I must confess that I know not what apology to offer for thus troubling you, but I trust that my desire to be further acquainted with the process of preparing the Calotype paper may be pleaded by me as an excuse. In the Civil Engineer and Architects Journal for August 1841, I saw an extract from a paper said to have been read by you before the Royal Society on the method of preparation<1> I obtained the materials, making the Nitrate of Silver myself from pure silver precipitated from a Solution, and followed the directions to the letter, but I found that the paper after being washed with the first Solution of Nitrate, on drying turned a light brown, this I attributed to the caustic effects of the nitrate concentrated by the drying, however, I proceeded, and dipped it in the Iodide of Potassium, dried &c and the paper attained a faint yellow colour, the brown disappearing, I then washed it with the mixture of Nitrate and Gallic acid (I used pure crystallized gallic acid) but I found on drying the paper turned dark brown without being exposed to the light, this I repeated many times, but with the same results. I then varied the process in many ways, likely and unlikely but on drying, it invariably darkened. I then suspected that the Nitrate having been exposed to the light while in solution, might be the cause of the darkening, and I made more Nitrate, keeping it from daylight, but I did not find any difference I then tried weakening the Solutions but found the effect the same, only in a less degree. I suppose there must be something in the manipulation of which I am still ignorant and without some clue, I may go wandering after the cause of error long enough without finding it
I have lately made use of the paper immersed in Salt Water, which I use in proportions 450 grs to 8 oz water, and after dipping for ½ minute or so, during which time I brush it to insure its uniform wetting I dry and then wash it with the Same Solution of Nitrate which in the other method is mixed with the Gallic Acid viz 100 grs of Crystallized Nitrate in 2 oz Water with 1/6 of its volume of strong Acetic Acid. I found it required 3 separate washings of this solution to produce a proper effect, and then the darkening was rather slow taking about 30 min: You mention in one of your Papers on the method of preparing this Sensitive paper that the proportions of the ingredients, are important, as naturally affecting the mutability thereof
I found that a Camera with a conventional fixed object glass would not afford light enough for taking pictures so I have obtained a lens 5½ inches diameter having about 12 in focal distance and I expect I shall now have abundance of light
I know of no other way than that of addressing you to obtain the information I require, and the liberality displayed by you in so freely presenting to the Public your discoveries in this interesting Subject, induce me to hope that you will not consider this lengthened communication an intrusion on my part for which I consider myself bound again to offer an apology
And remain Sir Yours very respectfully
John Dickinson Brunton
William Henry Fox Talbot Esqre
1. WHFT, "An Account of Recent Improvements in Photography," read before the Royal Society at the 10 June 1841 and widely reported on in the press.