GENERAL ELECTRIC - ACS Publications - American Chemical Society

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HOW G.E.'S RECORDING SPECTROPHOTOMETER HELPS YOU

Set Color Tolerances for Production Runs PROBLEM 1

factors which describe a color in terms of accepted color experience—hue, vividness a n d lightness.

Suppose you are making a grey material in production lots t o m a t c h a customer's sample. You do not wish t o deviate more The numerical values are first obtained on t h a n a selected a m o u n t from t h e pre­ t h e customer's sample. We use t h e values determined standard sample as devia­ for hue and vividness as t h e origin for a tions or rejects can be very costly. You graph. (Lightness is indicated in paren­ can measure t h e color of t h e customer's theses.) All samples are then plotted sample and of lots which you and t h e b y their difference from t h e standard customer agree are acceptable matches. sample. T h e ellipse represents a visually I n addition, you can measure all produc­ equal step in chromaticity, therefore, all values which plot within t h e ellipse are tion runs and chart these values t o be acceptable color matches providing t h e sure t h e color produced is within agreedlightness factor is not too great. This upon tolerance limits. simple representation of color is helping manufacturers in such industries as tex­ HERE'S HOW tiles, printing inks, dyestuffs, plastics and An automatic computer, called t h e Tri- paper substantially decrease manufactur­ stimulus Integrator, can be used with t h e ing costs and produce products of better, General Electric Recording Spectropho­ more consistent quality. This technique tometer. This device gives you, in only also helps t o reduce disagreements over SAMPLES OF PRODUCTION can be run quick­ ly and charted immediately to give indi­ 54 seconds, numerical values for three "acceptable m a t c h e s . " cation of variance from the standard.

Know How Color Changes from Lot to Lot PROBLEM 2 Suppose your c h a r t shows t h a t consecu­ tive batches of your daily production are getting further and further from t h e standard. Analysis of t h e chart will tell you how your process is varying and will suggest corrective measures which m a y be t a k e n t o bring your process back under control.

Sample A is acceptable although there is a slight shift to the green shade. Light­ ness is excellent (see zero in parentheses). Sample Β is unacceptable. T h e shade is on the borderline of excellence—slightly yellow b u t it is too light (4.3).

tometer or t h e Tristimulus Integrator, call your G-E A p p a r a t u s Sales Office or write Section 585-41, General Electric Company, Schenectady 5, Ν . Υ . T o get t h e latest news on color measurement, ask to be added t o our mailing list for t h e Spectrophotometry Digest.

HERE'S HOW T h e ellipse a n d c h a r t are d r a w n with relation to the natural arrangement of colors. For example, when a shade is run­ ning redder t h a n t h e s t a n d a r d sample, it will plot in t h e lower right-hand corner of AUTOMATIC COMPUTER gives numerical t h e chart. Lightness of colors is charted values. and t h e value is shown in parentheses on Sample C is unacceptable, the shade is t h e chart. W i t h this known information good b u t t h e sample is too light (3.6). you can quickly analyze your process and Sample D is unacceptable, shade is good see if more colorant needs t o be added or b u t sample is too light (3.2). t o see if t h e color mixture needs adjust­ Sample Ε is unacceptable. I t is too dark ment. ( — 10). T h e shade is within t h e accept­ Experience with this instrument will help able range b u t note the marked shift predict changes in color on similar jobs to t h e blue. and help you to establish controls for Sample F is unacceptable. Lightness is your color processes. OK b u t t h e shade is outside of the ellipse. FOR MORE INFORMATION about the On t h e chart, points falling within t h e dotted line are excellent color matches. General Electric Recording SpectrophoThose points inside t h e solid line are n o t quite so good. Points outside t h e solid line are n o t good color matches. For example :

GENERAL

ELECTRIC

For further information, circle numbers 8A-1, 8 A-2, 8 A-3 on Readers' Service Card, page 73 A 8 A

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ANALYTICAL CHEMISTRY