Photo.
On some Points in the Collodion Process.—In your impression of this day's date (Vol. vii., p. 363.), the Rev. J. L. Sisson desires the opinion of other photographers relative to lifting the plate with the film of collodion up and down several times in the bath of nit. silv. solution; and as my experience on this point is diametrically opposed to his own, I venture to state it with the view of eliciting a discussion.
The evenness of the film is not at all dependent upon this practice; but its sensibility to light appears to be considerably increased.
The plate, after being plunged in, should be allowed to repose quietly from twenty to thirty minutes, and then rapidly slid in and out several times, until the liquid flows off in one continuous and even sheet of liquid; and this also has a beneficial effect in washing off any little particles of collodion, dust, oxide, or any foreign matter which, if adherent, would form centres of chemical action, and cause spottiness in the negative.
I find that the plate is more sensitive also, if not exposed before all the exciting fluid that can be drained off is got rid of; that is, while still quite moist, but without any flowing liquid.
As to redipping the plate before development, it is, I believe, in general useless; but when the plate has got very dry it may be dipped again, but should be then well drained before the developing solution is applied.
Mr. F. Maxwell Lyte (p. 364.) quotes the price of the purest iodide of potassium at 1s. 3d. per oz. I should be glad to know where it can be obtained, as I find the price constantly varies, and upon the last occasion I paid 4s. per oz., and I think never less than 1s. 8d.
Mr. L. Merritt will probably succeed in applying the cement for a glass bath thus:—Place the pieces of glass upon wood of any kind in an oven with the door open until he can only just handle them; then, with a roll of the cement, melting the end in the flame of a spirit-lamp, apply it as if for sealing a letter. This should be done as quickly as possible. The glasses may then be passed over the flame of the lamp (in contact with it), so as to raise the temperature, until the cement is quite soft and nearly boiling (this can be done without heating the parts near the fingers); and while hot the two separate pieces should be applied by putting one down on a piece of wood covered with flannel, and pressing the other with any wooden instrument: metal in contact would cause an instantaneous fracture.
Mr. Merritt's difficulty with the developing solutions depends most probably in the case of the pyrogallic acid mixture not having enough acetic acid. The protonitrate of iron, if made according to Dr. Diamond's formula, does not require any acetic acid, and flows quite readily; but the protosulphate solution requires a bath, and the same solution may be used over and over again.
Geo. Shadbolt.