terms such as“blue,“violet,”or“purple”are inadequate descriptors of actual color.MSPinstruments can be used to describe or numerically“name”an items color by calculating the itemscolorimetric values.These values,or chromaticity coordinates,can be expressed in any one of severalcoordinate systems and are useful in the development and maintenance of color comparison databases.Colorimetric values are of limited use in actual color comparison of evidence samples becausediffering spectral curves can yield identical colorimetric values.This is commonly found in industrialor commercial paint-matching protocols in which the only requirement is to paint an item so it appearsto be the same as others.The eyes perception and the colorimetric values of two items may indicatethat they are the same color,but the spectral curves of those items may still be distinguished.Thisleads to the use of the MSP in the comparison of visually indistinguishable colored items.1.Scope1.1 This guide is intended to assist individuals and labora-tories that conduct forensic visible and ultraviolet(UV)spec-tral analyses on small fragments of paint using Guide E1610.1.2 This guide deals primarily with color measurementswithin the visible spectral range but will also include somedetails concerning measurements in the UV range.1.3 This guide does not address other areas of color evalu-ation such as paint surface texture or paint pigment particlesize,shape,or dispersion within a paint film that are evaluatedby other forms of microscopy.Other techniques such asspectral luminescence,fluorescence,and near infrared(NIR)are not included in this guide because of their limited use,lackof validation,or established efficacy in forensic paint analysis.1.4 This guide is directed at the color analysis of commer-cially prepared paints and coatings.It does not address theanalysis or determination of provenance of artistic,historical,or restorative paints,but it may be found useful in those fields.1This guide is under the jurisdiction of ASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved March 1,2011.Published May 2011.DOI:10.1520/E2808-11.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 1.5 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D16 Terminology for Paint,Related Coatings,Materials,andApplicationsD1535 Practice for Specifying Color by the Munsell SystemD2244