31 Sackville St London <1>
19 May 1841
Dear Sir
The specimens of the effects of light on vegetable juices are very curious, it will be long ere Science will be able to account for all these anomalies. I have recently succeeded in combining with my Calotype process, the method of forming positive photographs <2> which has been studied by yourself and Lassaigne, Fyfe, & Hunt. <3>
The success is very encouraging. The positive pictures are formed in the Camera in about five minutes; they are generally invisible at first, but may be brought out by my process; – it is easy in the same way to make positive copies of engravings, by superposition & pressure – Such copies are much sharper than the positive copies obtained in the way hitherto practiced, viz. by a double process –
I will try & find another copy of my letters on Calotype & send it. I return your specimens with many thanks and will return your Pink Lady at a future time. She is now in the country.
Your letter on the existence of groups of nearly-related elements, which may be modifications of each other interested me very much. You omitted Bromine & Iodine which I think are modifications of a single element.
Yours very truly
H. F. Talbot
Notes:
1. 31 Sackville Street, London residence of the Feildings, often used as a London base by WHFT.
2. WHFT noted this discovery of a direct positive process on 17 September 1840, he designated it ‘leuceotype, or positive photogenic drawing’. His attention, however was distracted by his experiments on the developer gallic acid, and his perfection of the calotype process.
3. Herschel, Robert Hunt (1807–1887), scientist & photographic historian, Dr Andrew Fyfe (1792–1861), chemist, and Jean Louis Lassaigne (1800–1859), chemist were all working on various methods for obtaining direct positives.