268 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I Tristimulus colorimeters Angles of illumina- Instrument C.I.E. tion Pattern Price Notes illuminant I =Incident size category I V----Viewing Coloreye C I=diffuse 27ram M Normally includes Signature (small V=85 ø also 10 or 16 narrow sphere model) band spectral filters, and so functions also as an abridged spectrophotometer. Some directional effects which may be overcome using rotating accessory. Coloreye A,C. 1----diffuse 50ram N As above but Signature (large V=85 ø to relatively non- sphere model) 150ram directional. UV source available for L.S. model to enable measurements of fluorescence to be made. Colormaster A,C. I---- 45 ø 13m to L Marked directional Model V V----90 ø 45m effects which may be overcome by using rotating accessory. Elrepho A,C. I----diffuse 30m L Normally includes 7 V----90 ø spectral filters and I so functions as an I abridged spectro- photometer. With special xenon source can be used for fluorescent measure- ments. Relatively non-directional. Spectromat A,C. I • diffuse 10m to BI Direct print-out of FS-3A V=90 ø 40m X Y Z tristimulus values. Abridged spectrophotometer I (33 filters). Xenon t light source fitted as I standard. Relatively non- directional. The Color-Eye Signature is manufactured by Kollmorgen Inc. (I.D.L.), the Colormaster by Manufacturers Engineering Equipment Corporation, U.S.A., the Elrepho by Carl Zeiss, West Germany, and the Spectromat FS-3A by Pretema A.G. Sxvitzerland. (The price categories are: L about oe1,500, M about oe2,500, N over oe3,000.

INSTRUMENTAL COLOUR MEASUREMENT AND CONTROL 269 Table II Colour difference instruments Instrument Colour analysis display computer (C.A.D.C.) (Kollmorgen) Colerede (Kollmorgen) Hunter D•O5 M Colour difference meter (Hunter Lab., U.S.A.) Price category Notes Used in conjunction with a tristimulus colorimeter for the rapid analysis of the colour difference between a sample and control in terms of MacAdam units. Very stable, repeatability 0.2 units and designed to work on a 24 hr basis Continuous automatic colorimeter which gives a continuous display of colour difference between a standard and production material. Designed for use with continuous processes such as paper machines. Colour is measured directly in Hunter uniform colour space co-ordinates L, a, b, and colour difference may be expressed as AL, Aa, Ab. An important consideration in the choice of colorimeter for colour control work is its viewing geometry, i.e. the angie of illumination of the c,,,,,nmc,c, may sample. and the anglo of •ho measured r•O•*,•a l•,,,, A '"•' * • -I ................ ,•11 • •-•.u liblib. • either have diffuse or directional viewing conditions. In the former, the sample may be illuminated by a beam approximately normal to its surface and reflected light collected within an integrating sphere for measurement, or the sample may be illuminated by light from the wall of an integrating sphere and collected at a direction approximately normal to the surface of the sample. This type of instrument may be used for colour measurement of samples having both uniform and non-uniform surface structures and in the case of highly glossy samples provision is made to exclude light reflected in the specular direction (mirror reflection). All the instruments listed in Table 1 use these viewing conditions with the exception of the Colormaster V which has directional viewing conditions. It illuminates •he sample in a direction at 45 ø and measures light reflected in a normal direction. Reliable single measurements with this instrument are therefore restricted to samples with uniform surface structures since measurements would otherwise vary with the orientation of the pattern presented to the instrument. A sample