Handbook of American Daguerrotype | Page 7

it a proportionate tint of bromine, so as to obtain a deep rose tint,
delineations will be less marked, and the image have a softer tone. This effect has been
obvious to everyone who has practised the art. Thus I may observe that the light coatings
produce strong contrast of light and shade, and that this contrast grows gradually less,
until in the very heavy coating it almost wholly disappears. From this it will readily be
perceived that the middle shades are the ones to be desired for representing the
harmonious blending of the lights and shades.
Then, if we examine, with respect to strength, or depth of tone, and sharpness of
impression, we see that the light coating, produces a very sharp but shallow impression;
while the other extreme gives a deep but very dull one. Here, then, are still better reasons
for avoiding either extreme. The changes through which the plate passes in coating may
be considered a yellow straw color or dark orange yellow, a rose color more or less dark
in tint, or red violet, steel blue or indigo, and lastly green. After attaining this latter color,
the plate resumes a light yellow tint, and continues to pass successively a second time,
with very few exceptions, through all the shades above mentioned.
I will here present some excellent remarks upon this subject by Mr. Finley. This
gentleman says:
"It is well known to all who have given much attention to the subject, that an excess of
iodine gives the light portions of objects with peculiar strength and clearness, while the
darker parts are retarded, as it were, and not brought out by that length of exposure which
suffices for the former. Hence, statuary, monuments, and all objects of like character,
were remarkably well delineated by the original process of Daguerre; the plate being

coated with iodine alone. An excess of bromine, to a certain degree, has the opposite
effect; the white portions of the impression appearing of a dull, leaden hue, while those
which should be black, or dark, appear quite light. This being the case, I conclude there
must be a point between the two extremes where light and dark objects will be in
photogenic equilibrium. The great object, therefore, is to maintain, as nearly as possible,
a perfect balance between the two elements entering into union to form the sensitive
coating of the plate, in order that the lights and shades be truly and faithfully represented,
and that all objects, whether light or dark, be made to appear so far conformable to nature,
as is consistent with the difference in the photogenic energy of the different colored rays
of light. It is this nicely-balanced combination which ensures, in the highest degree, a
union of the essential qualities of a fine Daguerreotype, viz., clearness and strength, with
softness and purity of tone.
"So far as I know, it is the universal practice of operators to judge of the proportion of
iodine and bromine in coating the plate, by two standards of color the one fixed upon for
the iodine, the other for the additional coating of bromine. Now I maintain that these
alone form a very fallacious standard. first, because the color appears to the eye either
lighter or darker, according as there is more or less light by which we inspect the coating;
and secondly, because if it occur that we are deceived in obtaining the exact tint for the
first coating, we are worse misled in obtaining the second, for if the iodine coating be too
light, then an undue proportion of bromine is used in order to bring it to the second
standard, and vice versa."
The iodine box should be kept clean and dry. The plate immediately after the last buffing,
should be placed over the iodine, and the coating will depend upon the character of the
tone of the impression desired. Coating over dry iodine to an orange color, then over the
accelerator, to a light rose, and back over iodine one sixth as long as first coating, will
produce a fine, soft tone, and is the coating generally used for most accelerators. The
plate iodized to a dark orange yellow, or tinged slightly with incipient rose color, coated
over the accelerator to a deep rose red, then back over iodine one-tenth as long as at first
coating, gives a clear, strong, bold, deep impression.
I will here state a singular fact, which is not generally known to the operator. If a plate,
coated over the iodine to a rose red, and then exposed to strong dry quick or weak
bromine water, so that a change of color can be seen, then recoated over the iodine twice
as long as at first coating, it will be found far more sensitive when