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1994

Tachnical and Biblioflraphic NotM / Nottt ttchniquM et bibliographiqiMs

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Color Values in ^
Monochrome

A LECTURE ON

Orthochromatic
Photography

Delivered before the Canadian Institute
February J6th, J90J, by

J JOHN S. PLASKETT, B.A.,

Department of Physics, University of Toronto
/j TORONTO, Canada

With the Compliments oj the Author,

Color Values in Monochrome
by Photography

It is a matter of common ( vperience
among all photographers, that the print from
a negative taken on an ordinary plate Joes
not represent, even approximately, colors in
their true values. Everyone has noticed, for
instance, that in general, in photographs,
blue, a comparatively dark color, is repre-
sented by a tone several shades lighter than
that produced by the much brighter color,
yellow. We have grown so accustomed to
this defect of photography that a photo-
graphic print which correctly represents the
color values of the object, looks strange and,
at first glance, untrue. It is, however, not a
matter of common knowledge that this de-
fect of photography can be overcome, and
that colors can be represented in their true
values, or, what is a better term, luminosi-
ties in a monochromatic print.

Lisxht and ^" ^^® ^^^^ place, it is neces-
^ < sary to investigate tJie nature

of color and the nature of
the effects produced by it, or rather
by what causes it, on the photographic
plate. It seems hardly necessary to
state that color, as a purely physical process,

—3—

mm^^^'w :m^^^f

does not exist, but that it is a physiological
eflFect peculiar to the eye; that, without the
eye, there would be neither liglit nor color,
but merely an exceedingly rapid and, at the
same time very minute vibration or quivering-
of that hypothetical medium, filling all space,
which is called the ether. It is this vibration,
acting on the retina, that is the primary
cause of the sense of sight ; while the vari-
ous colors tnat we see are produced by dif-
ferences in the magnitudes and, at the same
time, in the frequency of these vibrations ;
the ether waves that produce the red and
orange colors being longer than those that
give rise to violet and blue. Roughly speak-
ing the sensation of red is caused by waves
in the ether about a-.'.oTF inch long, green by
waves TTirioo inch lor ,', and violet by waves
ffoiTolJ inch long. Similarly the effects on a
photographic plate are due, not to any par-
ticular co'^'- or colors, but to ether vibrations
of certain definite wave lengths, some of
these producing, when acting on the retina
the sensation of color, while others, which
strongly affect the plate, have no action on
the eye. If throughout this paper, therefore,
certain colors are spoken of as acting on the
plate, it is to be understood as referring to
the particular ether vibrations that excite
those color sensations.

Color There are three constants gen-

Constants 7''^ """if '" "^fT^ '°'°'" =

runty, Hue and Lummosity.
—4—

Tv.aK^«inMM^iBiii^3i&ii»'«aiiir7v»tt*"^^'«'%'<t?^ m^'wev^nat.

Purity ^''^ |>"rity ot a color refers

to its freedom from admixture
with any oilier color and is always judjfed
with reference to the spectrum, whose colors,
when it is properly formed, are absolutely
pure. A spectrum, appioximately pure, can
be formed by project inj^, by means of the
lantern, an image of a narrow slit in a piece
of metal in the slide carrier on the screen,
and interposing^ in the path of the rays a
prism or prisms. The narrow band of white
hg;t is broken up or decomposed by the
The prisms into a broad, brilliantly-

colored band whose appearance
spectrum is familiar to all. The general
arrangement and spacing of the colors can
be seen by reference to the upper, left-hand
corner of Fig. i, pages 24-25, which is a dia-
gram of the particular spectrum used. The
lines drawn across the diagram and lettered
are the principal absorption lines of the solar
spectrum, and answer the purpose of indicat-
ing, when their positions are known, the wave
length and color of the light at any part of
tiie spectrum. The lengths of the ether
waves decrease as you go from the line A to
the line H or from red to violet, and any par-
ticular color can be exactly defined by giving
the length of the wave producing it. Purity
of color, then, is due to light of, approxi-
mately, a single wave length, represented of
course by a very narrow band in the spec-
trum, and not to the superposition of waves
of different lengths which would produce an

—5-

!■• ^ , itnpure color. All natural colors

Natural ' „ ..

are, |j;enerally speaking, more
VrfOiOrS or less impure, and are produced

by the mi^i e of pure colors ; but all colors
appear pure tO the eye which has not the
power of esthnating, unaided, the purity of a
color, or of resolving impure or mixed colors
into their constituents. A color wliich, to the
eye, appears pure, and as nearly as possible
equal to the spectrum color, may be com-
posed of nearly all the spectrum colors.
This can be shown by interposing colored
glasses in the path of the beam of light pro-

* « , ducing the spectrum. The

Absorption ^j^^^^ .^ ^^ ^^^ ^^^ ^^ absorb,

opCCtra partially or wholly, some of

ihe colors, allowing the others to be fully
transmitted, and this is illustrated in black
and white by the diagrams in Fig. 2. The
rectangular figures are intended to represent
the spectrum of white light, while the shaded
portion represents the part transmitted by
the particular glass considered, and the
unshaded part what is absorbed. The
.esultant color of the glass by transmitted
light is evidently that produced by the union
of the spectral colors transmitted.

The hue of a color is the name
given to wh<it is commonly
known as color, without reference to other
attributes. Ordinarily when we speak of a
particular color, we mean the hue of thatcolor
and do not refer to either the purity or the

Hue

— b-

.r-flB.ylMPSfffl'

t ■■ CD c t> r

OBANtiE GLASS

GREFN CI. A;,;

BLUE CLASS

METHYL

VIOLET

■^'

.. .i .r'':;A

AURANTIA

METHYL VIOLET AND AURANTIA
Fir. i-

luminosity. Thus the hue of blue glass if
blue, although, on analysis, it is found to
contain not only blue but all the other colors
of the spectrum, in a greater or less degree,
blue and violet predominating. It is the
combination of these pure colors in a certain

proportion that produces the blue hue whtfch
is, of course, not pure.

Luminosity J,^^ '"'^"'^y °f - color is

' the relat've brightness of that
color with reference to ny standard, and is
evidertly the only attribute of color that can
be rendered in black and white. Photo-
graphy, being a process in monochrome, can
not render contrasts of color or hue, but only
contrasts of luminosity or light and shade.
That is to say if there are two hues, red and
blue, for instance, of the same luminosity, a
photograph or any reproduction in mono-
chrome should represent them as of exactly
the same shade of grey. The truth of this
statement will perhaps be more evident to
you, if you ask yourself which should be the
darker. Ordinarily, however, a photograph
will not represent them as of the same tint,
and our object is to see if we can not obtain,
in a photograph, an exact representation of
the luminosities of the object or objects de-
picted, irrespective of their colors. Evidently,
then, it is necessary, in order to make ac-
curate comparisons, to measure the relative
luminosities of colors.

Luminosity ^^ *^ ^^ once seen on observ-
r .1 ing the spectrum, that cer-

tain of the colors, such as
opecirum orange and yellow, are much

brighter or more luminous than any of
the others. The actual brightness, or
luminosity, or light intensity of the

—8—

various colors of the pure prismatic spectrum
has been accurately determined by many in-
vestigators, Frauenhofer,Crova and Lagarde,
Abney and others. Captain, or as he now is,
Sir William Abney's values were taken and
plotted out as ordinates or vertical lengths
above the spectrum diagram of Fig. i, pages
24-25, before referred to. Thus, for each par-
ticular wave length or corresponding color, the
value of the luminosity was taken, and a
length proportioned to that value was set out
in the vertical line through its position on the
spectrum diagram. The resultant curve,
drawn through these points, shows graphically
the luminosity at any part or of any color of
the spectrum. It is at once seen, from the
figure, that greenish yellow is the brightest
color, the values shading down rapidly on
either side to the red andblue.

Luminosity ?^ '^^" "°*' °^ course, be
r o. . inferred from this that, in

* natural or pigment colors,

VrfOlOrS greenish yellow is at vays the

brightest ; in fact it may be so shaded with
black as to be less luminous than a red or
blue. In order to obtain the luminosities of
colors, other than the pure spectrum
colors, which are in actual practice seldom
used, it is necessary to measure them.
There are several methods of doing this,
perhaps the simplest being to compare the
luminosity of the color to be measured, with
the luminosity of the grey produced by the

—9—

mixtureof black and white. A disc of Wack
and a disc of white card of the same diameter,
which were slit along a radius to allow over-
lappings, were placed on the same axis as a
disc, of greater diameter, of the color to be
measured and rapidly rotated. The eye de-
termines, almost instinctively, whether the
color is brighter or darker than the grey
produced. When it is judged that they are
equally bright the luminosity of the grey, and
hence of the color, is determined from the
relative proportions of black and white pro-
ducing the required grey. If the rotation
apparatus has a device for changing the pro-
portions of black and white during rotation,
the measurement is much more easily and
accurately made. By this method, and with
the assistance of Mr. A. H. Abbott, 8. A., of
the Psychological Laboratory of the Univer-
sity, who has had considerable experience in
photometry, the luminosities of a set of
colors, for which I am also indebted to Mr.
Qj|« Abbott, were determined. These

CU ♦ colors, pasted on black card-

^ *'* board, were used as a test

object, and a photograph of this test chart is
reproduced in Fig. 3. It will at once be
seen, from the card being represented white,
that the figure is a negative of the chart. In
that case, if the plate correctly rendered
luminosities, the brighter the color the darker
should be its representation. In fact the
densities of the rtrips should be proportional
to the lengths of the radial lines which repre-

F'Sr- 3-— Color Chart on Cramer " C " Plate.

sent, graphically, the measured luminosities
of the colors. The negative, of which Fig. 3
is a reproduction, was made on an "ordi-
nary " (Cramer '* C ") plate, and it shows, at
a glance, the correctness or rather the incor-
rectness of the representation. The brightest
colors, Nos. 9 and 10 (yellow and yellowish
green), instead of being represented by the
heaviest deposit, have only slightly affected
the plate, while some of the darker colors,
notably the blue (No. 17), have the greatest
action on the plate as represented by the
densest deposit.

li >
I! .

PhotOgfraphs ^^^ explanation of .this
of the curious result is easily

Spectrum "^T* '^^^" ^°" ^''^'"'"^

^ a photogfrapl. of the spec-

trum on such a plate. Fig. 4 is a reproduc-
tion of the negative and has superposed, in
addition, the spectrum chart and luminosity
curve previously referred to. The positions
of the colors and of the absorption lines are
shown by the latter, and it can at once be

I!!!

R ED |0?'0> J GY-; GRF.ttl

Fig: 4.- Photograph Spectrum on Cramer " C" Quartz Prism.

seen which of the spectrum colors are im-
pressed on the plate. It is found that the
waves giving rise to the red, orange, yellow,
and yellow-green colors have no eflf.-t on the
plate ; while waves giving rise to th ae and
violet sensations, and other waves _ .,ed the
ultra violet, beyond the limit of the visible
specirum, produce very marked deposits on
the plate. This peculiar behaviour of the
plate under the spectrum at once affords an

— 13 —

explanation for Ihe defective renderings of
color values in the photograph of the color
chirt, and will also explain the peculiarities
of color rendering so common in ordinary
photographs.

Color

Sensitive

Plates

The evident remedy for such
a state of affairs is to produce
a plate which is sensitive to
all the visible spectrum colors,
and, moreover, which is most sensitive to
those which are most luminous, and in direct
proportion to their luminosity. For if we can
photograph the spectrum correctly, we can
also photograph any other object correctly,
whose colors are always composed of spectral
or mixtures of spectral colors. And, in fact,
we can reproduce natural colors more satis-
factorily than spectrum colors, for the reason
that, although the dominant hue of the object
may be one that, if pure, would not affect the
plate, still other colors composing this domi-
nant hue may be active and help to produce
a truer rendering than if the colors were pure.

»¥•* T « 1 A plate, sensitive to wave

The Ideal , .. .. . „

lengths correspondmg to all
X late the spectral colors in proportion

to their luminosity, and insensitive to wave
lengths longer or shorter than these, has not
yet been discovered, nor, if an opinion may
be expressed, will it ever be discovered. We
have plates now, however, which are a de-
cided improvement over the ordinary type,

— «3—

B.*r-'i

and which, by the aid of a certain artifice,
\yill produce exceedingly close approxima-
tions to the ideal result.

Historical ^^* ori^^inator of this later type
Of . * of plate was, undoubtedly, the

OKCtcn late Prof. H. W. Vogel, of

Berlin, who, in 1873, observed that collodio-
bromide plates, stained with a yellow dye,
were much more sensitive to the yellow band
of the spectrum than unstained plates, and
who, after further investigation, announced
that if certain red or yellow dyes were used
to stain these dry collodion plates, their sen-
fitiveness to yellow and green was much
increased. This discovery created quite a
sensation in the photographic world, and the
action of a large number of the coal tar dyes
was investigated by scientists such as Eder,
Abney, Bothamley, Ives and others. The
introduction of the gelatino-bromide dry plate,
and its marvellous qualities sorbed photo-
graphers' attention for some time, and ortho-
chromatism (from two Greek words meaning
" correct color "), as it was called, was
allowed to lapse, and was apparentl> fc-got-

Commercial '^"\,.^"^ '" .SSa-'Sj Tailfer
p _ and Clayton at Paris patented

a method for making the
gelatino-bromide dry plate color-sensitive by
adding eosin to the emulsion before coating.
This method, improved as regards the keep-
ing qualities of the plaies, was introduced

—14—

St' .:

into England by B. J. Edwards & Co. in 1884.

. , In America, John Carbutt in-

American ^ugurated the commercial man-
ufacture of color-sensitive plates in 1886,
while later the Cramer Co. purchased the
Edward's process and so improved it that,
according to their claim, the use of color
screens was largely avoided. They called
their productions isochromatic (equal color)
plates, and these plates, which give very
good results, can be obtained in Toronto.
Many of the American dry plate manufactur-
ers have now added orthochromatic plates to
_ < the list of their products. In

French France Lumi^re Bros, have in-

troduced a remarkable series of plates sensi-
tised for varying portions of the spectrum.
Series A, sensitive to yellow and green ;
series B, sensitive to yellow and red ; and
series C or panchromatic sensitive to red,
yellow, and green. In this connection it
must be noticed that all orthochromatic plates,
as well as ordinary plates, are decidedly too
sensitive to blue and violet. In England
_, ^, f among several commercial
CngflfStl brands of orthochromatic plates,
besides Edward's, already referred to, I will
only mention two, the Ilford chromatic and
the Cadett spectrum, as these can be obtained
in Toronto, The Ilford chromatic is a very
clear working and brilliant plate, with which
excellent results can be obtained ; its prin-
cipal disadvantage is its slowness, which

"«.';-

i«?is:i.?si3«*i: ' ■■*5.- * : / :^4ii} '

I I

, practically debars its use, especially with
screen, wherever there is movement. ^

The Cadett Spectrum Plate is re-
markable in two ways: for its extreme
rapidity, being: by far the fastest ortho-
chromatic plate made, and for its sensi-
tiveness to all the spectrum colors, with
the exception of a narrow band in the
extreme red. Messrs. Cadett and
Neall have issued light filters for use
with the Spectrum plate, which enable
a true record of color luminosities, with
the exception of the dark red before
mentioned to be obtained.

The '^ *^*" "°^ ^®' *^ y®^' definitely

Thco explained why the silver salts

' in the film are rendered sensi-
tive to light vibrations of longer wavelength,
by the addition of certain dyes. Two
theories have been propounded to account for
it. According to the physical theory, the
light vibrations absorbed by the dyes are
transferred to the silver ^alts, thus rendering
them sensitive in the region of absorption.
In support of this theory is the fact that each
dye sensitises in that portion of the spectrum
which it absorbs. The chemical theory
states that the coloring matter is decom-
posed under the action of light, the complex
molecule of the dye giving rise to products,
which act as reducing agents on the silver
salts. In support of tiiis theory, in likeman-

—16-

I ■:{■:'

_:ji-'?5i^'~:-^/!JK£-

ner, is the fact that the best sensitisers are
those dyes most unstable under the action
of light.

vir A^f jf f There are, as will have been

Methods of ,- a e .u i • . • •

^ ^ ^ noticed from the historical

Sensitising sketch, two methods of
orthochromatising, or, more simply, sensitis-
ing plates. The first method is by immers-
ing an ordinary plate in a bath of the dye
solution, eosin, erythrosin, and cyanin, being
the dyes most commonly employed. The
second method is to incorporate the dye with
the emulsion in the process of manufacture.
Practically the same effects can be obtained,
but, aside from the troublesome nature of the
first process, plates prepared by bathing
have not good keeping qualities, from one to
four weeks being the limit ; while plates pre-
pared by the second method keep nearly as
well as ordinary plates. In preparing plates
by the bath method only a very weak solu-
tion of the dye is needed, one part in from
3,000 to 25,000 parts of water ; and, to
increase the sensitiveness of the plates,
although reducing their keeping qualities, a
little ammonia may be added. The plates
are immersed for one or two minutes, as a
rule, and are then dried in the dark.

T> ,* J I prepared some Cramer " C "
plates by immersion, sensi-
r^lates tising them with eosin, with

erythrosin, and with cyanin, and ihese plates
were then used to photograph the spectrum.

—17—

if it is desired to obtain exact quant itive
results from a test of this nature it is neces-
sary to form a pure spectrum on the plate by
means of a spectroscope. This could not be
arranged without special apparatus, so a
spectrum, formed as previously described,
was used and a photograph of this taken in
Spectrum ^ .-•^'"era. The results ob-

T>, , tamed by this method,

rhotOgraphs although not giving an
exact measure of the amount of light action
of the various parts of the spectrum, clearly
indicate the effects produced on the different
plates, and, when placed in the form of dia-
grams, enable comparisons to be made.
From the negatives thus obtained curves
were drawn, in the same manner as the
luminosity curve before refened to, except
that the length of the vertical lines was taken
as proportional to the light action on the
plate, or, what is the same thing, to the
density of the resulting ntn-ative. The
GraohfCal ""^^"'^^"^ curve and the lumin-
M ffirt/4 °^'*^ curve were then drawn

Method above a figure showing the

positions of the absorption lines, and evi-
dently, the more nearly these curves coincide,
the better will be the color renderings of the
plate. In the upper, right-hand corner of
Fig. 1 is the diagram representing the effect
on a Cramer "C " plate, the negative itself
being reproduced in Fig. 4, and at the other
side of ihe figure is another diagram from
the same brand. The former was taken

—18-

from a spectrum produced by a quartz prism,
which transmits the ultra violet waves, while
jflass prisms, used in the latter, and in all the
others, absorb them. It will be observed,
from the diagrams of the bathed plates, that
the general effect is to render them sensitive
to the longer waves without appreciably
diminishing their sensitiveness to the shorter
or blue and violet waves.

CommerCfal The other diagrams shown
Ortho- '" ^*^- ' were drawn, as will

chromAt'r ^® ^^®" ''^°'" '^® titles in the
figure, from negatives of the
spectrum on three different

Plates

Fig 5.— Photogrraph of Spectrum on Cramer Iso. Med.

brands of commercial orthochromatic plates,
the Cramer Isochromatic of medium speed,
the Ilford Chromatic, and the Cadett Light-
ning Spectrum. These are, so far as I know,
the only makes obtainable in Toronto. To
avoid choosing any pprticiilar brand for
experiment, the three were investigated, as
impartially as possible, and the results will be

—19—

presented with no more comment than seems
necessary for explanation. Fig. 5 is a repro-
duction of a negative of the spectrum on a
Cramer Isochromatic medium plate, and it
can at once be seen how much better an
effect is produced than on a Cramer ordinary
plate. The greatest density now is obtained
between the D and E lines, in the greenish-
yellow, nearly at the point of greatest lumin-
osity. The diagrams in Fig. i, pages 24-35,
show quite a similarity, especially between
the Ilford and Cramer, the Cadett, how-
ever, being more sensitive to the orange and
red waves,
o ' 4a. These curves show that,

Sensftiveneis ,., . ., . ..,. .

_ although the addition of a

to Olue dye or dygs tj, J he emulsion,

before or after coating, has the eflfect of
renoering the plates sensitive to vibrations
causing sensations of green, yellow, and in
some cases, red, there is still too great sensi-
tiveness, by far, to the vibrations giving rise
to blue and violet sensations, to correctly
render color uiminosities. There are two
WW .« J r methods of overcoming this

Methods 01 ..a, ,. c » u ^ • • ..

^ ditficulty : hr-,t, by dimmish-

LiOfreCtingf \„g (he sensitiveness of the
plates to the blue and violet waves, second,
by diminishing the action of the blue and
violet waves on the plate. A correction, or
even an approach to a correction, by the first
method has not yet been attained, nor does it
appear likely to be attained. The second
method, however, offers a simple means, by

absorbing part of the blue and violet waves,
of overcomiii); the difticulty. It will be
remembered that the effect of interpoHing
colored glass in the path of the beam pro-
ducing the spectrum was to absorb, partially
or wholly, some of the spectrum colors. If
then a colored glass or film can be obtained,
which will absorb most of the blue and violet
and all the ultra violet waves, and if this be
placed in the path of the beam of light enter-
ing the camera, near the lens being the most
convenient place, the luminosity renderings
should be materially benefited.
^1 A device of this nature is called

a color screen or ray filter, and
OCfCCns its appearance by transmitted
light is, in general, yellow or orange. The
absorption diagram of orange glass in Fig. 2
represents, in a general way, the absorption
caused by color screens. Screens may be
composed of colored glass, stained gelatine
or collodion film, or a liquid solution contained
in a thin glass cell with parallel sides. They
may be placed in front of, or behind the lens
of the camera, or directly in front of the
plate ; or the same object would be attained
by illuminating the subject with yellow or
orange light. The dyes commonly employed
for staining the films are some of the coal tar
series, the principal ones being aurantia,
aniline yellow, naphthol yellow, brilliant yel-
low and others, while chromate and bichro-
mate of potassium in solution are generally
used for liquid screens.

— 31 —

m-9

Fig. 6.— Photograph of Spectrut. on Ilford Chromatic and Screen.
Eff«''t of ^^® effect produced by

r' 1 " Q employing^ such screens

Cooler :>CfCCns ^hen photographing the
spectrum is shown in Figs. 6 and 7, which are
repfoductions of the negatives obtained.
Fig. 6 is a negative on an Ilford chromatic
plate using a liquid screen of a yellow color,
while Fig. 7 is a negative on a Cadett spec-
trum plate using the Cadett Absolutus screen,
which is of a reddish orange color. Again
Fig. I pages 24-25, represents, diagrammati-
cally, these results, with two others, and shows

G , BLUE B V : ViOLCf

^*g- 7 —Photograph of Spectrum on Cadett Spectrum
.ind Absolutus Screen.

—33 —

«-r

*ir

as»

the decided advantage of using screens. The
two curves are brought nearer to coincidence,
especially when using the Absolutus screen,
and the effects obtained thus approach very
closely the ideal result.

^1 r Evidently, the yellower or more

orange the screen the more blue
OCrecnS ;§ cut out, and it is easily possible
to get a screen so deep in color as to render
the blues too dark in the print, while, if not
deep enough, they wil! be too light. It will
be noticed, also, in the diagrams of the un-
screened plates, that each brand has a dif-
ferent shape of curve, and one screen will not,
therefore, suit all plates. To obtain the best
results, the screen should be so adjusted to
the plate as to absorb waves having too
vigorous an action, and to transmit freely
^1 r* J 4.4. those with too feeble an
1 nc ^aaett action. Up to the present
Screens Cadett and Neall are the

ONLY makers of orthochromatic plates who
have attempted to supply screens correctly
adjusted. They have issued two screens {' :
use with the Spectrum plate, the Gilvus and
the Absolutus. The Gilvus increases the ex-
posure about five times, and tlie Absolutus
about forty times. This increase of exposure
is due to the absorption of the most chemi-
cally active waves, and applies, of course, in
a greater or less degree to all color screens.
It is claimed that the Gilvus screen gives
correct rendering of all color luminosities but

-33—

ll 1

^^./T ■

.■-. ^

Iliii

,y all (f/^ a ff 4 f

MJl-Jg'M-'jyl t' '<f^E''J |Bc| BLUE IBV I violet'

f >.-*-f^f^<iMi ,..>egg|r£

-24—

Fiffi

•!■ »■" 1^/.*^ *ii'«" ii>.

'J. *

icilAIIEl|-C- "CWAKTZ [fKISM

I — ' T-t*»tXTlM?,cnfw ' r

— »5-

the red, and the Absolutus gives correct
values to all colors but a narrow band in the
extreme red. The Ilford Co. also supply two
screens of colored glass, a light and a dark,
increasing exposure about three and six times
respectively. The screens of course, are not
adjustable, and no claim is made as to color
renderings. The Cadett screens are, I be-
lieve, made of four stained films, two gelatine
and two collodion sealed in optical contact
between two pieces of optically worked glass,
and hence allow considerable variations in
Absorption ^^^ absorptions produced.
Spectra of "^^ese absorptions, and that
o J of the liquid screen used, are

OCreens indicated, in a rough way, by

the shaded part of the rectangle below the
diagrams in Fig. i. On comparing this with
the curve above, and with the curve for
the same plate without a screen a very good
idea of the function of the screen may be ob-
tained.

'Ill

111

IP I

liii

ilii

Method of ^^^ ^^"^^ curves will also
A J, serve to indicate the method

Adjastment ^o be pursued in adjusting
screens to plates. Take a photograph of a
pure spectrum through the screen to be tested
on the plate to be tested, measure the densi-
ties of the different parts of your negative,
and plot a curve to correspond. It can at
once be seen, on comparing this curve with
the luminosity curve, what colors have too
vigorous an action, and the screen can be

— ab—

ISKi'.^W'BK

changed to absorb more of that color. It is
essentially a method of trial and error, and,
owing to the tedious photometric measure-
ment of densities, is not suited for commercial
purposes.

Abney's Captain Abney has devised

CoIq, ^ simple instrument, which

Sensitometer forThl" "'" ''"''"'■""^'-

tor the same purpose. He
takes, usually, four pieces of colored glass,
red, yellow, green and blue, which transmit
approximately pure colored light. The
luminosity of the light transmitted by each is
accurately measu^-d, and behind the three
lightest are introduced rotating sectors, or
patches of developed grey of such density as
to reduce their luminosity to that of the
darkes . Then red, yellow, green and blue
light, all of equal luminosity, will be trans-
mitted, which should give, on a pUte behind
a correctly adjusted filter, patches of equal
density. As the glasses need only be very
small, the whole apparatus, with the plate to
be tested, can easily be placed in a quarter
plate printing frame, and hence is quickly
and cheaply tested. If the patches are not of
equal density, and this can readily be judged
by the eye, the filter must be changed to
absorb more of the color giving too dense a
patch, or less of the color giving too light a
patch. This, as before, is a method of trial
and error, but with the advantage over the
former of avoiding the tedious measurement

—27—

]^r

Wi'

7C <'*if 0' f

of densities, and of overcoming possibly
errors due to improper exposure or develop-
ment, while the results obtained with screens
so adjusted, should be equally good.

Results ^^® results obtained in photo-
e graphing the spectrum

decidedly the
Spectrum orthoch'-omatic

show
advantages of
over ordinary
plates, the advantages of screened over
unscreened orthochromatic plates, and
finally the advantages of scientifically
screened orlhochromotic plates over all
others. In photographing colored objects of
all kinds we will see that the same results
obt£tin as in the photographs of the spectrum.
This is what is to be expected when it is con-
sidered that the colors of all objects are either
spectral colors or mixtures of spectral colors.

ja *. p Asa test object, a color chart

Results from , . .

was construe) ed by pastmg
VrfOlOr Chart colored paper on a sheet of
black cardboard. Twenty-four different
hues, intended to represent spectral colors
as closely as possible, were arranged on the
circumference of a circle and four different
shades of grey inside. At the two lower
corners of the card ten other colors were
arranged in two squares. As a guide to the
colors arranged on the circumference I may
say that No. i is red. No. 5 orange. No. 9
yellow, No. 13 green. No. 17 blue. No. 21
violet, and the intermediate strips are inter-
mediate in hue. As before mentioned, the

-28—

1/'

ifO

radial lines around the circumference repre-
sent, by their lengths, the luminosities of the
colors, and, in the same way, the lines
arranged between the two colored squares
represent the luminosities of the strips com-
posing the squares. It must be distinctly
remembered that all the figures of this chart
are reproductions of negatives, and hence, in
a correct rendering of the color luminosities
of the strips, the densities of the patches of
grey representing the strips should be exact-
ly proportional to the lengths of the lines
^^ 4, beside them. Fig. -i, already

Ordinary . ^ • '.

' mentioned, is a negative on a
Plates Cramer " C " plate and imme-

Fig. 8- Photograph Color Chart en Cramer Iso Med.
diately shows the very faulty record given by
ordinary plates. Three other brands of
ordinary plates were tried, and, although the

— 29 —

Photogrraph of Color Chart on Ilford Chromatic.

Fig:. lo.
Photograph of Color Chart on Cadett JSpectrum.

-30-

differences were not very marked, the
Cramer was undoubtedly the best. Fig. 8 is
Oftho- ^^^of" •f>eneg:ative on a Cramer

chromatic ]T '"^'^'""' ^^^^^' ^''«' 9 a"

Plates ^ Chromatic and Fig. lo a

Cadett Spectrum. These three,
although giving a much better result than
ordinary plates, are still far from perfect.
The patches representing the blue and violet
strips are mt.ch too dense, while the yellows
Advantage ^""^ "o»«le"se enough. When

of Screens Tr "'^ '^^ "^""^ '^'"^^^ ^'

betore, a screen to absorb
some of the blue and violet, the improvement
>s decidedly marked and in three of the
remaining figures the values of the circular
set of strips are as nearly as can be judged
by the eye, approximately correct. Figs. 1 1
and 1 2 are on Ilford Chromatic plates with the
Ilford light screen and a liquid screen of a
full yellow color respectively. Figs. 13 and
14 are on Cadett Spectrum plates with the
G.lvus and the Absolutus screens respectively.
The two lower squares form a severer lest
of the qualities of plates and screens than
the circle, and it is with these that the final
comparison must be made.

Composite '^ '** evident, from the compari-
Nature of ''°" °^ spectrum and color chart
Colors "^&at'V'-s on ordinary plates,

that the values given by the
latter, although far from correct, are not so
faulty as we would be led to expect from the
photographs of the spectrum. The cause of

—31 —

Iff. II.

Photojfraph of Color Chart on llford and Ilford Screen

*• ■.!

Fi^. 12.

Photogrraph oi Color Chart on UforC, and Bichrome

Screen.

—32—

""■W^ r'.iMP'T^I- a.;

. «...j>':«apuMBWe

Photosrraph ot Color Chart on Cadett Spictrum and
Uilvus Screen.

Fib:. 14.

Phot-graph of Color Chart .,.. Cndclt Spectrum and

Ahsolutus Screen.

this IS evident when the colors are analysed
spectroscopically. h will be found that they
do not reflect one or two colors only, but,
generally speaking:, all the colors but one or
two, which are, of course, complementary to
the dominant hue. The composite nature of
these colors, and indeed of all colors in nature,
•sanaid lo their coriect rendering. If the
colors of natural objects were pure spectral
colors, the ordinary plate, being sensitive
only to the blue and violet, would not be
affected by j^reen, yellow, orange or red, and,
as a consequence, they would alike be ren-
dered, in the print, as one mass of black
without form or detail.

Colored '^ '* * natural transition from
PictufM *^* pigment colors on the test
^"'" chart to those used in paintings
and other colored pictures, and similar effects
will be noticed in their reproduction. In all
colored pictures, especially old paintings or
pictures containing deep brown or other
dark tints, the use fa screen, comparatively
deep in color, is necessary to obtain the values
of the different colors, and indeed it seems to
be impossible to obtain detail in the shadows
without such a screen. In the subject chosen
for reproduction (no figures ; slides shown in
original lecture) this is shown in a marked
degree. The difference between the results
obtained on ordinary and on orlhochromatic
plates without a screen is not very marked
but when screens are used the improvement

—34-

'■".^m

"* very noticeable. Not only i« ,he effect
much more brilliant, and free fron, the flatness
which characterize, the former, but also de-
tail iH obtamed in the browns and reds which
.« entirely absent in the unscreened pictures.
Moreover ,t is quite evident from the result,
that a deep screen (the - Absolufus") jjives
much hr ,r rendering than a plain full yellow,
or orangre screen, and that, by the use of a
properly adjusted screen, effects completely
satisfying to the eye can be obtained.

Flowers ^^^ '''°'°" °^ nature, on the
other hand, are chiefly of in-
terest in this connection as they are present
m flowers, fruit, etc., and in landscapes.
Flower photography is another branch of the
art ,n which orthochromatic plates offer de-
cided advantages over ordinary plates. The
use of a screen, however, i. not so indispens-
able ,or . ,e best results as in the case of
pictures. Indeed, if there are no blue or
violet flowers, better results will often be
obtained without a screen, as its use. espe-
cially If at all deep in color, seems to intensify
he yellows, causing them to appear too white

LllITT- " ''""^- An exception must
be made to this statement in the caseof.he
Absolutus screen, which, when used with the
Spectrum plate, always possesses a decide '
advantage. A screen is necessary, if there
are blue or violet flowers, to cut down their
actinic value and to prevent them appearing

tr.. f 'V^f^''"'- These points are illus-
trated in the slides (no figures) of crimson.

—35—

P-nk, and yellow roses, and violcc-. The
or l>ochron,a.ic pla.es wi.l.ou, a sceen give

both ,he volets are by far ,00 light. The use
of a yellow screen, although bringing the
volets to their correct tone, ntakes the yellow
roses too light, and the only method of over

ad u d b, „„, „, .,.^ „,^„_^^^^ ^

Landscapes

;s '^^'^ '^^^ and. to most photo-
p.-aphers, the most important
l2Tl "' ■"•""-'"P"^. 'andscapes', also
exh b„s .„ comparative results the advant-
ages of color sensitive plates. At this time
of the year, wmter. when landscapes contair
■ttle else but black and white, orthochroma"
UC pla.es naturally, do not show such
marked advantages over ordinary plates as
■n s.nnng, summer or autumn. Thev still

sufficient to recommend their use. These
r».nts are : first, used with or without a
screen better detail in the snow can be
secured, second, parts of the landscape
uncovered with snow show much more ^e a'i

screen, than on ordinary plates, third
cloud ,„ be obtained without special car^

as the landscape, and here also a screen is
an advantage. But it is chiefiy in the o h
reasons that the advantages of orthochroma-

-36-

fied ihal no one who makes a fair .rial of

or..,ochroma>ic and ordinary p.a.e. 1 he

an,e .nhjec. „i„ be ever a^ain con.en. Juh

the faulty records „f ,he la„er. These

scenes, are dlustra.ed by slides, are: im-
proved rendering of the various shades of
green .n the foliage, the genera, brightening

ing?„ t" "" " """ "' ""^ "^y- 'he clear^
■ng up of an excess of haze obscuring the
d-tance. and, finally, „,e p„,,ibiliTy „f
Qouds "blaming, especially when a

and l»„H '"'•'^'''^ ''"■"" '* "'«d, clouds

and landscape m the same negative. Even

wdl produce a very natural tone in the skv
gradually lightening as it approaches tfe
honzon, and any clouds, even very light and
fleecy ones, will show in the printf as i„
nature, as white on a darker background

Screens ^''^ foregoing remarks indicate

the use „f '" ""^ ""'•'""'J' °f <^»«'.

the use of a screen is necessary if true color

values are desired. In ,he reproductio^ of
P^mentsinany form a screen is necessary
and .t ,s generally desirable in other subjects
as flowers and landscapes. If these attl;
objects contain yellows and greens Zy,
the use of a screen would not cause a marked
d,«^^rence in the result, but if there are Wue'

~.:. 't;„rd::;rr";cf ••''""^ "'"-

vn their actinic value to cor-

—37—

respond with their luminosity value is neces-
sary.

Varieties ''^'* regards the kind of filter,
of Screens *''^ ""^^^ desirable, if it could
be obtained of the correct tint,
would be a piece of optically worked colored
glass. But, as will readily be seen, it is
practically impossible to obtain a suitable
color. The liquid screens, such as the
Bausch & Lomb ray filter, present the ad-
vantage that their color can be varied by
altering the strength of the solution, but
possess the drawback that the liquid evapor-
ates knd requires replenishing, and that the
inside of the cell gets dirty and requires
cleaning, which is troublesome to accomplish.
Screens made of stained gelatine or collodion
films, eit^^er coated on glass or sealed be-
tween two glasses, can be obtained of any
desired tint and can consequently be cor-
rectly adjusted. There is no liquid to be
spilled and evaporate, but care has to be
taken to keep them from the light when not
in use, as there is danger of fading.

Cadett '" working with the Cadett spec-

_ trum plates, it would be advis-

OCreens able to use the screens they
supply, as much better results would be ob-
tained than with any screens not specially
adjusted. The Gilvus can be used for all, or
nearly all landscape work, and does not in-
crease the exposure sufficiently to prohibit
instantaneous work. The Absolut us should

-38-

be used where absolutely correct values are
required, and when the increase of ex josure
permitsr. If both can not be obtained, the
Gilvus would probably be the most generally
useful for amateur^. For use with the Ilford,
Cramer and other orthochromalic plates it is
useful to possess two screens, a yellow and
an orange, the yellow answering for ordinary
landscape work, and the orange when there
are fleecy clouds to be reproduced, or in

Unadjusted Ph°t08:'-aphing pictures. The
Ilford screens, light and dark,
OCrCCns ^^de of colored glass, would

answer for most purposes, and are quite con-
venient to use. Whatever screen is used,
however, it is essential that the glass or
glasses of which it is composed be perfectly
plane and parallel, or distortion, and conse-
quent loss of definition, will inevitably result.

ManipolatiOn ^^^°^^ concluding a few
of OrthocLfO- ••^'"^'^^^^ about the working
. , Tif A * °^ orthochromatic plates
matlC Plates ^j^ht be of service to be-
ginners in the method. It has often been
urged against their use that they are trouble-
some to manage in development, and of poor
keeping qualities. Orthochromatic plates,
certainly, can not be exposed so freely to the
regular ruby light as ordinary plates without
danger of fog, but ample light can be used,
especially in the latter stages of development,
to properly watch progress ; and while, per-
haps, not keeping so well as ordinary plates

—39—

Exposure

their good qualities are preserved much
longer than is generally imagined ; for in-
stance, a box of Ilford Chromatic plates,
which I purchased nearly a year ago, yields
excellent negatives without any sign of de-
terioration.

When using slow orthochromatic
plates, such as the Ilford Chro-
matic and the Cramer Iso. Med., ample ex-
posure is required. For, while they seem to
possess great latitude as far as over-exposure
is concerned, the evil effects of under-exposure
are far more marked than is the case with
ordinal^ plates. In my experience with these
two makes not one plate has been over-
exposed, although, as I thought, ample ex-
posure was always given. The Cadett Spec-
trum plate, as is natural with a very fast
plate, has not so great latitude, and care
must also be taken not to over-expose. As a
guide to the exposure required, if we take the
typical case of an ordinary landscape on a
bright day in summer, at three o'clock in the
afternoon, and if the lens be stopped to f-ii,
the Ilford Chromatic would require an ex-
posure of at least iV second, the Cramer Iso.
Med, 1^2 second, the Cramer Iso. Inst. -3V
second, and the Cadett Spectrum ^^- to j^jj
second, depending on the speed number of the
emulsion. If a yellow screen were used these
exposures would be increased four or five
times, and the slow plates could not be used
^or instantaneous work, even with an aperture
of f-8. ^

—40—

Dark Room '^''^ developing light that
. , j^ >*afe to use in working orlho-

i^ISfntS chromatic plates depends, of

course, on the plate. Plates that are insensi-
tive to red can be worked in a deep ruby light
without fear of fog, but plates sensitive to red
can not be safely exposed to such a light.
For plates of the former class, of which the
Ilford and Cramer are examples, the regular
ruby and orange glass may be used, with the
illuminant turned down low, and the plates
exposed to the direct rays as little as possible
during the early stages of development ;
when development is nearing completion,
however, the light may be turned up to ex-
amine progress without danger of fogging the
plate. For plates of the latter class, of which
the Cadett Spectrum is an example, develop-
ment will either have to be conducted in
darkness, or with a light which transmits a
color to which the plate is insensitive. Cap-
or tain Abney recommends two

_ , ^ gelatine films, formed from dry

l^IS^ntS plates fixed and washed, one

stained deeply with methyl violet, the other
with brilliant yellow, and bound together film
to film with lantern slide binding strips. The
absorption spectra of methyl violet and
aurantia, which is similar to brilliant yellow,
are shown in Fig. 2, and it will be observed
that, while methyl violet transmits a narrow
band in the extreme red and some blue and
violet, aurantia transmits everything but blue
and violet. If the two are combined the

—41—

result W.1I be. as shown in the lower diagram v
to transmit only the extreme red. and snch a
combmat.on. if carefully used, should be safe
w.th the Spectrum plates. Sanger Shepherd
recommends three films, of methyl violet
naphthol yellow, and aurantia. and for a com-
bination still more safe naphthol yellow
aurantia. brilliant green, and fuchsm. The
Cadett safe light, which can be purchased
ready to use, will probably prove mo.t suitable
for amateur's use, and is. I believe, composed
of a film sta.ned with methyl violet and two
colored glasses, yellow and yellow green
Even when usmg these safe lights it would do
"o harn, to keep the tray covered, during de-
velopment, as much a« possible.

Developers ^^® developers to be used
. ^.«. ^°'' ^''thochromatic plates do

not differ materially from those ordinarily
employed. In fact any developer suitable
tor an ordinary plate can be used on an
orthochromatic plate. There is one point to
be guarded against, however, when working
with slow plates such as the Ilford and
Cramer Medium, and that is to use only
about one half the usual quantity of the
developing agent or reducer, pyro, metol,
e.konogen, or whatever is used, with the
usual quantity of alkali, and to make up the
Excess of ''^'*"^« with water. It will be
Contrast ^"""'^ *^^^ '^ ^ developer of full

the negative will be too dense and contain

—42—

too much contrast to give harmonious resuUs.
This peculiarity, the great density giving
powers of orthochroriiatic plates, should be
of great advantage for any subject whose
contrasts it is wished to increase, for instance
a landscape flatly lighted, or on a cloudy day.
For such an effect the proportion of develop,
ing agent might be increased with advantage.
Very fast plates, such as the Cadett Spec-
trum, do not require tins precaution and in
fact the developers for these plates call for a
larger proportion of reducer, or rather for a
smaller proportion of alkali. The object of
this, no doubt, is to prevent chemical fog
which is more likely to occur with fast plates,
but in my experience I had no difficulty with
fog, and the development proceeds in exactly
the same manner, only more slowly, as r ith
ordinary plates.

Necessity for ^" ^^^"^ ^^^ manipulation of
c . orthochromatic plates differs

cspenence only in the points mentioned
from that of ordinary plates and no difficulty
should be experienced in their successful
handling. It must be remembered, however,
that any change in materials or methods in
photography requires experience to become
familiar with the new conditions imposed,
and hence that perfect results should not
be expected to be attained with the first
box of plates.

—43-

Conclusion '" "•""cl'-sion I can only hope

we'la. th. r •"'"',' '""'' ""deeded, as
wej a. the hm.ts of a single lecture allow

'" "'f'"^ you familiar with the n,ain po „T,'
about orthochro«,ati.m and the correcret
denng of color values. 1 ,ru„ alto T.

:::: ::- r -''"' -"" »■■- ---i,?:
;-.ou „ii, ...:f'.:-'j^z,:::z:::

the ordinary plate, and will ,h„s l,as,e„The
day when its faulty record win be repTa ed

X^,Z,r ™"deri„g of color lu„,i„„sities
given bv the orthochromatic plate.

—44—

The same careful attention in all detail, it
given to the other Brands of Plates manufac-
tured by Messrs. Cadett & Neall, Limited,
Ashtead, Surrey, England, and the Trade can
be supplied by

MESSRS. EAKINS & FERRIS,
Sole Importers,

Toronto, Canada.

Ordinary Plates
Professional Plates
Special Rapid Plates
Lightning Plates
Spectrum Plates
Safe Lights
Screens

'limwsfAiiESiijme'iSftsm.wm--^ . v»«»rram0svw

"»fP IftT^'MiCi*--', -" ,1,-

«• J»fl^^ai«f."^vJj"-?' - -^ 'i^yn '