Color measurement and control

The sugar industry has always been in the forefront of chemical control. The most important areas of control include measurement of sugar content (done by polarization), pH control (because sugar is unstable at low or high pH, and more so when high temperatures prevail), color measurement, and control of vacuum pans (for good crystallization). 

See color measurement and control for a discussion on applying color quality standards (color evaluation, comparison, matching, and specification). However, a case of special interest is assoicated with the tendency for many initial colorless or white, transparent, or translucent polymers to develop undesirable yellowish color, with aging in particular. A standard method (ASTM D1925), based on the use of a recording spectrophotometer for transmittance and reflectance measurement, permits the determination of a yellowness index (YI). 

Hessner, M.J., Wang, X., Khan, S., Meyer, L., Schlicht, M., Tackjes, J., Datta, M.W, Jacob, H.J., and Ghosh, S., Use of a three-color cDNA microarray platform to measure and control support-bound probe for improved data quality and reproducibility. Nucleic Acid Res., 31(11), 1-9, 2003b. 

The precision and accuracy of instrumental color measurements and the associated color tolerance can provide a system of control that equals that of an experienced color matcher. But to achieve this performance, the product standard and production test specimens must be of the highest quality. As was pointed out, more than two decades ago, the weak link in instrumental color control is the specimen. The human visual system can scan a specimen marred by many inconsistencies and the human mind will ignore those features that are not relevant to the job at hand. A analog or digital colorimeter cannot ignore those defects. A spectrocolorimeter is a tool for the color matcher but it is not a hammer. It needs to be treated like the precision instrument it is. A mold-maker would never use his or her tools in a dirty... 

The measurement and control of color and gloss parameters is critical because of aesthetic reasons and provides an indirect measure to control process parameters. The impression gloss consists of several appearance phenomena - specular gloss, haze, DOI and surface smoothness. The evaluation of surface smoothness has major influence on the total appearance and is currently only evaluated visually. The presented new measurement technique correlates with the visual assessment of orange peel and objectively measures surface smoothness. The measurement results of the new orange peel instrument (long - and short-term waviness) were related to different process parameters, such as substrate roughness, in an actual case study. 

Post-consumer plastic color-measurement technology control is used in recycling of post-consumer plastics (PCPs). As the demand increased for consistent natural and other colors of particularly recycled PET and HDPE, the need for standardization and codification of color measurement based on analytical data continued to be critical. In the past the human eye was the only means of determining color quality. Samples... 

In looking back over 26 years of commercial experience It Is appropriate to comment on product quality. Significant improvements have been made compared with the commercial Delrin of 1960 in terms of melt stability, molecular weight distribution and control, the level and uniformity of physical properties and the color and colorability of natural color product. These product improvements were achieved by persistent chemical and engineering effort on the chemistry of the process, modernization of equipment, compounding technology and automated measurement and control systems. 

This brochure contains over 100 full-color pages of the latest state-of-the art products from the company s automation line including programmable logic controllers, smart relays, enclosures, process measurement and control devices, motion control sensors, human machine interface, pushbuttons, proximity sensors, relays and timers, and wire connections. Also included is a user-friendly index for easy product search, economical choices, popular models, and accessories. 

Durability. Grass-like surfaces intended for heavy-duty athletic use should have a service life of at least eight years, a common warranty period provided by suppHers. Lifetime is more or less proportional to the ultraviolet (uv) exposure (sunlight) and to the amount of face ribbon available for wear, but pile density and height also have an effect. Color is a factor generally uv absorption is highest with red fabrics and least with blue. In addition, different materials respond differendy to abrasive wear. These effects caimot be measured except in simulated field use and controlled laboratory experiments, which do not necessarily redect field conditions. 

Statistical quality control is used to first measure and then continuously improve product quality. For example, The Dow Chemical Company s average 1989 performance compared to the typical sales specification were purity, = 99.65 wt % color, APHA = 4 acid (as HCl) = 7.3 ppm and water = 26 ppm. Averages of properties were based on rail car and tank tmck shipment samples during 1989. 

In continuous dyeing there are many variables and the rapidity of the dyeing process requites many adjustments during the period in which several thousand meters of textile are dyed. Instmmental science has continued to advance rapidly so that continuous ranges are available which are entirely computer-controUed except for the makeup of the dye mix. These units feature computer control and closed-cincuit television and continuous color measurement techniques. 

Color Difference Evaluation. Shade evaluation is comparable in importance to relative strength evaluation for dyes. This is of interest to both dye manufacturer and dye user for purposes of quaUty control. Objective evaluation of color differences is desirable because of the well-known variabihty of observers. A considerable number of color difference formulas that intend to transform the visually nonuniform International Commission on Illumination (CIE) tristimulus color space into a visually uniform space have been proposed over the years. Although many of them have proven to be of considerable practical value (Hunter Lab formula, Friele-MacAdam-Chickering (FMC) formula, Adams-Nickerson formula, etc), none has been found to be satisfactorily accurate for small color difference evaluation. Correlation coefficients for the correlation between average visually determined color difference values and those based on measurement and calculation with a formula are typically of a magnitude of approximately 0.7 or below. In the interest of uniformity of international usage, the CIE has proposed two color difference formulas (CIELAB and CIELUV) one of which (CIELAB) is particularly suitable for appHcation on textiles (see Color). 

With the best observing conditions, it is possible for the trained observer to compete with photoelectric colorimeters for detection of small color differences in samples which can be observed simultaneously. However, the human observer cannot ordinarily make accurate color comparisons over a period of time if memory of sample color is involved. This factor and others, such as variability among observers and color blindness, make it important to control or eliminate the subjective factor in color grading. In this respect, objective methods, which make use of instruments such as spectrophotometers or carefully calibrated colorimeters with conditions of observation carefully standardized, provide the most reliable means of obtaining precise color measurements. 

All the analytical methods mentioned to separate, identify, and quantify chlorophylls and derivatives consume time, money, and samples. As alternatives, industries have been employing non-destructive methods for surface color measurements that are not only indirectly related to chlorophyll content, but may also estimate the pigments directly in tissues, leaving the sample intact and enabling serial analyses in a relatively short time. Eood color affects consumer acceptance and is an important criterion for quality control. Color vision is a complex phenomenon that depends on both the total content and number of pigments and also on absorption, reflectance and emission spectra of each compound present. 

Absorbance is measured at A s-max 420 mn of the bisulfite-treated sample and control sample. Consequently, color density is the sum of the absorbance at... 

There are several important points that need to be stressed. First, the estimation of discoloration in meat by measurement of percent metmyoglobin is useful in a relative sense only. Proper control samples (i.e., nontreated samples subjected to identical conditions, dilutions, and analyses, as treated samples) must be in place, and color measurement must occur in the same manner with both control and treated samples. Additionally, comparisons of values for percent metmyoglobin between different laboratories are only valid when investigators use the same measurement procedure. The use of three different formulas (i.e., from three different procedures) will yield different values for percent metmyoglobin. Again, it is the relative differences between treatments, or the changes over time, that become important, and... 

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