Colour subtractive

It is of particular interest that the dark grey colour of the pillar top is not obtained via a single pigment but by colour subtraction of a mixture of at least... 

Figure 2.1 (a) Additive colour mixing (b) subtractive colour mixing... 

Procedure. Steam is passed through the steam distillation apparatus for 20-30 min. Check the performance by pipetting 5 ml ammonium-N standard solution into the distillation unit, add 1 drop octan-2-ol, 6 ml magnesium hydroxide suspension and steam distil the released ammonia into 5 ml boric acid solution in a 100-ml conical flask. After approximately 40 ml distillate has been collected over a 5-min period, wash the tip of the condenser into the distillate, add 2-3 drops mixed indicator solution and titrate with 0.005 M H SO until the colour changes from green to purple. A blank distillation/titra-tion is carried out using 5 ml ammonia-free water and subtracted from the standard titre to give a result which should be 5.00 ml. 

Similarly pipette 5 ml of the soil extract into a plastic vending cup, followed by 5 ml sulphuric acid, 1.5 M. If the soil extract solution is highly coloured after addition of the acid, pipette a duplicate sample and add the 5 ml of sulphuric acid, 1.5 M. Add the other reagents, as detailed above, to the first sample, but only add the ammonium molybdate reagent to the duplicate. Measure the absorbance at 880 nm. For coloured extracts, subtract the absorbance of the duplicate without ascorbic acid, which will not develop the blue colour, from the absorbance of the sample extract with ascorbic acid. 

In colour photography the film is multilayer, each layer containing the chemicals required to produce one of the three additive or subtractive primaries. In practice, it is those processes which use the subtractive YMC primaries that dominate the market. However, even in these cases the additive process is used to record the blue, green and red components of light in three layers the yellow, magenta, cyan subtractive primaries being produced in subsequent processing. ... 

The ink jet printing of coloured images is a subtractive process and requires a YMC trichromat as in colour photography. Some of the properties required in the dyes are listed below. 

Interference between light waves of the same wavelength can be constructive or destructive, i.e. they can add to or subtract from each other, and this interaction is angle dependent. Therefore the colour observed is also dependent on the angle of illumination and on the angle from which the pigment film is observed. 

Subtractive colour mixing is used for dyes and pigments where the primary colours are red, yellow and blue. 

Figure 9.1 Typical screen layout of a databrowser (Micromass OpenLynx ) enabling overview and easy access to the data acquired in the analysis of samples from a 96-well plate. The screen shows (a) a representation of the 96-well plate with colour-coded samples (green is found, red is not found), (b) the peak hst for the selected well on the plate (position HI in this particular case), (c) a back-ground subtracted spectrum of the component selected in the peak hst, and (d) the smoothed total-ion chromatogram acquired for the selected sample. Reprinted with permission from . Chromatogr. A, 1000 (2003) 413. 2003, Elsevier Science B.V.

One of the simplest tristimulus colorimeters is the Lovibond Tintometer. The apparatus consists essentially of a viewing tube and light reflected from a standard white surface. One half of the field is illuminated by the light reflected by, or transmitted through, the specimen under examination. The other half is illuminated directly by a beam of standard light. Into the path of the latter beam coloured glass filters of the subtractive primaries are inserted and moved by mechanical means. 

The reproduction of colour in printing and photographic processes is by subtractive colour synthesis in which inks... 

The drawbacks inherent to signal subtraction can be circumvented by exploiting real-time subtraction, and this strategy is the basis of dualwavelength spectrophotometry (see 4.1.1.4). The beneficial influence of DWS in flow injection analysis was demonstrated using the dye approach where buffered coloured solutions mimicked the sample and sucrose was added as the Schlieren-generating species [28]. The Schlieren effect was almost quantitatively suppressed (Fig. 4.15 and Table 4.4). 

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