Mr Niepce de Saint Victor, <1> one of our most renowned scientific men, has told me that, through your researches for the improvement of photography you have discovered a peculiar property to both gum and gelatin, when one of these substances is combined with the bichromate of potassa. <2> In that state and used as a kind of coat, the substance thus mixed, if dried and exposed to light should become insoluble in water, but might swell if getting humid.
Some years ago, I have lost the use of my eyes, and I try to get perfect a writing process, approved by the Institute of France, and I thought, Sir, of making out the best of your discovery, for an invention of mine, namely: a relievo-writing process for the use of the blind. <3> But Mr Niepce de Saint Victor not having been able to give me the exact proportions of the mixture of gum and potassa, I feel so confident, Sir, in your kindness, that I make myself certain of your cooperation in the philanthropic end which I aim, and I grant you, Sir, a thousand thanks for the answer, so precious for me, you will make to my queries.
I am, Sir, with gratitude, your most humble and obliged servant,
rue de la Bourse, 6, Paris.
April 10, 1863.
1. Claude Félix Abel Niepce de Saint-Victor (1805-1870), photographic experimenter.
2. This was the chemical basis of WHFT's 1852 Photographic Engraving and 1858 Photoglyphic Engraving processes.
3. No information has been traced so far about Duvignan or his invention.