PIGMENTS, LAKES AND DYESTUFFS IN COSMETICS Fig. 6. Ultramarine blue. This is not Fig. 7. Phthalocyanine blue. The very one of the finest pigments but it provides fine particles characteristic of this blue brilliant clear blue colours. pigment provide high colour strength- X 5,500 only small amounts are needed in admix- ture xvith whites to give distinctive blue shades. X 20,000 Figures 8 and 9 illustrate Hansa Yellow and Lithol Red, two widely used organic pigments. Due note should Mso be given to the large variation in the pa?tic size as shown in Figs. 8 and 9. Both pigments will aggregate .... [3' •---"• •'"' '• • •2•' • • ] -•- • • • ,.•_ '•- ' .--- ',: .•2 :. ,-' - I TM ,•:• , *. - Fig. 8. Hansa Yellow. This pigment has high colour strength but its particles are quite different from those of phthalo- cyanine blue. X 5,500 Fig. 9. Lithol Toner (Red). This pigment has high colour strength, the crystalline particles being so thin as to make them appear transparent even in the electron beam, which has very limited penetrating powers. Very few pigments do not appear opaque in electron micrographs. x 5,500

10 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS considerably on filter pressing in the wet and subsequent drying these aggregates will not necessarily be broken down by subsequent grinding. The effect of the manufacturing process is well illustrated by Figs. 10-15, illustrating the growth of yellow hydrated iron oxide during processing. Fig. 10. The tiny particles first precipi- tated are too small and transparent for pigment use. The material appears bro•vn in colour. X 11 Fig. 11. The particles grow fairly rapidly in the precipitation vessel. After about half the normal period allowed the par- ticles have grown to the size shown. The colour is no•v much lighter. X 11,000 Fig. 12. After three-quarters of the nor- real period the particles have grown still further. The material is now yellow. X 11,000 Fig. 13. After the full ageing period the particles have reached the size shown. The colour is now a clean yellow and the material has suitable pigmentary pro- perties. X 11,0•0