Red Lake Pigment

USE Dyeing red manuf of a red lake pigment. With alkalies = purplish-red with acids = yellow. 

As identification of the exact dyestuff in red lake pigments is difficult there has therefore been httle confirmed analysis on works of art. Kirby and White have however, examined a broad range of paintings in the National Gallery, London from 1400 to 1900. Cochineal is first foimd on a painting hy Gerard David of 1510. Its use thereafter becomes increasingly more commonplace. 

Kirby White (1996) Kirby, J. White, R. The identification of red lake pigment dyestuffs and a discussion of their use National Gallery Technical Bulletin 17 (1996) 56-80 Kirby (1977) Kirby, J. Two panels by the Master of St Giles. Materials, paint structure and techniques National Gallery Technical Bulletin 1 (1977) 49-56... 

The FD C certified colors are all water-soluble dyes, but can be transformed into insoluble pigments known as lakes by precipitating the dyes with alurninum, calcium, or magnesium salts on a substrate of aluminum hydroxide. The lakes are useful in appHcations that require color whereas in dry form, such as cake mixes, or where water may be present and bleeding is a problem, such as food packaging. FD C Red Lake No. 3 was deHsted in Febmary... 

The hue of a red azo pigment lake carrying sulfonic acid functions is determined to a considerable extent by the metal ion. In the series Na->-Ba->Sr->Ca->Mn the shift of hue from yellowish to bluish red increases in the order in which they are listed. The complex correlation between chemical constitution and color in pigment molecules poses a quantum mechanical challenge. This is complicated by interactions within the crystal lattice and by the contribution of intermolecular and... 

Red azo pigment lakes may be classified according to the coupling component. There are four industrially important groups. Pigments are based on the following coupling components ... 

In contrast to red azo pigment lakes, which have stimulated considerable technical interest, the corresponding yellow pigments are much less important (Sec. 2.3.1.2 2.3.4.1 Table 13). 

Lithol Red was followed by Lake Red C pigments, which were discovered by Meister Lucius Brilning, now Hoechst AG, in 1902. 

Both the barium lake P.R.49 1 and the calcium lake P.R.49 2 resemble Lake Red C pigments (P.R.53 1) in terms of fastness to organic solvents, to alkali and acid, and to fastness in application. However, P.R.49 grades are much less heat stable, which narrows their applicability in plastics. Areas of application, especially in the USA, include elastomers, to a lesser extent also inexpensive industrial paints, air drying and nitro paints. Their main market, however, is in printing inks. 

P.R.68 is supplied as a calcium salt. It produces a yellowish red shade, referred to as scarlet, which at equal depth of shade is slightly bluer than P.R.53 1, a member of the same class of pigments. P.R.68 has gained considerably less commercial recognition than the widely used Lake Red C pigments. 

P.R.58 4 is primarily used in general industrial paints, where its full shade and related shades are of interest. This is also true for other manganese pigment lakes. In full shade, P.R.58 4 affords deep carmine shades, but white reductions provide only very dull, bluish shades of red. The pigment is fast to organic solvents and... 

The aluminum lake is registered throughout the EC as E 132, in the USA as FD C Blue 2 as a colorant for foodstuffs and pharmaceuticals, provided certain purity conditions are met. Its shade is a bluish red. The pigment is somewhat sensitive to chemicals and to overcoating as well as to light. It is a tinctorially weak product. 

---