C. B. (Birmingham). _If the hyposulphite of soda is not thoroughly
removed from a Photograph, it will soon become covered with reddish
spots, and in a short time the whole picture may disappear. If cyanide
of potassium has been used, it is requisite that the greatest care
should be used to effect its removal entirely._
W. L. (Liverpool). _A meniscus lens of the diameter of four inches
should have a focal length of twenty inches, and will produce perfect
landscape pictures fourteen inches square. It is said they will cover
fifteen inches; but fourteen they do with great definition. We strongly
advise_ W. L. _to purchase a good article. It is a bad economy not to go
to a_ first-rate _maker at once._
J. M. S. (Manchester). _You will find, for a screen to use in the open
air, that the white cotton you refer to will be far too light. "Linsey
woolsey" forms an admirable screen, and by being left loose upon a
stretcher it may be looped up so as to form drapery, &c. If you cannot
depend upon the collodion you purchase in your city, pray use your
ingenuity, and make some according to the formulary given in_ Vol. vi.,
p. 277., _and you will be rewarded for your trouble._
C. E. F. _The various applications to your bath which you have used have
destroyed it in all probability past use. All solutions containing
silver will precipitate it in the form of a white powder, upon the
addition of common salt; and from this chloride the pure metal is again
readily obtained. The collodion of some makers always acts in the manner
you describe; and we have known it remedied by the addition of about one
drachm of spirits of wine to the ounce of collodion. Spirits of wine
also added to the nitrate bath--two drachms of spirits of wine to six
ounces of the aqueous solution--is sometimes very beneficial. When
collodion is inert, and the colour remains a pale milk and water blue
after the immersion, a few drops of saturated solution of iodide of
silver may be added, as it indicates a deficiency of the iodide. Should
the collodion then be turbid, a small lump of iodide of potassium may be
dropped into the bottle, which by agitation will soon effect a
clearance; when this is done, the fluid may be poured off from the
excess of iodide which remains undissolved._
ALEX. RAE (Banff). _You shall have a private reply at our earliest
leisure. The questions you ask would almost comprise a Treatise on
Photography._
H. N. (March 30th). _1st. You will find the opacity you complain of
completely removed by the use of the amber varnish, as recommended by_
DR. DIAMOND, _unless it proceeds from light having acted generally upon
your sensitive collodion in the bath, or during the time of its exposure
in the camera; in which case there is no cure for it.--2ndly. A greater
intensity in negatives will be produced without the nitric acid, but
with an addition of more acetic acid the picture is more brown and never
so agreeable as a positive. 3rd. The protonitrate of iron used pure
produces a picture as delicate, and having all the brilliancy of a
Daguerreotype, without its unpleasant metallic reflexion--the fine metal
being deposited of a dead white; and combined with the pyrogallic acid
solution in the proportion of one part to six or ten, produces pictures
of a most agreeable ivory-like colour.--4th. The protonitrate of iron,
when mixed with the pyrogallic acid solution, becomes of a fine violet
blue; but after some minutes it darkens. It should only be mixed
immediately before using. The colour of the protonitrate of iron will
vary, even using the same chemicals. The cheap nitrate of barytes of
commerce answers exceedingly well in most cases; but a finer silver
surface is obtained by the use of the purified.--5th. We have generally
succeeded in obtaining portraits in an ordinary room, the sitter being
placed opposite and near the window: of course, a glass-house is much
better, the roof of which should be of violet glass, ground on the inner
side. This glass can be bought, made especially for the purpose, at_
11d. _the square foot. It obstructs no chemical rays of light, and is
most pleasant to the eyes, causing no fatigue from the great body of
light admitted._
_A few compete sets of_ "NOTES AND QUERIES," Vols. i. _to_ vi., _price
Three Guineas, may now be had; for which early application is
desirable._
"NOTES AND QUERIES" _is published at noon on Friday, so that the Country
Booksellers may receive Copies in that night's parcels, and deliver them
to their Subscribers on the Saturday._
* * * * *{371}
A LITERARY CURIOSITY.--A Fac-simile of a very Remarkably Curious,
Interesting, and Droll Newspaper of Charles II.'s Reign. Sent Free by
Post on receipt of Three Postage Stamps.