[In the construction of a photographic house, we beg to inform our
correspondent that it is by no means needful to use entirely
violet-coloured glass, but the roof thereof exposed to the rays of the
sun should be so protected; for although the light is much subdued, and
the glare so painful to the eyes of the sitter is taken away, yet but
few of the actinic rays are obstructed. It has been proposed to coat
the interior with smalt mixed with starch, and afterwards varnished;
but this does not appear to have answered. Calico, both white and
coloured, has also been used, but it is certainly not so effectual or
pleasant. Upon the whole, we think that the main things to attend to
are, firmness in its construction, so as to avoid vibration; ample
size, so as to allow not only of room for the operator, but also for
the arrangements of background, &c., and the sides to open so as to
allow a free circulation of air; blinds to be _applied at such spots
only_ as shall be found requisite. Adjoining, or in one corner, a small
closet should be provided, admitting only yellow light, which may be
effectually accomplished by means of yellow calico. A free supply of
water is indispensable, which may be conveyed both to and from by means
of the gutta percha tubing now in such general use. We apprehend,
however, that the old proverb, "You must cut your coat according to
your cloth," is most especially applicable to our querist, for not only
must the house be constructed according to the advantages afforded by
the locality, but the amount of expense will be very differently
thought of by different persons: one will be content with any moderate
arrangement which will answer the purpose, where another will be
scarcely satisfied unless everything is quite of an _orné_ character.]
_Dr. Diamond's Replies._--I am sorry I have not before replied to the
Queries of your correspondent W. F. E., contained in Vol. viii., p. 41.;
but absence from home, together with a pressure of public duties here, has
prevented me from so doing.
1st. No doubt a _small_ portion of nitrate of potash is formed when the
iodized collodion is immersed in the bath of nitrate of silver, by mutual
decomposition; but it is in so small a quantity as not to deteriorate the
bath.
2nd. I believe collodion will keep good much longer than is generally
supposed; at the beginning of last month I obtained a tolerably good
portrait of Mr. Pollock from some remains in a small bottle brought to me
by Mr. Archer in September 1850; and I especially notice this fact, as it
is connected with the first introduction of the use of collodion in
England. Generally speaking, I do not find that it deteriorates in two or
three months; the addition of a few drops of the iodizing solution will
generally restore it, unless it has become rotten: this, I think, is the
case when the gun cotton has not been perfectly freed from the acid. The
redness which collodion assumes by age, may also be discharged by the
addition of a few drops of liquor ammoniæ, but I do not think it in any way
accelerates its activity of action.
3rd. "Washed ether," or, as it is sometimes called, "inhaling ether," has
been deprived of the alcohol which the common ether contains, and it will
not dissolve the gun cotton unless the alcohol is restored to it. I would
here observe that an excess of alcohol (spirits of wine) thickens the
collodion, and gives it a mucilaginous appearance, rendering it much more
difficult to use by its slowness in flowing over the glass plate, as well
as producing a less even surface than when nearly all ether is used. A
collodion, however, with thirty-five per cent. of spirits of wine, is very
quick, allowing from its less tenacious quality a more rapid action of the
nitrate of silver bath.
4th. Cyanide of potassium has been used to re-dissolve the iodide of
silver, but the results are by no means so satisfactory; the cost of pure
iodide of potassium bought at a _proper market_ is certainly very
inconsiderable compared to the disappointment resulting from a false
economy.