Ordnance Survey Office,
23rd May 1860
My dear Sir,
Before publishing my Annual Report to Parliament on the progress of the Ordnance survey in 1859, in which I have given an account of the process which I have called Photo-zincography and also a specimen, I obtained the written opinion of Mr Carpmael of the Patent office, through the Solicitor of the War office, and he says we can publish any thing by that process without "being subject to any patent".
Mr Mungo Ponton in a communication to the Edinburgh New Phil. Journal of May 1839, says "In the case of the bichromate of potash, again, the salt is exceedingly soluble, and paper can be easily saturated with it. The agency of light not only changes its colour, but deprives it of solubility thus rendering it fixed to the paper."
Again I find that Mr Hunt discovered and published at the meeting of the British Association at <Cork?> in 1843, the process which he named Chromatype which is founded on the process of Mr Ponton – Mr Becquerel has also (in 1845–6) described the peculiar effect of light on the bichromate of potash, and therefore I am surprized now to learn that you could in 1852 claim to be the first discoverer of this property of the bichromate of potash upon which all these processes depend. I shall therefore feel obliged if you would state clearly what part of the process we employ in Photo-zincography you claim as your invention.
I do not as yet see any purpose to which your photoglyphic process would be advantageously employed on the Ordnance Survey, we have to reduce 16 sheets, each 3ft × 2ft to the scale of 9in × 4in, and then engrave them on copper on one sheet – if you can show us how that can be accurately and economically done it may be of use to us –
Believe me very truly yours
H. Fox Talbot Esqre