Slough
Feb 28/39 <1>
My dear Sir/
You are quite welcome to make such mention as you may think proper to M Biot <2> of my processes for washing out by the Hyposulphite of soda (for whose properties Vide Brewster's Edin Phil Journal Vol. 1. p 8, et Seq. - p. 396 et Seq - and Vol 2. p 1 654. - Years 1819, 1820) <3> and perhaps it may be as well to send him a few specimens (unless you see occasion to the contrary) for which purpose & for your own inspection I annex a few <4>- with remarks
No 1. is a specimen Washed out with pure water (ie. as pure as our pump will afford it - NB. it contains rather a larger proportion of muriates than spring water usually does.-) It appears to be very effectually preserved - tho in other respects a very bad specimen.-
No 2. Is the same subject, more successfully photographed.*- Washed with Hyposul Soda Feb. 19.
No 3. is a trial of your mur soda applied weak but as it appeared to act violently on the dark parts its action was arrested by Hyposul. Soda - Feb. 19.
Afterwards I mixed the two washes - they answered tolerably well but I have not yet been able to use the muriate alone with success. - there is some nicety in the strength which I cannot hit off and I have in many cases found it act with such energy as to operated a nearly complete obliteration -
I would here observe that observation of this violent effect in the case of Mur. Potash <5> which I had been trying for another purpose (i.e. to operate a reversion of colour) had led me to shun the muriates.
The Hydriodate of Pot. when strong has also in some cases so completely obliterated all the work that no trace has been left.- When weak, I find it answers to your account - the yellow colour developed by heat is exceedingly curious and beautiful
The Ferrocyanate <6> is very ticklish in its use. I find that on keeping photographs washed with it in the dark - it slowly acts on the dark parts & at length obliterates every trace. How far such dilution as will not injure its preservative effect against light, will obviate this radical fault, time will shew - all I can now say is that it retards the obliteration.
Chromate of Potash preserves, but spoils the picture.-
I had been trying various modes of rendering nitrated paper more sensitive - till I read your most curious account of your processes, which opens quite a new view of the subject and is altogether one of the most singular things I ever saw. You must have hunted down the caprices of these combinations with great perseverance and patience.- When I read it I gave up further trials, your processes being so very simple & complete - I had most hopes of the Gallate of Silver which is affected by light very differently from its other salts.
No 4. is sent for the oddity of the conversion of a fair Lady into a pretty negress
No 5. is taken on Chinese paper, and the red tint contrasts remarkably with the decided black which is obtained with some other kinds of paper & in some states of the sunshine. It is
Nos 6 & 7 you will observe are not reverses of one another. Both these and Nos 4 & 5 are washed with H.S. Sod.
Nos 8 and 9 are a Lady & a Landscape just as they came off the frame, and being un-fixed will require to be viewed out of the Sun and preserved in the Brown paper in which they are enclosed - I merely send them to shew the extreme sharpness of which the Photographic process as applied to copying Engravings is Susceptible.
If you send any of these to Biot - let them be Nos 6.7.8. and 9.
Yours very truly
JFW Herschel
*your word photogenic recalls Van Mons's exploded theories of thermogen & photogen - It also lends itself to no inflexions & is not analogous with Litho & Chalco graphy.
Notes:
1. On 28 February 1839, Herschel recorded in his diary: 'Photography. Made up a packet sent to Fox Talbot of 9 specimens - 3 or 4 of wh discretionally to be forwarded to Biot. Wrote to F. Talbot', [HRHRC, W0022].
2. Jean-Baptiste Biot (1774-1862), French scientist.
3. John Frederick William Herschel, 'On the Hyposulphurous Acid and Its Compounds', Edinburgh Philosophical Journal, v. 1, 1819, pp 8-19 and pp. 396-400. And 'Some Additional Facts Relating to the Habitudes of the Hyposulphurous Acid and its Union with Metallic Oxides', Edinburgh Philosophical Journal, v. 2, 1820, pp. 154-156.
4. At least two of these are preserved in the Talbot Collection at the National Media Museum, Bradford: No. 4 is 1937-3789 and No. 5 is 1937-3791. There is also an un-numbered Herschel photogenic drawing, fixed with hypo and dated February 1839, which might be No. 6 or 7: 1937-3790.
5. Muriate of Potash, ie, potassium chloride.
6. True cyanates do not feature in photographic chemistry, being uncommon and rather unstable. In this case, references to 'cyanates' or 'ferrocyanates' should be read as meaning 'cyanides' or 'ferrocyanides'. In this case, Herschel was speaking of WHFT's method of fixing with the substance we know as potassium ferrocyanide.