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A review of Claire’s book in the Hartford Daily Courant provides one of the most compelling anecdotes of the legend surrounding David’s investigative powers: “It is indeed a fact that Sir Conan Doyle stated in a lecture in New York that Mr. Carvalho’s powers exceeded those given to Sherlock Holmes, and were so startling that he would never dare put them into fiction!”
David seemed to have inherited his father’s spirit of innovation and experimentation. On the Frémont expedition, Solomon successfully tinkered with chemicals in order to produce photographic images in subzero temperatures and exterior settings, and later in life he patented a new process for water heating. Like Solomon, David began his career as a photographer, and when he later turned his attention to the science of ink and print, he did so with a similar curiosity and determination.
It is difficult to imagine how David managed to produce and publish “Forty Centuries of Ink” in 1904. At the time, he was supporting a family of five children, and his wife, Annie, had died in 1903. He was not working in academia, but the book is a deeply academic, if not obsessive, study, which examines how and where ink was produced since its earliest incarnations; its ingredients; how it interacted with different forms of paper, and how it was used and regarded by different cultures throughout history.
A typical passage: “The ‘Secretas’ of the twelfth century…. indicate many departures from those contained in the more ancient ones. Frequent mention is made of sour galls, aleppo galls, green and blue vitriol, the lees of wine, black amber, sugar, fish-glue and a host of unimportant materials as being employed in the admixture of black inks.”
“Forty Centuries of Ink” was published when David’s renown as a leading handwriting sleuth was spreading, and it was no doubt designed to advance his business and reputation. Early in the book, David establishes the necessity of understanding this history to safeguard against fraud: “The criminal abuse of ink is not infrequent by evil-disposed persons who try by secret processes to reproduce ink phenomena on ancient and modern documents.”