Full text of "An Account of the Processes Employed in Photogenic Drawing."


Source: https://archive.org/stream/philtrans09823368/09823368_djvu.txt


February 21, 1839. 

JOHN GEORGE CHILDREN, Esq., V.P., in the Chair. 

Captain Arthur Conolly and Lieut. -Colonel William Reid, C.B. 9 
R.E., were balloted for, and duly elected into the Society. 

A paper was read, entitled, " An Account of the Processes em- 
ployed in Photogenic Drawing," in a letter to S. Hunter Christie, 
Esq., Sec. R.S. By H. Fox Talbot, Esq., F.R.S. 

The subject, Mr. Talbot observes, naturally divides itself into two 
heads, Ñ the preparation of the paper, and the means of fixing the de- 
sign. 

In order to make what may be called ordinary Photogenic paper, 
the author selects, in the first place, paper of a good firm quality 
and smooth surface ; and thinks that none answers better than su~ 



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jperfine writing paper. He dips it into a weak solution of common 
salt, and wipes it dry, by which the salt is uniformly distributed 
throughout its substance. He then spreads a solution of nitrate of 
silver on one surface only, and dries it at the fire. The solution 
should not be saturated, but six or eight times diluted with water. 
When dry, the paper is fit for use. He has found by experiment 
that there is a certain proportion between the quantity of salt and 
that of the solution of silver which answers best, and gives the 
maximum effect. If the strength of the salt is augmented beyond 
this point, the effect diminishes, and in certain cases becomes ex- 
ceedingly small. This paper, if properly made, is very useful for all 
ordinary photogenic purposes. For example, nothing can be more 
perfect than the images it gives of leaves and flowers, especially with 
a summer sun. The light passing through the leaves delineates 
every ramification of their nerves. If a sheet of paper thus prepared, 
be taken and washed with a saturated solution of salt, and then 
dried, it will be found (especially if the paper has been kept some 
weeks before the trial is made) that its sensibility is greatly diminish- 
ed, and in some cases seems quite extinct. But if it be again washed 
with a liberal quantity of the solution of silver, it becomes again 
sensible to light, and even more so than it was at first. In this way, 
by alternately washing the paper with salt and silver, and drying it 
between times, Mr. Talbot has succeeded in increasing its sensibility 
to the degree that is requisite for receiving the images of the camera 
obscura. In conducting this operation it will be found that the re- 
sults are sometimes more and sometimes less satisfactory in conse- 
quence of small and accidental variations in the proportions employ- 
ed. It happens sometimes that the chloride of silver is disposed to 
darken of itself without any exposure to the light : this shows that 
the attempt to give it sensibility has been carried too far. The object 
is, to approach to this condition as near as possible, without reaching 
it, so that the substance may be in a state ready to yield to the 
slightest extraneous force, such as the feeble impact of the violet 
rays when much attenuated. Having therefore prepared a number 
of sheets of paper slightly different from one another in the composi- 
tion, let a piece be cut from each, and having been duly marked or 
numbered, let them be placed side by side in a very weak diffused 
?light for about a quarter of an hour. Then, if any one of them, as 
frequently happens, exhibits a marked advantage over its compe- 
titors, Mr. Talbot selects the paper which bears the corresponding 
number, to be placed in the camera obscura. 

With regard to the second object, that of fixing the images, Mr. 
Talbot observed that after having tried ammonia and several other re- 
agents, with very imperfect success, the first which gave him a suc- 
cessful result was the iodide of potassium much diluted with water. 
If a photogenic picture is washed over with this liquid, an iodide of 
silver is formed, which is absolutely unalterable by sunshine. This 
process requires precaution ; for, if the solution is too strong, it at- 
tacks the dark parts of the picture. It is requisite therefore to find 
by trial the proper proportions. The fixation of the pictures in this 
way, with proper management, is very beautiful and lasting. The 



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specimen of lace which Mr. Talbot exhibited to the Society, and 
"which was made five years ago, was preserved in this manner. But 
his usual method of fixing is different from this, and somewhat sim- 
pler, or at least, requiring less nicety. It consists in immersing the 
picture in a strong solution of common salt, and then wiping off the 
superfluous moisture and drying it. It is sufficiently singular that 
the same substance which is so useful in giving sensibility to the 
paper, should also be capable, under other circumstances, of destroy- 
ing it, but such is nevertheless the fact. Now, if the picture which 
lias been thus washed and dried, is placed in the sun, the white parts 
colour themselves of a pale lilac tint ; after which they become in- 
sensible. Numerous experiments have shown the author, that the 
depth of this lilac tint varies according to the quantity of salt used 
relatively to the quantity of silver. But by properly adjusting these, 
the images may, if desired, be retained of an absolute whiteness. He 
mentions also, that those preserved by iodine are always of a very 
pale primrose yellow, which has the extraordinary and very remark- 
able property of turning to a full gaudy yellow whenever it is ex- 
posed to the heat of a fire, and recovering its former colour again 
when it is cold.