Adding colour

Spinels (AB2O4) (see Box 12.6) are an important class of oxide for the manufacture of brown and black pigments for ceramics. The three spinels FeCr204, ZnCr204 and 

ZnFe204 are structurally related, forming a family in which Fe + or Zn + ions occupy tetrahedral sites, while Cr + or Fe + ions are octahedrally sited. In nature, cation substitution occurs to produce, for example, black crystals of the mineral franklinite (Zn,Mn,Fe)(Fe,Mn)204 which has a variable composition. In the ceramics industry, spinels for use as pigments are prepared by heating together suitable metal oxides in appropriate stoichiometric ratios so as to control the cation substitution in a parent spinel lattice. In (Zn,Fe)(Fe,Cr)204, a range of brown shades can be obtained by varying the cation site compositions. For the commercial market, reproducibility of shade of colour is, of course, essential. 

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Annex II hsts foodstuffs that may not contain added colours unless these are expressly permitted by other annexes or they are present because of legitimate carry-over in an ingredient. The list includes unprocessed foods and processed foods that would not be expected to contain colours, also some processed foods hsted in subsequent annexes which may contain only a few colours. The list includes bottled waters, milk, cream, oils and fats, eggs and egg products, flour, bread, pasta, sugar, processed fruit and vegetables, extra jam, coffee and tea and preparations of these, salt, honey, certain spirits, and wine covered by Regulation (EEC) No. 822/87. 

Fig. 2.32. Chromatograms obtained at 420 and 500 nm for pure cochineal (a) and for cochineal adulterated by erythrosin (b), at a concentration of 0.35 X10-3 kg per kg cochineal, and by trans-fi-carotene (c) at a concentration of 6X10-3 kg per kg cochineal. Cochineal pigments dcH, dcIH, dcIV and dcVII, unknown pigments of D. coccus Costa ca, carminic acid fl, flavokermesic acid and ka, kermesic acid. marks the peak of the added colourant. Reprinted with permission from M. Gonzalez et al. [72].

Colourings. Most dilutable beverages are formulated with added colourings, although, depending on the fruit preparation used, many products... 

Colouring Matters.—When treated with an acid, a solution of the honey in water (1 3) remains unchanged in colour in absence of added colouring matters, but if the latter are present the liquid becomes more or less dark red. 

Tamarind concentrate shall be obtained by hot water extraction of clean tamarind pulp, with subsequent concentration under vacuum. The tamarind fruits shall be mature, sound, fresh and shall be free from insect and fungal attack or any other blemish which affects quality. There should not be any added colouring or flavouring agents. 

The requirements for a material to be effective as a UV protection finish include efficient absorption of UV radiation at 300-320 mn, quick transformation of the high UV energy into the vibration energy in the absorber molecules and then into heat energy in the surroundings without photodegradation. Further requirements are convenient application to textile fibres and lack of added colour for the neated fibre. Some typical chemical snuctures useful for UV protection are shown in Fig. 

Spray deposition can be monitored using water-sensitive paper or glossy white cards in conjunction with an added coloured dye. Alternatively, a fluorescent... 

Colourants should be added at the maximum consistency that allows for thorough mixing of the furnish and colourant to take place. Preferential dyeing of fibres can take place if dye and a limited portion of the fibre are kept in contact for any period of time. By adding colourants, particularly anionic direct dyes and pigments, at a lower consistency, the Yoshida and van der Waals forces are less effective and dyeing... 

AT-Bromosuccinimide was proposed as a titrant of ascorbic acid and the suggested method has been adapted by Evered to the determination of ascorbic acid in highly coloured solutions such as blackcurrant juices. The method has been tried by the writers but anomalous results have been obtained on certain samples where figures were considerably higher than those obtained by the official dichlorophenolindophenol method these anomalous results were confirmed in other laboratories on the same samples and are probably due to the presence of added colouring matter. 

Canned Fresh Garden Peas have sugar as their second largest ingredient and glucose at number four plus added colouring and flavouring. 

Tube Initial colour Physical slate of iron added Colour after 10 minutes... 

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