White32 Glass Color Standards

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Reprinted fromJ ournal of the Association 0/ Official Agricultural ChemistsNovember, 1956

GLASS COLOR STANDARDS FOR EXTRACTED HONEYBy B. A. BRICE,A. TURNER,JR.,tand J. W. WHITE,JR. (Eastern

Regional Research Laboratory.j Philadelphia 18, Pa.)The colorsof commercial extracted honeys, in thicknesses of about 30

mm, range continuously froma pale yellow through amber to deep redoreven black, depending onfloral sourceand composition. In general, thelighter colors are associated with delicate flavors and the darker colorswith strong flavors and less attractive appearance, It is natural, then,that colorhas been for many years afactor in the grading andmarketingofhoney. In 1925the Department ofAgriculture established gradestand-ards for extracted honey and adopted the Pfund Color Grader for elassi-ficationof its color (1, 2). Thecolorclassesweredesignated Water White,Extra White, White, Extra Light Amber, Light Amber, Amber, andDark. Theboundaries orcut-off points between these classesweredefinedin terms of selected scale readings (3) on the Pfund instrument, corre-sponding to settings of an amber glass wedge that furnishes a one-dimensional scaleof chromaticity. Extracted honeymay exhibit turbidityin varying degrees dueprimarily to colloidal matter and pollen, but thisaspect of appearance is ignored in classificationfor color,whichisdoneonthe basis of chromaticity only.In the Pfund Color Grader the sample of honey is placed in awedge-shaped glasscell, which ismounted abovethe amber glasswedgeand on

the same movable metal frame. The gradients of the wedges are inopposite sense. Narrow vertical portions of the wedges are viewed, oneabove the other, through rectangular apertures (5.5X 16mm, with an8mm dividing line). The usual illuminant is a 200watt lamp, diffusor,and daylight filter. The wedges are moved simultaneously by rack andpinionuntil thenearest chromaticity match isobtained, and their positionis read fromamillimeter scale. If the average scale reading is 8mmorless, the sample is classifiedWater White; if 16.5mmor lessbut greaterthan 8, Extra White; if 34mmor lessbut greater than 16.5,White; if 50mmor lessbut greater than 34, Extra Light Amber; if 85mmor lessbutgreater than 50, Light Amber; if 114mm or less but greater than 85,Amber; if greater than 114mm, the sample is classifiedas Dark. A cor-rection chart has usually been supplied with each instrument so thatreadings could be referred to those obtained on a standard instrumentfitted with the primary standard wedge.'

IIIPresented in part before the Optical Society of America, Boaton, Massachusetts, October 9-11,1952: .T.Opl. Soc. Am 42.881 (952) (Abstract).Presented at the Seventieth Annual Meeting of the Association of Official Agricultural Chemst Oct..15-17. 1956. at Washington. D. C.t Present address: Smith, Kline and French Laboratories, Philadelphia. Pa.~A laboratory of the Eastern Utilization Research Branch. Agricultural Research Service. U. S. De-pa.rtment of Agriculture.1 Until recently. distribution and calibration of this instrument werehandled by the MUDBellColorCompany. Baltimore. Md. This is now done by the manufacturer, Koehler Instrument Company, 168-56Douglas Avenue. Jamaica. N. Y.


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920 ASSOCIATION OF OFl


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1956] BRICE et al.: GLASS COLOR STANDARDS FOR HONEY 921metric studies, and the 31.5mmthickness wasusedfor final colormatch-ingof solutionswith glasses. For routine colorclassificationsquarebottlesof31.5mminternal thickness wereadopted. This squarebottle isthesamecontainer used for color classificationof maple sirup (5), made by HazelAtlas Glass Company under the designation No. 2653 French squaretablet bottle, 1! inch square, 2 ounce capacity.Pfund ColorGrader.-The standard Pfund ColorGrader No. 100 fittedwith the primary standard wedgewas used at the Munsell Color Com-pany, Baltimore, Md. Pfund Color Grader No. 441, exhaustively cali-brated by the authors directly against the standard equipment at Balti-more, wasusedat this laboratory.Polarization Photometer.-Final color matching of standard solutionsand glasses was done with a polarization photometer (7, pp. 157-159)

equipped with a 6 circular fieldand with CIE Illuminant C, an incan-descent lamp operated at a color temperature near 2854K, plus Davis-Gibson filters (8).Spectrophotometer.-Spectrophotometric nomenclature followed isthat used in the sugar industry (9, 10) and differsonly slightly fromthatrecommended by the A.O.A.C. (11). Measurements of spectral trans-mittance weremade on a General Electric recording spectrophotometerfrom400 to 750mIL and insomecasesonaBeckman DU spectrophotome-ter from380 to 400mIL.Wavelength errors onthe former instrument werejudged not to exceed 0.5 mIL(at least from 440 to 700 mIL)by testswithadidymium filter (12) andwithglassfiltersstandardized for spectraltransmittance by the National Bureau of Standards (13). In these testsand in measuring the transmittancy of solutions and transmittance ofglasses for final colorimetric analysis; values were read from the instru-ment dial rather than fromcontinuous recordings. Whenever avaluewasbelow about 0.11, amore accurate transmittancy or transmittance wascalculated fromameasurement onathinner layer of solution or glass.ClE Colorimetric Data.-Color specifications based on the 1931 CIEstandard observer (7, 8) and Illuminant C for the final standard solutionsand final glass color standards were calculated by using the weightedordinate method of integration at 10 mIL intervals from 380 to 760 mIL.CIE data foranumber of samples of extracted honey wereevaluated lessaccurately fromrecorded transmittancy curves with the aid of aGeneralElectric semi-automatic tristimulus integrator and the method of 30selected ordinates.

CHARACTERIZATION OF HONEYS AND CARAMEL SOLUTIONSThe spectral characteristics of typical clarified extracted honeys and

two caramel-glycerin solutions areshownin Fig. 1,plotted asabsorbancyversus wavelength, both on logarithmic scales. The data werecalculatedto a sample thickness of 31.5 mmfromtransmittance measurements in


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922 ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS [Vol. 39, No.4-thinner cells, with glycerin as a referencemedium. The shapes of spectralcurves plotted in this way depend only on the nature of the pigments orcolorants present, and not on their concentration or on the thickness ofthe sample. A rough characterization of colorant identity, in the absenceof appreciable turbidity, is provided by a ratio of absorbancies at twowavelengths. This wastermed a"Q-ratio" by Peters and Phelps (14)whenone of the wavelengths chosen was 560ms, and was used by them toi s . . . - - - - - - r - - - - - - - , . . - - - - . . , . . - - . .

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FIG. i.-Spectral characteristics of typical clarified extracted honeys (curves1-6) and caramel-glycerin solutions (curves A and B). Absorbancy and wavelengthare both plotted on logarithmc scales. All data calculated to a thickness of 31.5mm,with glycerin as a reference.determine whether agiven filtered sugar solution deviated from"normal"inspectral character. A morecompletecharacterization studied by Liggettand Deitz (15) was the slope or "wavelength exponent" of the approxi-mately linear curve relating logarithm of absorbancy and logarithm ofwavelength. They showed that when these curves areaccurately linear inthe visible spectrum, they can be completely characterized by the wave-length exponent and the absorbancy index (attenuancy index if turbidityis present) at onewavelength, usually chosen as 560mj.l.Data forabsorbancy ratios (at wavelengths 500and 560mu) andwave-

length exponents for extracted honey, maple sirup (5), caramel-glycerin


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solutions (5), and limited data for filtered sugar solutions, are assembledin Table 1. These data and curves such as shown in Fig. 1suggest thattheprincipal colorants ofhoney!maple sirup, caramel solutions, and othersugar products aresimilar. Minor irregularities in the log A versus logXcurves (perhaps most pronounced in honey because of the possiblepresence of floral pigments), and variations in the data of Table 1, in-dicate minor variations in colorant composition in all these products.This variation is further shown by scattering of points in the CIEchromaticity diagram for honey and caramel solutions (Fig. 3), maplesirup (5), and sugar liquors (15, p. 266). The colorsof none of these prod-ucts arestrictly one-dimensional with respect to chromaticity. A previousstudy of someof the spectral characteristics ofhoney wasmadeby Phillips(16), but these data are of little practical use. A good discussion of thecolorants in sugar products is given by Liggett and Deitz (15).Caramel-glycerin solutions were used instead of honey in the stand-

ardization phases of the present investigation for the following reasons:They are shown by Fig. 1and Table 1to be good spectral matches forhoney; they are free from variations in turbidity; and they are moreeasily adjusted to adesired color. Sixstandard caramel-glycerin solutionswereprepared and carefully adjusted until average wedgesettings for thefinal solutions ontwo Pfund Color Graders (including the primary stand-ard) did not differ significantly from the nominal standard settings (3).The results are shown in Table 2. The average standard deviation fromthe mean of 10settings (for oneof the authors, B.A.B.) was 0.36 mmand wasnearly constant over the entire range of wedgesettings. For thisobserver, the means of two groups of 10settings would have to differ byabout 0.7mmtobesignificantly different.The six final solutions of Table 2wereassumed to typify the Depart-

ment's color standards for extracted honey in respect to appearance!spectral character, and specifiedcut-off points onthe Pfund Color Grader.These "standard" solutions were further characterized in a number ofways, as indicated in Table 3, forpurposes of comparison with other colorscales. The reference medium for the spectral and CIE data was clearcolorless glass;' to compensate for reflection losses only and to permitcharacterization of the whole solution rather than the solute. The datainclude the basis for calculating cut-off points on three abridged or one-dimensional colorscalesused in the sugar industry. "Color Indexes" usedfor filtered sugar solutions are 1000A420/bc (17, 18)and 1000A660/bc (17)or simply A660/bc (19, 20), where A is the absorbancy of the solution atthewavelength (mu) indicated by the subscript, b is the thickness of solu-tion and reference (usually water) in ern, and c is the concentration ofsugar solids in g/rnl, A widely used "Compensated Color Index" applica-

Distilled water as a referencewould giveessentially the Same results but would be less satisfactoryat wavelengths greater than 700mI'.


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FIG. 2.-Spectral transmttance of "standard" caramel-glycerin solutions(dotted curves) in cellsof31.5mminternal thickness, relative to that of clear glass;andspectral transmttance ofglasscolorstandards (solidcurves) matching thecolorsof the respectivesolutions.government inspection agencies and the industry for duplicate sets ofstandards. Because of small variations of color ordinarily present withina given melt of glass, and because of unavoidable deviations fromthick-ness specifications in grinding and polishing operations, it was necessaryto establish color tolerances and a simple procedure for testing duplicatestandards.Sixseriesof glasseswereselected, oneseriesfor eachof the color stand-ards, in which the individual piecesdifferedsignificantly intransmttancerelative to that of the master standard at aselected wavelength. For con-venience, the wavelength selected (except for the Amber standard) wasthat showingatransmttance of 30.0per cent for the master standard. Ingeneral the transmttances of the glasses in a series ranged from about28per cent to 32per cent, the extremes including glasses considered notacceptable as color matches for the master standards. From each series,glasses representing acceptable "light" and "dark" limts were selectedby visual comparison of each glass with a master standard. The glasses(37mmsquare) wereheld in closejuxtaposition 12to 18inches fromtheeye, or wereheld as filters closeto the eye in quick succession; overcastsky was used as a source. These conditions are comparable with thosepreferred for color classification of extracted honey.

Spectral transmttances of all glassesin the series weremeasured, andtristimulus values and chromaticity coordinates were calculated forIllumnant C. The chromaticity difference between each glass and the

929


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1956J BRICE et al.: GLASS COLOR S'l'ANDARDS FOR HONEY 933fromTable 6that the tolerancesadopted for themapleand honey colorstandards areessentially equal.The measurement of transmttance of finished glassesat one wave-

length, with established tolerances in these units (Table 6), furnishes arapidmethodoftesting duplicatestandards foracceptability, and canbedoneby technicians inexperiencedin colormatching. Themethod is dif-ferential and henceessentially freefromerrorsofwavelengthand photo-metric scale. For the White color standard, for example, the spectro-photometer is set at a wavelength to indicate a transmttance of 30.0per cent with the master standard as a sample. The transmttances ofaseriesofduplicatestandards arethen measured inrapid successionandthosehavingtransmttances higher than 31.1per cent orlowerthan 28.9percentarerejected. (Forsometypesofspectrophotometers themeasure-mentsand data wouldbemoreconveniently expressedinterms of trans-mttance relative to that of themaster standard.)Thetechniquewasextendedalsotothe testingof stockglassesprior to

grindingandpolishingin order toreducethe number of rejections. Stockglasseswerecut into 37mmsquaresandplacedinthespectrophotometerat the wavelength required to show30.0per cent transmttance for themaster standard. Thethickness and transmttance of eachpiecewas re-corded. Thethickness required to giveatransmttance of 30.0per cent,and hencestandard color,wasthen quickly determned by referencetoa calculated curverelating transmttance (10to32per cent) to relativethickness (absorbancy ratio). This curveWasnearly linear and could beusedfor all the standards of Table 6 (exceptAmber) and for the maplestandards (5). For example, a stock glasswith a transmttance of 11.0per centwouldrequirethat itsmeasuredthicknessbereducedbyafactor0.526 (i.e., absorbancy ratio, corrected for surface reflection losses) inorder tohaveastandard transmttance of30,n per1f'cnli;Becauseofsmallcolorvariations withinsomeofthemelts, the calculatedthicknesswouldnot necessarily be the sameas the thicknesses of the.master standards(Table 5). Stockglassestestedinthisway wereplacedin groupshavingnearly the samepredictedihickness. Grinding andpolishingwerethenperformed batch-wiseonthese groups, and very fewrejections resultedunlessthicknesstolerances (Table6) wereexceeded.Aspecialprocedurewasrequiredforhandlingtheredcomponent ofthe

standard for Amber. This glasshad a steep transmttance curve from590-640m,uwith avery hightemperature coefficientoftransmttance inthis range; asaresult, the30per cent transmttance methodwasunrelia-ble. It wasfound, however, that lowtransmttances onthe broad toe ofthecurve(530-:-580mu)werelesssensitivetotemperature; also,bymeansof the polarization photometer, it wasfound that chromaticity matcheswerenot noticeably changedby relatively largetemperature changes.Asuccessful procedurefor testing thesecomponentswastomeasure trans-


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934 ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS [Vol. 39, No.4-mttance of aspecimenrelativeto that of themaster standard (TIT.) atthemercurywavelength578muinaspectrophotometer 01' filterphotome-ter (23)capableofmeasuringrelativetransmttances preciselyat greatlyreduced levels of illumnation (the transmttance of the standard com-ponent at this wavelength wasapproximately 4 per cent). As showninTable 6, glasseswererejected if TITs wasoutsidethe limts 1.000.15.The technique wasalsoapplied to the examnation of stock glasses.Thethickness required to give standard color was readily determned bymeasuring TIT. and referring to a calculated curve relating TIT. torelative thickness (absorbancy ratio). The neutral component of thestandard for Amber (Table 6) required no testing, sincesmall variationsin thickness did not noticeably affectthe colorof acombination.

COLOR COMPARATORSThe color comparators adopted for usewith the glass standards in

classifyingextracted honey for colorwere identical with those devisedfor maple sirup (5) and areillustrated in Fig. 4. The three lighter glassstandards aremounted behind alternate apertures 30mmsquare in onecomparator, and the three darker standards are mounted in a secondcomparator, Square bottles of 31.5mm internal thickness, filledwithdistilled water, areplaced in the compartments behind the glassstand- .ards toserveasblanksand toduplicatetheappearanceoffilledbottles ofextracted honeywhentheobserverlooksthrough thestandard apertures.A square bottle filledwith extracted honey to be classifiedis placed inoneof the compartments between adjacent standards. The comparatorisheld 12to 18inchesfromtheeyeand acolorcomparisonismadewithnatural orartificial daylight usedasasource.Threeturbid suspensionsdesignatedCloudy1,Cloudy2, andCloudy3areprovidedinsquarebottlesasaccessoriestoaidinclassifyingextractedhoneyhavingnoticeableturbidity. Thesearesuspensionsofdiatomaceousearth (Johns-Manville Hyflo Super-Cel) in concentrations of 100, 200,

FIG. 4.-Color comparators for extracted honey, showing the six glass color,standards mounted as windows, backed by three clear blanks and by the three'cloudy suspensions 1, 2, and 3 in square bottles; and two samples of honey to beclassified.


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1966] BRICE et al.: GLASSCOLOR STANDARDS FOR HONEY 935and 400 mg/l in distilled water. When a turbid honey is to be classified,the clear blanks are replaced by the cloudy suspensions, which may beswitched from compartment to compartment until a final comparison ismade between the sample and a glass standard (backed by a cloudy sus-pension) at about the same level of luminance. Tests with the polarizationphotometer indicated that superposing a cloudy suspension on a glassstandard does not perceptibly disturb achromaticity match, although thesuspensions are slightly selective in spectral transmittance.The average internal thickness of the square bottles is 31.5 mm with astandard deviation of about OA mm. They are not of good opticalquality, but are convenient, inexpensive, and adequate for routine colorclassification. Errors can occur only when the chromaticity of the honeyis near that of a standard. More precise classification, or refereeing adisputed color grade, can be done in the laboratory by using optical cellsof 31.5 mm internal thickness, the master glass color standards, and apolarization photometer with CIE Illuminant C.Features of the new color comparators contributing to more precisecolor classification of extract honey are: The relatively greater thicknessof sample viewed, resulting in a much wider spacing of standards on achromaticity scale; large square viewing apertures (30X30 mm) with arelatively narrow dividing line (9 mm) between standard and sampleapertures; and finally, use of color standards that are completely de-scribed in the CIE coordinate system, with established color tolerancesfor duplicate standards.As stated earlier in the paper, color classification of extracted honey isdone on the basis of chromaticity only; the glass color standards furnishboundary points for the color classes on a one-dimensional chromaticityscale.The glass standards became the official United States Department ofAgriculture color standards for extracted honey in 1951and wereadjustedto their present form in 1953. Complete grading sets are available com-mercially from the Phoenix Precision Instrument Company, Philadelphia,Pa. About 200 sets are now in use by the industry and by governmentinspection agencies.

SUMMARYPrevious official color standards for extracted honey weredefined in theDepartment's grade standards in terms of six scale readings on the PfundColor Grader. In order to provide a more convenient and economicalmethod of official classification for color on the basis of the U.S. standardsfor grades of extracted honey, six glass standards and simple color com-parators were developed. The glasses were closechromaticity matches for

caramel-glycerin solutions in 31.5 mm thickness, and were prepared togive the required scale readings in terms of the primary standard wedge


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936 ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS [Vol. 39, No.4of the Pfund Color Grader. The "standard" caramel-glycerin solutionswere shown to be spectrophotometricaUy similar to samples of clarifiedextracted honey, and were characterized in terms of several one-dimen-sional color scales in use in the sugar industry. Complete specificationsfor the glass color standards and the caramel-glycerin solutions werepresented in the CIE coordinate system.Color tolerances were established in NBS units of color difference, anda simple one-wavelength method of testing glasses was developed for theproduction of duplicate glasses.

ACKNOWLEDGMENTSThe project was carried out in cooperation with the Processed Products

Standardization and Inspection Branch of the Agricultural MarketingService. The suggestions and continued interest of F. L. Southerland andhis staff are gratefully acknowledged. The authors are indebted to HenryJ.Scherr for grinding and polishing glasses.REFERENCES

(1) SECHRIST,E. L., The Color Gradingof Honey, U.S. Department of Agriculture,Dept. Circ. 364, October 1925.(2) United States Grades, Color Standards, and Packing Requirements for Honey,U.S. Department of Agriculture, Circ. No. 24, December 1927 (revised August1933).(3) United States Standards for Grades of Extracted Honey, U.S. Department ofAgriculture, Agricultural Marketing Service, issued January 30, 1943 (re-issued December 15, 1945).(4) BRICE, B. A., TURNER, A., JR., SOUTHERLAND,F. L., and BOSTWICK,E. P.,The Canner, 110, No.6, 10 (1950). (Also AIC-260, Feb. 1950, EasternRegional Research Laboratory.)

(5) BRICE, B. A., and TURNER, A., JR., J. Opt. Soc. Am, 46, 293 (1956).(6) BRICE, B. A., TURNER, A., JR., WHITE, J. W., JR., SOUTHERLAND,F. L.,

FENN, L. S., and BOSTWICK,E. P., Beekeepers Magazine, 14, 7 (1951).(Also AIC-307 (May 1951), Eastern Regional Research Laboratory.)

(7) JUDD, D. B., Color in Business, Science, and Industry, John Wiley and Sons,New York, 1952.

(8) JUDD, D. B., J . Opt. Soc. Am, 23, 359 (1933).(9) DEITZ, V. R., PENNINGTON, N. L., and HOFFMAN, H. L., JR., J . ResearchNatl. Bur. Standards, 49, 365 (1952).(10) ANON., International Sugar J., 57, No. 680 (1955); Subject 13A, "Colour and

Turbidity of Sugar Products," pp. 278-285.(11) Report of Commttee on Spectrophotometry, This J ournal, 37, 54 (1954).(12) KEEGAN, H. J., and GIBSON, K. S., J . Opt. Soc. Am, 34, 770 (1944).(13) GIBSON, K. S., WALKER,G. K., and BROWN,M. E., J . Opt. Soc. Am, 24, 58

(1934).(14) PETERS, H. H., and PHELPS, F. P., Technol. Papers Bur. Standards, 21, 261(1927), No. 338.(15) WOLFROM,M. L., Editor, Advances in CarbohydrateChemstry, Vol. 9; LIGGETT,

R. W., and DEITZ, V. R., "Color and Turbidity of Sugar Products," pp. 247-284, 1954.

(16) PHILLIPS, E. F., J . Agr. Research, 45, 757 (1932).

Ir* ,It


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1956] BRICE et al.: GLASS COLOR S'ANDARDS FOR HONEY 937(17) HONIG, P., Editor, Principles of Sugar Technology, Elsevier Publishing Co.,

New York, 1953; GILLETT, T. R., Chapter 8, "Color and Colored Non-sugars."(18) GILLETT, T. R., MEADS, P. F., and HOLVEN, A. L., Anal. Chem, 21, 1228(1949).(19) ZERBAN, F. W., SATTLER, L., and MARTIN, J., tu, 23, 808 (1951).(20) ZERBAN, F. W., MARTIN, J ., ERB, C., and SATTLER, L., ibid., 24, 168 (1952).(21) MCGINNIS, R. A., A.S.T.M. Bull. No. eoi, 42 (Oct. 1954).(22) MACADAM,D. L., J.Opt. Soc. Am, 33,18 (1943).(23) BRICE, B. A., HALWER, M., and SPEISER, R., tu, 40, 768 (1950).

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White32 Glass Color Standards