This process is a discovery of Sir John Herschel and receives its name
from the fact that both negative and positive photographs can be
produced by one process. The positive pictures obtained by it have a
perfect resemblance to impressions of engravings with common printer's
ink. The process, although not yet fully carried out, promises to be
of vast utility.
Paper proper for producing an amphitype picture may be prepared either
with the ferro-tartrate or the ferro-citrate of the protoxide, or the
peroxide of mercury, or of the protoxide of lead, by using creams of
these salts, or by successive applications of the nitrates of the
respective oxides, singly or in mixture, to the paper, alternating with
solutions of the ammonia-tartrate or the ammonia-citrate of iron, the
latter solution being last applied, and in more or less excess. I
purposely avoid stating proportions, as I have not yet been able to fix
upon any which certainly succeed. Paper so prepared and dried takes a
negative picture, in a time varying from half an hour to five or six
hours, according to the intensity of the light; and the impression
produced varies in apparent force from a faint and hardly perceptible
picture to one of the highest conceivable fulness and richness both of
tint and detail, the color being in this case a superb velvety brown.
This extreme richness of effect is not produced unless lead be present,
either in the ingredients used, or in the paper itself. It is not, as
I originally supposed, due to the presence of free tartaric acid. The
pictures in this state are not permanent. They fade in the dark,
though with very different degrees of rapidity, some (especially if
free tartaric or citric acid be present) in a few days, while others
remain for weeks unimpaired, and require whole years for their total
obliteration. But though entirely faded out in appearance, the picture
is only rendered dormant, and may be restored, changing its character
from negative to positive, and its colors from brown to black, (in the
shadows), by the following process:--A bath being prepared by pouring a
small quantity of solution of pernitrate of mercury into a large
quantity of water, and letting the subnitrated precipitates subside,
the picture may be immersed in it, (carefully and repeatedly clearing
off all air bubbles,) and allowed to remain till the picture (if any
where visible,) is entirely destroyed; or if faded, till it is judged
sufficient from previous experience; a term which is often marked by
the appearance of a feeble positive picture, of a bright yellow hue, on
the pale yellow ground of the paper. A long time (several weeks) is
often required for this, but heat accelerates the action, and it is
often completed in a few hours. In this state the picture is to be
very thoroughly rinsed and soaked in pure warm water, and then dried.
It is then to be well ironed with a smooth iron, heated so as barely
not to injure the paper, placing it, for greater security against
scorching, between clean smooth paper. If then the process have been
successful, a perfectly black positive picture is at once developed.
At first it most commonly happens that the whole picture is sooty or
dingy to such a degree that it is condemned as spoiled, but on keeping
it between the leaves of a book, especially in a moist atmosphere, by
extremely slow degrees this dinginess disappears, and the picture
disengages itself with continually increasing sharpness and clearness,
and acquires the exact effect of a copper-plate engraving on a paper
more or less tinted with a pale yellow.
I ought to observe, that the best and most uniform specimens which I
have procured have been on paper previously washed with certain
preparations of uric acid, which is a very remarkable and powerful
photographic element. The intensity of the original negative picture
is no criterion of what may be expected in the positive. It is from
the production by one and the same action of light, of either a
positive or negative picture according to the subsequent manipulations,
that I have designated the process, thus generally sketched out, by the
term Amphitype,--a name suggested by Mr. Talbot, to whom I communicated
this singular result; and to this process or class of processes (which
I cannot doubt when pursued will lead to some very beautiful results,)
I propose to restrict the name in question, though it applies even more
appropriately to the following exceedingly curious and remarkable one,
in which silver is concerned:
At the last meeting I announced a mode of producing, by means of a
solution of silver, in conjunction with ferro-tartaric acid, a dormant
picture brought into a forcible negative impression by the breath or
moist air. (See Cyanotype.) The solution then described, and which had
at that time been prepared some weeks, I may here incidentally remark,
has retained its limpidity and photogenic properties, quite unimpaired
during the whole year since elapsed, and is now as sensitive as
ever,--a property of no small value. Now, when a picture (for example
an impression from an engraving) is taken on paper washed with this
solution, it shows no sign of a picture on its back, whether that on
its face is developed or not; but if, while the actinic influence is
still fresh upon the face, (i.e., as soon as it is removed from the
light), the back be exposed for a very few seconds to the sunshine, and
then removed to a gloomy place, a positive picture, the exact
complement of the negative one on the other side, though wanting of
course in sharpness if the paper be thick, slowly and gradually makes
its appearance there, and in half an hour or an hour acquires a
considerable intensity. I ought to mention that the "ferro-tartaric
acid" in question is prepared by precipitating the ferro-tartrate of
ammonia (ammonia-tartrate of iron) by acetate of lead, and decomposing
the precipitate by dilute sulphuric acid. When lead is used in the
preparation of Amphitype paper, the parts upon which the light has
acted are found to be in a very high degree rendered water proof.--Sir
J. Herschel.
This process is a new invention of our countryman, J. A. Whipple, Esq.,
of Boston, and has been patented by M. A. Root, Esq., of Philadelphia.
It will be seen, however, from the previous pages of my work that Mr.
Root is mistaken in regard to his being the first improvement patented
in this country, although it is unquestionably the first by an
American. Of this improvement Mr. Root says: