Colour variable pigments

Colour variable pigments in our Variocrom range are made of pi-large aluminium flakes which are covered by several layers of Si02 and Fe203, each a few hundred nanometers thick. This multi-layer plate-like structure produces an angle dependent, iridescent colour play. The Si02-layer with a... 

There are four main manufacturers of pearlescent or colour variable pigments with properties of the types discussed in this section, namely Merck, Engelhard, BASF and Flex Products. Some of the current ranges from these manufacturers are given in... 

Figure 5.20 Structure of colour variable pigments and possible combinations of layer materials.

Figure 5.21 Process for producing colour variable pigments by CVD.

Colour by Physics was the term used by Flex Products when they launched their Chromoflair range of colour variable pigments in 1996. 

Yolk colour plays a role in consumer acceptance, but the preferred colour varies in different countries. Yolk colour has no relation to nutrient content, flavour or freshness, but is often enhanced in conventional production systems by addition of synthetic pigments to the animal feed. In organic production, synthetic yolk pigments are prohibited and this normally results in paler yolks, but may also lead to greater variability in yolk colour intensity. In many European countries paler yolk colour is perceived by consumers as being associated with less natural production systems, an issue that clearly needs to be addressed by improved consumer information. 

The effects of the changes in the preparation methods were assessed by measuring the colour of the pigments in draw-downs and the particle size distributions of the powders. It was found that changes in all the listed variables could produce changes of several NBS... 

Figure 5.12 Variable colour pigments formed by polymerisation of chiral nematic liquid crystals.

Ancient artists knew of two other intensely blue pigments and these were made from the minerals azurite and lapis lazuli. Azurite is a variant of basic copper carbonate. Lapis lazuli is more complex and is a silicate rock with variable amounts of aluminium, sodium, calcium, and sulfur and was known as ultramarine. This mineral is found alongside marble and is produced when rock becomes heated under great pressure. It was mined only at Badakshan, Afghanistan,8 1 and such was its rarity in Europe that it was worth its weight in gold. It was imported via Venice and many believed it was being secretly manufactured in that city. Such was the beauty and depth of its colour that... 

Commercial Preparation and Uses of Prussian Blue.—Prussian blue was discovered accidentally in 1704 by Diesbach,4 and is highly valued as a pigment on account of its remarkable intensity of colour. It was manufactured in Great Britain in 1770, and sold at 2 guineas per lb. One pound of Prussian blue will perceptibly tinge some 600 lbs. of white lead. The pigment is sometimes prepared commercially by the direct method of adding a ferric salt to a solution of potassium ferrocyanide but it is more usual to adopt an indirect method, namely to add a ferrous salt to potassium ferrocyanide and subsequently to oxidise the white precipitated mass of ferrous potassium ferrocyanide.5 Chemically it consists of a variable mixture of some or all of the Prussian blues already described. 

This chapter has attempted to present the basics of colour measurement as applied to foods. It is important to realise that the wide variability in the nature of foods and food products, from both their structure and pigmentation, may limit any colour measurement technique applicable only to that particular food. This is because the numeracy of the data is unlikely to match the visual experience of equivalent reference atlas colours. In some cases this discrepancy may be large and has to be recognised as an intrinsic property of the food. These differences may arise from the difference of the visual experience of the product when viewed under normal lighting conditions as opposed to the limitations of its optical properties when presented to the particular colour-measuring instrument. This is... 

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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