174 



I'ii.MI.VfS 



ini|ini<lont to excise any kind (if artistic work in 

 i-.il.nn-. to direct sunlight in even, it woulil seem, to 

 ilir light of elect lie urc lamp-. Tin- following 

 refers I" tin- ilurnliility of pigments employed 

 in oil painting. \vl. ii continuously exposed to 

 fairly strong daylight. Aiming lilur colours, ultra- 

 marine, both real anil artificial, is permanent; 

 while 1'russian blue i* liable to some change, and 

 indigo is fugitive. Aiming nil colours, vennilion 

 anil tin- red ix-hres are perfectly ilnralile : while 



ili .i.l. I. -i reds ami purples can hardly be so 



thoroughly relic. I II|H>II, and the carmine and 

 crini!M>n lakes, frnm cochineal, quickly give way. 

 Among thf yellows, raw sienna, yellow ochre, as 

 well as tlie cadmium mid Naples yellows, are i|iiite 

 stalile ; while Indian, chrome, and lemon yellows, 

 and also aiireolin, although less HO, are yet fairly 

 durable, lint gamlMige ami yellow lake are not. 

 Among greens, oxi.le of chromium undergoes no 

 change, terre verte is practically permanent, and 

 HO also is emerald green, lint it is lilackened by 

 contact with cadmium yellow. Among lirowns, 

 Imriit sienna, raw and burnt iimlier. oappaatl 

 brown, mid ( 'aledonian brown do not at all fade; 

 lint hardly as much can lie said of madder lirown, 

 Cologne "earth, and Vandyke lirown, although 

 these are fairly durable. Asphaltum or bitumen 

 has a tendency to move on the canvas unless v.-i \ 

 carefully prepared, and its rich brown colour is not 

 altogether permanent. Lampblack, ivory black, 

 and charcoal black are quite durable, so also are 

 Hake white, zinc white, and baryta white. It is 



generally the case that a colour produced by a 

 mixture of permanent pigments is also permanent. 

 and it may be added here that Hake white (white 



lead ), so much used to mix with other colours for 

 light tints, is liable to discolour when exposed to 

 sulphuretted hydrogen (an occasional impurity in 

 coal gas), and this colour has also a tendency to 

 tarnish when kept in the dark. 



The above remarks on colours made up with oil 

 apply equally to water-colour pigments, with a few 

 exceptions. These are vermilion, especially if arti- 

 ficial, Naples yellow, chrome yellow, and madder 

 brown, the permanency of which cannot be relied 

 upon in \Vater-coluurs, under which head some 

 further remarks on this subject will lie found. 



Fuller information about the pigments named 

 above, ax well as others, will be found under the 

 heads A.SPH ALT, Ml.ACK, Bt.fK, (iHKKN I'KiMKNTS, 

 I.\KKK, OCHKKS, I'ritl'LKCol.llI Its. It I.I i ( '111.111 I!S, 



and VKI. i.ow I'].. MI vis. The oils ami varnishes 

 usi-.l n~ media for pigments, as well as the nature 

 of the prepared canvas or paper used for painting 

 IIJHIII, have all a liearing on the preservation of the 

 colours of a picture. See the ('ncmistry <*t 1'nintx 

 IIIK! l',,nil,H<i, by A. H. Church (1890). The 

 history of the introduction of the principal pig 

 incuts is given at I'AIXTINIJ, Vol. VII. p. 7<>'_'. 



1'iuiiiriils of Animals. That animals are 

 often brightly coloured is evident. Some of the 

 simplest, such as many Ka.liolaiians, are brilliant ; 

 sponges are often suffused with pigment ; sea- 

 aiiemoiies and corals are justly rompan^l to 

 Mowers ; many marine worms have an iridescent 

 sin-en ; the Kchinoderms are almost always bright ; 

 many crustaceans have a jewel-like 'rndiain ' : 

 myriads of insects are lustrous; the sliells of 

 molluscs are rich in beauty: the fishes gleam in 

 silver and gold and many hues: even the am- 

 phibians are sometimes gaily pigmcnted ; M 



lizards and snakes seem like Hashes of colour; 

 biids are often brilliantly decorated ; and mammals 

 have a siilxliicd but often lich eoloiiiing in their 

 fur. Hut all the colonm of animals are not due to 

 pigment--, for air-spaces in hairs and feathers make 

 these structures white ; crystals of guanin or lime 

 often produce a silvery glimmer; st rial ion and 



other physical peculiarities of the surface caiue 

 iridescence. 



The mott important 1'igmeuti. () Pigments 

 called lipochromcs are among the commonest, occur- 

 ring iii the skin of crustaceans, molluscs, h- 

 anu birds, in yolk of egg, in the vascular Huid of 

 invertebrates, and also in Dowers. Carotin, Int. 'in. 

 tetronery thiin, yellowish chloiophancs, and n.-v 

 rhodopliaiies are representative examples. The 

 reddish pigment conspicuous on many crustaceans 

 is probably a rhodophanc, and into ilii- or analo 

 gous lipiM'iiromes the bluish and greenish pigments 

 of some lobsters and crabs seem to lie converted 

 when the animals are boiled or preserved in 

 alcohol or treated with acids, (h) Melanoid and 

 lipochromoid pigments, usually of a dark colour, 

 sometimes derivable from () or from the sub- 

 stances which give rise to (), occur, for instance, 

 in Corgonid corals, shells of molluscs, the ink 

 of Sepia, the eyes of vertebrates, and in tumours, 

 (c) I ranidin pigments of a yellow colour, be- 

 coming brown or dark-violet in association with 

 ferments, occur in Tunicate.-. ( ;a-tiupo.ls. insect-. 

 and sponges, (it) Haemoglobin and its deriva- 

 tive*, of pre-eminent importance in c lection 



with respiration, are of wide occurrence. Hemo- 

 globin itself, the red pigment of the blood which 

 enters easily into a IIKISC union with oxygen. 

 is present in all vertebrates except Tunicates, 

 Amphioxii.s, and two or three (perhaps anu-mic) 

 fishes. Among invertebrates it is known in some 

 molluscs, crustaceans, and worms,' in the larva of 

 the dipterous insect Chironomus, and in a few 

 Echinouerms. It is not known to occur in any 

 coilenterate, sponge, protozoon, or plant. Among 

 the important denvate* of haemoglobin are h:emato- 

 porphyrin in the oviduct of birds, giving some of 

 the colour to the egg shells, bilirubin in the bile, 

 and biliverdin, another bile pigment, which also 

 occurs in the shells of some snails. As respiratory 

 pigments ought also to be reckoned the Ineiiio- 

 cyanin in the vascular Huid of molluscs and Arthro- 

 pods, various violet and purple lloiidine pigments 

 from sponges and from the I'oly/oon Itiigula, 

 and, according to Sin by, the aphidein of aphides. 

 (e) Chlorophyll, the almost constant colouring 

 matter of plants, apparently consisting of a mixture 

 of two pigments (chlorophyll green and chloro- 

 phyll-yellow), perhaps occurs in a few animals, 

 green infusorians, the fresh water sponge, the gii-cn 

 hydra. It is not quite certain, however, that the 

 green pigment of these animals is identical with 

 that of plant green : it may lie a closely analogous 

 substance. Chlorophyll-yellow is a lipochiome 

 and occurs in many animals. (/') Indigo pigments 

 are said to occur in the urine of mammals, and in 

 the purple secretion of the whelk I'urpnra. The 

 secretion of Murex, which turns violet in the light, 

 has not been siiHiciently investigated. 



l'lii/!iiiilii<i;i nf /'ii/iiifnlx. Within recent yeais 

 many of the pigments of animals haye been 

 analysed, and some facts about their relationships 

 have been discovered. Hut in regard to the con- 

 ditions of their formation, and the purposes which 

 they may s.'ivc within the body, comparatively 

 little is known. As the soil may influence the 

 colouring of Dowers, so the food given to birds 

 may afl'eei the Inightin'-- of their plumage. There 

 are several facts of a similar nature, (old seems 

 to lie one of the con. lit jons which induce a winter 

 change of colouring in a few birds and mammals, 

 and in the butterflies Arnxi-lniin /rrniiit and A. 

 prorsa, which seem to be diversely coloured 

 \ ai i. Mies of one species. Light, which is so import- 

 ant a factor in the development of chlorophyll in 

 plants, has also an influence on the pigmentation of 

 animals. Thus, apart from the etlects of keeping 

 animals in darkness, it has been shown by 1. I!. 



