Or Coeruleum Under The Name Coelin There Has Of Late Years Been

imported from Germany the cobalt blue with a tin base to which reference

has just been made. This comparatively new pigment--which likewise

contains or is mixed with gypsum, silica, and sometimes magnesia--has

the distinctive property of appearing a pure blue by artificial light,

tending neither to green on the one hand nor to purple on the other.

This advantage, added to its permanence, has conferred a popularity upon

coeruleum which its mere colour would scarcely have gained for it. A

light and pleasing blue, with a greenish-grey cast by day, it possesses

little depth or richness, and is far excelled in beauty by a good

aluminous cobalt. A certain chalkiness, moreover, somewhat detracts from

its transparency, and militates against its use in water. It is in oil,

and as a night colour, that coeruleum becomes of service, as our

present system of lighting picture galleries by gas affects the purity

of blues generally. If those galleries were illuminated by means of the

electric light, we have it on the authority of Chevreul that all colours

and shades would show as well as by day: the same purpose would be

answered by the magnesium light. Some artificial lights are the ruin of

colours; in the soda flame (alcohol and salt) for instance, yellow

chromate of lead appears white, while red ochre and aniline blue appear


Like other blues of cobalt, coeruleum assumes a greenish obscurity in

time, but like them it resists for a lengthened period both the action

of light and impure air, although chemically it is more open to the

influence of the latter, owing to its tin base. In admixture it may

safely be employed, as well as in fresco or enamel. For stage skies,

&c., in high-art scenery, the blue is admirably adapted. Now that there

are so many scene-painters who are artists--and so many artists who are

scene-painters--in bringing Nature to the foot-lights the effect of gas

on colours is of importance.


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