[We have submitted this Query to DR. DIAMOND, who informs us that he
never adopts the practice of washing off the developing fluid, and
considers it not only needless, but sometimes prejudicial, as when such
washing has not been resorted to, the hyposulphite solution flows more
readily over the picture, and causes none of the unpleasant stains
which frequently occur in pictures which have been previously washed,
especially if hard water has been used. But besides this, and the
saving of time, the doing away with this unnecessary washing economises
water, which in out-door practice is often a great consideration. DR.
DIAMOND would again impress upon our readers the advantage of using the
hyposulphite over and over again, merely keeping up its full strength
by the addition of fresh crystals of the salt from time to time, as
such practice produces pictures of whiter and softer tone than are ever
produced by the raw solution.]
_Colouring Collodion Pictures_ (Vol. vii., p. 388.)--A patent has just been
taken out (dated September 23, 1852) for this purpose, by Mons. J. L.
Tardieu, of Paris. He terms his process _tardiochromy_. It consists in
applying oil or other colours at the back of the pictures, so as to give
the requisite tints to the several parts of the photograph, without at all
interfering with its extreme delicacy. It may even, in some cases, be used
to remedy defects in the photographic picture. The claim is essentially for
the application of colours at the back, instead of on the surface of
photographs, whatever kind of colours may be used. It is therefore, of
course, applicable only to photographs taken on paper, glass, or some
transparent material.