Colour system

Note. (1) More rapid clarification of the nitrobenzene extract is obtained if the beakers contain about five pellets of sodium hydroxide. The latter is, however, a source of instability of the colour system and its use is, therefore, not recommended. 

FIGURE 2.22 The three-dimensional CIELAB colour system. Left /zab (hue) describing the tonality of the color, where 0° corresponds to red, 90° corresponds to yellow, 180° corresponds to green, and 270° (or —90°) corresponds to blue, C represents the chroma (or saturation), where 0 is a gray tone, while 100 is a pure hue. Right the lightness (L ) goes from black (0) to white (100). 

The diazotype process is an example of a non-silver system with wide commercial application. In general, it is used in areas which require a monochrome or neutral high contrast image rather than a full colour system. For this reason, the image hue is not as critical, except for aesthetic reasons, as in the three-colour silver processes. Diazotype materials are primarily used in making direct reproductions of written, typed or drawn materials, particularly in the drafting, engineering and architectural professions. 

The different instruments (Hunter, Gardner, Instrumental Colour Systems, etc.) process absorbance and reflectance data in slightly different ways, which means that the values obtained can differ slightly from one instrument manufacturer to another. Therefore, a product s defined colour has to be qualified with a statement indicating the instrument used. Notwithstanding this limitation, it is not uncommon to find a tristimulus colour meter in a manufacturer s quality assurance laboratory so that routine quantitative assessment of a product s colour can be made. This is particularly tine for tomato-based products, whose nature makes conventional spectrophotometric assessment meaningless. 

Both spotted (cDNA and oligo) and on-chip synthesized (oligo) arrays are available. As an example this chapter will describe only the procedure for a two-colour system using an oligo spotted array (MWG Biotech AG). 

Brighton, 20th-22nd April 1999, p.388-97 PERFORMANCE OF POLYMERIC CARRIER BASED COLOURANT SYSTEMS IN RIGID PVC EXTRUSION Smith N Matthey J... 

Figure 2, continued, artistic translation of sequence into colour, sequence visualization according to the "iCene-Visions PerZan" colour system (http //www.perzan.de). Each codon is translated into a defined RCB-value. To increase visual harmony in the two images, the width of each bar is coupled to the lightness of its color, the lighter the color, the wider the bar. 

The illustrations reproduced by courtesy of Tintometer Ltd, Salisbury, were taken from The C.I.E. International Colour System Explained, by G.. Chamberlin. 

Despite the many possibilities of deviation from Beer s law, in the absorbance range of practical interest for analytical purposes, colour systems not conforming to Beer s law are fairly rare. 

In definite coloured systems the concentrations of reference solutions are selected with a view to obtaining maximum precision of the measurements. Particular attention is required in the preparation of standard solutions. In cases where temperature variations may influence the absorbance measurements, thermostating of the system is required. 

Most of the colour systems, used as a basis of spectrophotometric methods are formed as a result of complexing reactions. The most important spectrophotometric reagents are presented in Chapter 4. 

Colour systems suitable for use in the spectrophotometric method may also be formed in redox reactions. Some examples of such reactions are the oxidation of Mn(II) to Mn04" or Cr(III) to Cr04, oxidation of dimethylnaphthidine with vanadium(V) or chromium(VI), oxidation of o-tolidine with cerium(lV) or with chlorine. Examples of oxidation reactions are also the iodide methods, in which iodide ions are oxidized with bromine to give iodate ions which, in turn, react with the excess of iodide anions to form free iodine (see Chapter 25). A colour effect of reduction also occurs, for example, in determinations of Se and Te in the form of coloured sols produced in the reduction of Se(lV) or Te(IV) to their elementary forms. 

In some methods the colour system is a product of a synthesis reaction. Examples of such methods are formation of an indophenol dye in a method for determination of ammonia, the synthesis of azo dyes in the determination of nitrite, the formation of Methylene Blue in the determination of sulphur, the pararosaniline method for determination of sulphite, and the benzidine-pyridine method for determination of cyanide. 

The development of a new spectrophotometric method is usually preceded by studies of the colour system (complex composition and stability), which is the basis of the method. Fundamental physicochemical studies of the colour complexes existing in the solution enable one to establish the optimum parameters of the method [74-76]. The composition of the complex (molar ratio of metal to ligand) in the solution is determined by Job s continuous variation method, the Bent and French method of equilibrium shift, the method of mole ratio proposed by Yoe and Jones, and the method based on the ratio of slopes and isosbestic points. Studies of complex compounds in solutions are described in many works, especially [77-80]. 

The indirect absorptivity s (calculated as the decrease of absorbance of the Fe(III)-sulphosalicylate complex at 500 nm owing to the presence of fluoride) is 2T0 (a = 0.01). The colour system does not obey Beer s law. 

The Zr-ECR method has been applied for determination of fluoride in water [38], air [84], rocks and minerals [85-87], iron ore and apatite [15], and various reagents [39]. Various above-mentioned coloured systems Zr-organic reagent were used for determining fluoride in bones [49], waters [16], silicate rocks [47], phosphates [44], and uranium oxides [50]. 

It was not the first time that a prominent artist had made suggestions about camouflage techniques. Back in 1899, the American painter George DeForest Brush, who was known for his studies of protective coloration in nature, propounded a camouflage scheme that was intended to reduce the undesirable visibility levels that resulted from the standard United States Navy colour systems of that time. It is interesting to note that from November 1913 the British Fress had been advocating the adoption, by the Admiralty, of the Brush low visibility painting method for British ships too, albeit without success. 

For his low visibility colouring system. Mackay undertook the spectrum analysis of the light radititing from the sea w ith a view to synthesising these same colours on ships sides... 

It had been intended by the US Navy that both the Wakefield and Mount Vernon should be painted in a different, distinctive colour system — Measure 32 in design 1T. Measure 32, which was desiftned primarily as an antisubmarine... 

The Base Repair Ship Artifex iex-Aurania) in a distinctive camouflage colour system, probably a variant of the Admiralty Intermediate Disruptive Pattern. Imperial War Museum)... 

May be printed on flat sheet or from reels. May use either a four colour process system (cyan, magenta, yellow and black), or a multi-colour system. As indicated above, almost any printing process can be (and is) used. The most common methods of printing today are all sheet fed, mainly using letterpress and offset litho. 

As mentioned previously, the now routine integration of a pc means that the data collected from either a colorimeter or spectrophotometer can be transformed to XYZ, CIELAB, HunterLab or other colour system as specified by the user and provided by the software. The initial step from instmment response to XYZ requires the definition of standard observer functions. 

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