Standards, colour

For work of the highest precision a comparison solution or colour standard may be prepared for detecting the equivalence point. For 0.05 M solutions, this is made by adding 5 drops of methyl red to a solution containing 1.0 g of sodium chloride and 2.2 g of boric acid in 500 mL of water the solution must be boiled to remove any carbon dioxide which may be present in the water. It is assumed that 20 mL of wash water are used in the titration. 

Column chromatography see Chromatography Columns in gas chromatography, 238 in liquid chromatography, 223 Combustion flames 784 Common ion effect 26 quantitative effects of, 35 Comparators permanent colour standards,... 

Quantitive analysis was based on the standard addition method colourant standards were added to each food sample in the range 1 to 5 pg/ml. Values are the mean of nine measurements. bValues are the mean of nine measurements. 

Color is important in all forms of potato products, boiled, baked, fried, and chipped. Where a limited number of broad classifications are used, as in some commercial processing situations, use is made of visual reference charts showing a limited range of colors. Such charts are available for French fiies (Munsell USDA Frozen French Fry Standard, X-Rite Right On Colour) and for potato chips (Colour Standards Reference Chart for Potato Chips, Snack Food Association). 

Many modifications of the apparatus and method have been recommended.1 Discs of paper may be fixed across the mouth of the tube B in various ways and the stain, thus localised, is uniform in colour and sharp in outline and therefore more readily compared with standards.2 Mercuric bromide papers are satisfactory in use,3 but should be freshly prepared the stains may be developed in aqueous potassium or cadmium iodide and compared with a colour standard.4... 

Liquid extracts such as infusions will often, over time, produce a fine sediment. There may be a statement to this effect in the specification and on the container label. If the product for which the extract is destined is a cloudy drink or opaque like a fruit juice, then the container can be shaken each time to re-disperse the sediment before weighing out. If it is essential for the extract to be clear, then it must be carefully decanted when weighing out for a production batch. Extracts in storage will often change colour over time. Thus, specifying a colour parameter without a time factor can lead to the situation where a customer s QC accepts the extract on delivery, as it meets colour standards at the time, but rejects it on retesting later after it has spent some time in the raw materials store -particularly if the drum has been opened and is part used. 

With the former instrument, comparison is made with a double disc of yellow glass of definite depth of colour (standard colour), and when a 100 mm. layer of a liquid corresponds in colour with the standard, the colour of the liquid is taken as 1 thus, the colour of any liquid is obtained by dividing 100 by the depth in mm. of the layer necessary to equal the standard colour. The value obtained is then referred to 100 of pure sugar, allowance being made for the sugar content of the juice and for the extent to which it is diluted for the determination of the colour. 

In semi-automatic moulding the operator may inspect each unit for features including colour, dispersion and uniformity of colour, standard and uniformity of gloss or mattness, and the presence or otherwise of defects like silver streaks or stringing. However, it is preferable if assessments can be made in numerical terms, expressed in units that may be compared quantitatively and subjected easily to statistical treatment and analysis. It is often convenient in the course of... 

J. F. Verrill and F. Malkin, Thermochromic Behavior of the Ceramic Colour Standard, paper presented at the AIC Silver Jubilee Meeting, Princeton, NJ, June 23-24,1992. 

The preparation of reference standards in this procedure is a tedious task and may require considerable time. Time can be saved by applying what is called a permanent colour standard method, which requires a special device, the so-called comparator. The Lovibond comparator, shown on Fig. 1.8 employs nine permanent glass colour standards, fitted on a revolving disc. The device is fitted... 

The Munsell chart and Ostwald s system are not all that might be desired because their construction and use are not free from subjective elements they have other limitations such as lack of permanency of the colour standards. In 1931 the Commission Internationale de I Eclairage, usually referred to as the C.I.E., recommended what is known as the C.I.E.. system for numerical specification of colour. The foundation on which the method was based was the colour triangle illustrated in Fig. 26.9. It is assumed that the corners of an equilateral triangle are illuminated by the... 

Where assessments take place on a production line, good consistent conditions for viewing the sample or matching to a memorised or formal colour standard need to be made available. Market researchers often find themselves in conditions unsuitable for the making of reliable appearance assessments. A specification of the environment of the test, including types of illumination and colour of the test surrounds, should be noted in the final report. This will make it easier for the occurrence of colour metamerism problems to be minimised. If the consumer s views of product colour and appearance are important to the project, standard lighting and viewing conditions should be provided. 

The ability to perform precise, calibrated digital measurements is a welcome breakthrough for the science and technology of food appearance. As well as a new future for the measurement of appearance properties of three-dimensional materials it will be of great benefit for sensory assessment. Potential benefits include the development of on-screen panelhng and panel manipulation, communication and archiving. Another benefit will be the constraction of improved colour standards for panel use (see Chapter 14). 

Colour standards provide the references against which the colours of materials can be instramentally compared. They fall into two classes, primary standards and secondary standards. Primary standards are pressed powder tablets of fresh MgO, BaS04 or halon G-80 (pressed tetrafluoroethylene resin manufactured by the Allied Chemical Corporation) maintained by governmental standards agencies such as the National Bureau of Standards in Washington DC, USA or the National Physical Laboratory in Middlesex, England. These white standards are measured against a theoretical perfect white diffuser by means of an auxiliary sphere to derive an absolute reflectance value. Unfortunately, at the moment there is not a complete consensus between the various standards institutes on the perfect white diffuser values. 

Before a standard is used to calibrate an instrament, the irrstrament should be thoroughly warmed up and stabilised. Colour standards should be placed under... 

Kent and Smith (1987) reported the results of an inter-laboratoiy study on measmement of colom standards. They came to the obvious and important conclusion that in order to transfer and compare colour data from one laboratory to another, which is certainly necessary when colour is being used as a buying criterion, the measuring system and the colour standard have to be carefully defined. Most instrument manufacturers will provide details of best practice with respect to how the instrument and its standards should be maintained. 

A file of reference specimens of current printed packaging materials should be maintained. This should include a colour standard. 

FAC, Fat Analysis Committee of the American Oil Chemists Society colour standards, range 1- 5 (45 darkest). 

In the case of alpha-olefins, alcohols and alcohol ethoxylates high levels of decomposition products can also be present, notably high levels of 1,4-dioxane (0.5 - 1.0%) when alcohol ethers are sulphated and the residue remains in its acid form for long periods (hours). Residues from a plant running exclusively on alkylbenzene can be blended with the main production stream at a low level to meet sulphonic acid colour standards. 

Clarke, F. J. J., and Malkin, F. (1981) Development of a new series of ceramic colour standards. J. Soc. Dyers Colourists 97, 503. Description of current BCRA Series II color tiles supplied by NPL. 

Compton, J. A. (1984)l The thermochromic properties of the ceramic colour standards. Color Res. Appl. 9,15. Evaluation of thermochromism of BCRA series I tiles. Theory and praake also applkable to all other existing color standards to some degree. 

Fillinger, L., Lukacs, G., and Endor, G. (1978). Thermochromism of color standards. Hun. Sci. Instr. 44, 25 Fairchild, M. D., and Grum, F. (1985). The thermochromic properties of ceramic reference tiles. Appl. Optics 24, 3432 and Verrill, J. F., Knee, P. C., and O HaDoran, J. (1995). A study of the uniformity and thermochromism of surface colour standards. Abstract of paper presented at C.I.E. International Meeting, Berlin. Recent studies erf surface uniformity and thermochromism of currently used color standards [translucent blurring effect). 

Product range Narrow few colours, standard Wide many colours, choice... 

---