1 HILLSIDE CRESCENT
March 28 1863
In answer to your two questions, I would reply provisionally
1st, that the calotype [illegible] of dry collodion plates is very respectable for sensitiveness, and is certainly not slow; but that I have only been doing what I immediately wanted with it, & not experimenting on that point. It permits of considerable range of chemicals; as gallic acid & acetic acid
pyrogallic & citric,
tannin & acetic; and these have each yielded good results when mixed into a gallo-nitrate by being poured on the sensitised collodion plates while still wet and dripping from the silver bath.
The qualities & colours of the pictures as well as sensitiveness of the plates were slightly different in each of the three cases, & the advantage on the whole seemed to rest with the tannin and acetic acid. – but then I have only dealt yet with an accidental strength of solutions in each of the three cases, & they may not be the best that could be arranged. Latterly I have not troubled myself about finishing the washing with distilled water, but the plates have come out well notwithstanding.
2nd I have not tried a flower in photo-magnifying, & fear that it could not be well done, or at least that I could not do it directly upon the flower itself, but only mediately upon a small negative photograph of it. If the flower is put close to a magnifying camera, the great comparative difference of distance of different parts would prevent all being in focus at once. The only plan therefore seems to be to put the flower a long way off from the camera first, and obtain a small negative, in the flat; and then enlarge that when preparing a positive from it. But at all events if any one, traveller, or naturalist, has already got a good, well defined negative of a flower on a glass plate there would be little difficulty in enlarging that for him, and rendering its minutić so plain that those who run may see them on the positive copy.
In extreme magnifyings, however, I have to improve my apparatus, as you truly indicate, if I can: and it may be slow work, especially as I have some other employment just now; but I hold myself in readiness nevertheless to make, or try to make, a more intense copy of the Teneriffe mountain view for your engraving, if you should at all desire it, & [illegible] [2 lines of deleted text] operations [illegible] be facilitated in any way thereby; & I remain
Yours very truly
C. Piazzi Smyth
H Fox Talbot Esqr F.R.S.
11 Great Stuart Street