Gravelly Wax Negatives.—The only remedy I am acquainted with is to use the paper within twenty-four hours after excitement. I have tried the methods of Messrs. Crookes, Fenton, and How; in every case I was equally annoyed with gravel, if excited beyond that time; in fact, I believe all the good wax negatives have been taken within twelve hours. The Rev. Wm. Collings, who has produced such excellent wax negatives, 24 in. × 18 (several were sent to the late Exhibition of the Photographic Society), informs me the above is quite his experience, and that he excites his papers for the day early in the morning. The cause lies, I believe, in the fault of homogeneity of the waxed paper, arising from unevenness in the structure of the paper exaggerated by the transparency of the wax, partly, perhaps, from a semi-crystallizing of the wax in cooling, and also from its being adulterated with tallow, resin, &c. As a consequence of this, the paper is filled with innumerable hard points; the iodizing and exciting solutions are unequally absorbed, and the actinic influence acting more on the weak points, produces under gallic acid a speckled appearance, if decomposition has gone to any length in the exciting nitrate by keeping. The céroléine process, by its power of penetrating, will, I hope, produce an homogeneous paper, and go far to remove this annoyance.
In answer to a former Query by Mr. Hele, Whatman's paper of 1849 is lightly sized, and not hard rolled, so that twenty minutes' washing in repeated water sufficed to remove the iodide of potassium, and if long soaked the paper became porous, often letting the gallic acid through in the development. I have lately been trying Turner's and Sandford's papers; they require three or four hours' repeated washing to get rid of the salts, being very hard rolled. Many negatives on Turner's paper, especially if weak, exhibit a structural appearance like linen, the unequal density gives almost exactly the same gravelly character as wax, as the positive I inclose, taken from such a negative, shows. Not only ought collodion to be "structureless," as Mr. Shadbolt well expresses it, but likewise all the other substrata of iodide of silver.
T. L. Mansell.
Guernsey.
Photographic Experience.—The plan proposed by Dr. Mansell, in the last Number of "N. & Q.," for comparison of photographic experiences, will, I am sure, prove of much practical advantage and I therefore lose no time in filling up the table published in your paper:
1. Eight minutes' exposure.
2. South Wales.
3. Mr. Talbot's original receipt.
4. Turner.
5. ⅜ inch.