It has been suggested that this puzzle was a great favourite among the young apprentices of the City of London in the sixteenth and seventeenth centuries. Readers will have noticed the curious brass grasshopper on the Royal Exchange. This long-lived ... Read more of THE GRASSHOPPER PUZZLE. at Math Puzzle.caInformational Site Network Informational
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Haerlem Blue Berlin Blue Mineral Blue Is A Lighter And

somewhat brighter Prussian blue, with less depth and less permanence. It
is a species of lake, having a considerable proportion of aluminous
base, to which its paler tint is due. As the stability of Prussian blue
rests in a great measure on the marvellous amount of latent colour the
pigment contains, when its particles of colour are set farther apart by
the intervention of the alumina, the permanence of its hue is
endangered. It was remarked, with respect to vitrified pigments, that
colour depends on cohesion. More or less, this holds good as regards all
pigments; but not only, as was also observed, does colour rest on
cohesion, in many instances durability depends likewise. It is only when
a colour is stable in itself that its particles will bear separating:
native ultramarine, for example, may be weakened almost to white, and
will still preserve its hue. If, however, a colour be naturally
fugitive, and rely chiefly on its extreme depth for what permanence it
possesses, that colour cannot with impunity be paled: witness the
cochineal lakes, which the deeper they are, the more durable they are
found; and so it is with Prussian blue. Antwerp blue is distinguished
from the latter by its more earthy fracture.

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