The Carbon Process

The carbon tissue is seldom prepared by photographers. However, for the

sake of completeness, we shall give the formula of the mixtures most

generally employed, and describe the manner of coating the paper on a

small scale.



Preparation of the Tissue.--The gelatine generally recommended to

compound the mixture is the Nelson's autotype gelatine. Coignet's gold

label gelatine, mixed with a more soluble prod ct, such as Cox's gelatine,

for example, gives also excellent results.



Gelatine 110 parts

Sugar 25 parts

Soap, dry 12 parts

Water 350 parts



The coloring substances consist of:



FOR ENGRAVING BLACK.

Lamp-black 20 parts

Crimson lake 2 parts

Indigo 1 part



FOR WARM BLACK.

Lamp-black 3 parts

Crimson lake 3 parts

Burnt amber 2 parts

Indigo 1 part



FOR SEPIA

Lamp-black 2 parts

Sepia of Cologne 18 parts



FOR PHOTOGRAPHIC RED BROWN.

India ink 3 parts

Crimson lake 4 parts

Van Dyck brown 4 parts



For blue, Turnbull's blue is employed; for yellow, light chrome yellow;

for red, carmine dissolved in aqueous ammonia, evaporating, then adding

water, etc. (See further on.)



To prepare the mixture, dissolve the sugar and soap in the cold water, add

the gelatine, let it soak for an hour, then dissolve it in a water bath

and mix by small quantity the colors finely ground together and wetted to

the consistency of a paste. After filtering through flannel the mixture

is ready for use.



For coating, the method devised by Mr. Alf. Harman has been found

excellent in the hands of the writer, not only for the purpose in

question, but also for coating paper with gelatinous or viscous (gum

arabic) preparations.



"Take two tin dishes, such as used for the development of the carbon

prints; arrange one on your bench tilted to an angle; the lower angle is

intended to receive the warm water for keeping the gelatine mixture to a

proper temperature. Into this angle of the tray arrange another tray

somewhat smaller, and keep it from touching the bottom of the outer one by

the insertion of any small article that will suggest itself. Into the

inner tray the gelatine mixture is to be poured."



"The actual making of the tissue can now be proceeded with, and is so

simple and certain as not to be believed until put to the test. Purchase

a roll of paper-hanger's lining paper of good quality, cut it into widths

of about one and a half inch less than the width of your inner tray, and

in length of, say, thirty inches. For the success of the operation it is

necessary that the paper be rolled up the narrow way. Now having just

sufficient water at a temperature of 100 deg. Fahr. (38 deg. C.) into the

outer tray, pour the gelatine mixture into the inner one, and take one of

the lengths of rolled paper, and, holding it by both ends, gently lower it

on the surface of the gelatine; then at once slowly raise the end of the

paper, which will unroll itself and become beautifully coated in far less

time than it takes to describe. Twenty sheets may be coated in a quarter

of an hour, and be equal in all respects to that made by the most

expensive machine."



In the description of this method of coating, Mr. Harman does not explain

how the gelatine should be allowed to set before hanging up the paper to

dry, which is, however, obviously important. It is as follows: Place on

the tray a smooth board a little larger than the sheet of paper, leaving a

small space at the end furthest from the body, and slowly, without a stop,

draw off the paper, prepared side uppermost, on the board upon which it

should remain until the gelatine is set. If the paper curls up, wet the

back a little with a sponge before coating.



The following coating method, due to Mr. Chardon, is excellent for sheets

of paper of the ordinary photographic size, 18x22 inches.



On a glass plate placed on a leveled stand, is laid a sheet of paper

previously wetted, which is then flattened into contact with an India

rubber squeegee, taking care to remove the air bubbles interposed. The

quantity of gelatine necessary to coat the paper is regulated by means of

a glass rod held by an iron lath, which serves to handle it; at each end

of the rod is inserted a piece of an India rubber tube whose thickness

regulates that of the gelatine layer. The mixture is poured from a small

teapot, at the opening of which has been adapted a bent glass tube about

three-sixteenths of an inch in diameter, between the rod and the lath, so

that by a simultaneous motion, one can equalize the gelatine as it is

poured on. When the gelatine is set the paper is hung up to dry. In

drying, the gelatine contracts, and, necessarily, causes a deformation of

the tissue, which curls up at the edges and loses its planimetry. To

prevent this, while the gelatine is almost dry, the tissue is placed under

pressure until quite desiccated. Dumoulin advises to apply on the film,

while still soft and tacky, a wooden frame, which, by adhering to it.

keeps the tissue perfectly plane as it dries.



[Chardon's method of coating]



Sensitizing.--The tissue is sensitized in a bath of potassium bichromate.

The degree of concentration of the bath, which varies from 2 to 5 per

cent. of water, is important. The tissue sensitized in a weak bath is

less rapidly acted on by light and yields more contrasts than when imbued

in a concentrated one. The former should consequently be employed for

printing weak negatives, and the latter for those which are intense. A

bath compounded with 30 parts of potassium bichromate, 1,000 parts of

water and 2 parts of aqueous ammonia, is used for printing negatives of

the ordinary intensity, the tissue being, then practically of the same

sensitiveness, a silvered paper insolated to obtain a print not

over-exposed. For intense negatives the ammonia should be discarded and

replaced by the same quantity of chromic acid.



The time of immersion has also a certain influence on the results. The

less the tissue is allowed to absorb the solution the less sensitive it

is, but also the more the tendency of the half tints to be washed off

during the development. Generally the tissue should remain immersed until

it lies flat and the edges just commence to curl up, unless white and

black impressions are desired, but even then it is preferable to operate

as said above, using a bath at 2 per cent.



For use the bichromate bath should be cooled down to 15 deg. C. (59 deg.

Fahr.), and much lower in summer, say 10 deg. C. (50 deg. Fahr.), and kept

at about this temperature by placing pieces of ice around the tray. At 20

deg. C. (68 deg. Fahr.) the prints are more or less granulated; above this

the gelatine is softened and the reticulation greater; at 25 deg. C. (75

deg. Fahr.) it may dissolve.



The addition of alcohol to the bichromate bath--sometimes recommended to

harden the film and allow it to stand a higher temperature, and to hasten

the desiccation of the tissue--is objectionable, for the spirits tend to

reduce the bichromate, which is transformed into the green salt, and,

therefore, a partial or complete insolubilization of the gelatine is the

result.



Aqueous ammonia added to the sensitizing solution has for its object to

permit one to keep the sensitive tissue for a somewhat longer period, but

it renders it less sensitive. If enough be added to turn the solution

yellow weak prints are obtained.



The bichromate bath should be renewed often. It does not keep owing to the

presence of gelatine and other organic matters which it dissolves and

which cause the reduction of the chromic salt even in the dark. The

tissue prepared in such a bath is not very sensitive and the image

develops with difficulty, and even cannot be developed at all.



As said above, the tissue is well sensitized when its edges commence to

curl up. It is then removed from the bath by drawing it on a glass rod

fixed at the end of the tray, and placed, prepared side down, on a

slightly waxed glass plate, rubbing it with an India rubber squeegee to

remove the superflous liquid, when it is hung up to dry.



While wet the bichromated tissue is insensitive; the sensitizing can

therefore be made by daylight, but the drying should of course be done in

the dark room, that is in a room lighted by a candle or the sunlight

filtered through a deep orange window glass.



Caution.--The soluble bichromates are very poisonous. By absorption they

produce skin diseases not without danger and very difficult to cure. Hence

when handling the wet tissue the fingers should be protected by India

rubber tips, and any yellow, stains on the hands should be rubbed with a

dilute solution of aqueous ammonia, and the hands well rinsed in water.



Drying.--When the tissue dries rapidly it adheres well on the support

upon which it is applied for developing and yields brilliant images which

are easily cleared. On the other hand, were it allowed to dry slowly the

adherence would not be so complete, the image dull and developing with

difficulty. They may even refuse to develop at all from the

insolubilization of the gelatine.



In winter and in the cool days of spring and autumn, the gelatine dries

quick enough in the air, but when the weather is warm and damp, the

gelatine, drying very slowly, may be so softened as to run off, or to

produce an entirely objectionable reticulation, or the defects above

mentioned. This may be avoided by drying it pinned up in a box, or a

closet, over quick-lime.



When dry, the tissue is generally wrinkled, brittle, breaks easily in

handling and cannot be laid flat on the cliche; but by holding it over a

basin of boiling water, the steam in a few moments rendering it

sufficiently pliable to lay it flat between glass plates, where it should

be kept under pressure until wanted for use.



The writer always dries the tissue in the following manner, which he

devised about sixteen years ago.(27) And not only the least trace of

reticulation is avoided, but the tissue, drying quite flat, lies in

perfect contact with the negative, which is quite important to obtain

proofs exactly sharp all over.



A clean glass plate is rubbed with talc, or, which the writer prefers,

flowed with a solution of(28)

Yellow wax, pure 1 part

Benzine, pure 100 parts



then strongly heated, allowed to cool and rubbed clean (apparently) with a

piece of flannel. After once more repeating this operation the plate is

coated with the following plain collodion:(29)



Ether, conc. 250 parts, in volume

Alcohol, 95 deg 250 parts, in volume

Pyroxyline 3 parts



When the film is set, the plate is immersed in filtered water until

greasiness has disappeared, when on its removal from the bichromate bath

the tissue is laid, without draining, upon it and pressed into contact

with the squeegee to remove the excess of liquid and, with it, the air

bubbles interposited. The tissue is then allowed to dry in the air on the

collodionized plate in the cold season, or, when the weather is warm and

damp, in a box in the bottom of which is placed a quantity of quicklime in

earthen dishes. When dry, the plates are placed one upon another, wrapped

in paper and kept in a dry place. When wanted for use the tissue is

stripped off and will be found quite flat with a beautiful surface to

print upon.



One should avoid to keep the sensitized tissue in a moist and warm

atmosphere, for in less than ten hours it becomes insoluble even in

complete darkness. It should neither be kept in the air contaminated with

gaseous reductive matters, such as the products of the combustion of coal

gas and petroleum, sulphydric or sulphurous emanations from any source,

the fumes of turpentine oil, etc., which, by reducing the chromic salt,

cause the insolubilization of gelatine, prevent the print to adhere on the

support or the clearing of the image, which may even refuse to develop.



The sensitive tissue keeps well for three or four weeks in cool and dry

weather, and no more than eight or ten days in summer unless well

desiccated and kept in a preservative box. If kept too long the image

cannot be developed.



The Photometer.--The time of exposure is regulated by means of a

photometer. Of all the photometers which have been devised for that

purpose we do not know any one more practical than that suggested in 1876

by Mr. J. Loeffler, of Staten Island. It is made as follows: On a strip of

a thin glass plate, 6x2 inches, make four or five negatives, 11/2x11/4 inch,

exposing each one exactly for the same period and developing in the usual

manner, but without any intensification whatever. It is even advisable to

reduce the intensity if they were opaque. Fix, etc., and apply a good

hard varnish. Now cover the back of these negatives with strips of

vegetable paper or transparent celluloid, or, better, of thin sheets of

mica, in such a manner as there be one thickness on the second negative,

two on the third, three on the fourth, etc., leaving the first one

uncovered. Then place on the whole a glass plate of the same size as the

first and border like a passe-partout.



The Negatives.--For the carbon process the negatives should be intenser

than those intended for printing out on silver paper. However, good

proofs may be obtained from any negatives, so to say, by varying the

strength of the bichromate solution, as, also, by using the tissue

freshly sensitized for weak negatives, in order to obtain vigor, and for

strong negatives, the tissue two or three days after its preparation,

when it yields better half tones. Printing dodges are also resorted to.

That the most commonly employed consists to varnish the back of the

negatives with a matt varnish, or to stretch on the same a sheet of

mineral paper upon which the retouches are made by rubbing graphite,

chrome yellow, pink or blue colors to strengthen the shadows or the

whites, as the case requires. As a rule, it is advantageous to cover the

printing frame with tissue paper, whatever be the quality of the

negatives.



The negatives should be bordered with deep yellow or orange-red paper to

form what is termed a "safe edge" upon which should rest the tissue in

order to prevent the margin from being insolubilized by the reductive

action of light. If this precaution were neglected it would be impossible

to strip off the paper without tearing the proof when the tissue is

applied on the support upon which the image is to be developed.



Before exposing it is advisable to ascertain what the printing qualities

of the negative are by making on silvered paper a proof of it--not

over-printed--and another of the photometer, both being exposed at the

same time and for the same period. This done, compare the proof from the

negative cliche with those of the photometer, and mark the negative with

the number of that of the photometer to which it corresponds, stating the

shade of the proof next to it; for example: No. 2; No. 3 faint, or

commences to appear, etc. This No. 2 and the observation will indicate

the intensity of the negative and serve as a guide for printing on the

tissue, since, as before explained, the silver paper is practically of the

same sensitiveness as the tissue prepared for negatives of the ordinary

intensity.



Exposure.--To print, the tissue is laid over the negative, taking care

that it covers the safe edge, and a strip of silvered paper placed in the

photometer, then both the printing frame and the photometer are exposed to

light side by side.



Unless the negative be weak, when more vigor is obtained by exposing in

sunshine, the printing should be done in the shade. It is a well-known

fact that the part of the bichromated film corresponding to the half

tones in the lights are not sufficiently impressed in comparison to the

blacks while impressed in direct sun's light in this as well as in the

collotype, photogravure and other processes with the chromic salts,

because the luminous action through the bare glass, or nearly so, which in

the negative represent the shadows and half blacks, is more energetic in

proportion than through the other parts, from which it results that these

parts being most acted on are made deeply insoluble through the thickness

of the film, and then require to be cleared by a treatment with water at a

higher temperature than the parts representing the half tints in the

lights of the picture, which are but superficially and slightly insoluble,

can stand.



From time to time during the exposure the print in the photometer is

examined, and when a certain picture is printed to a certain shade, or

when the one next by commences to appear or is faintly printed, etc., the

exposure of the tissue is sufficient. This, as the reader has already

inferred, is a matter of experience, the guide being the knowledge of the

intensity negative tested as above explained.



Development.--The carbon prints are developed either on a sheet of paper

upon which it should remain (single or simple transfer), or on a provisory

support to be afterwards transferred on paper or any other material

(double transfer).



Simple Transfer.--This process is quite simple: The impressed tissue and

a sheet of paper coated with alumed (insoluble) gelatine are immersed face

to face in cold water, and when the tissue is softened both are removed,

one superposed on the other, and the whole, being placed on a glass plate

and covered with a thin oil cloth, is firmly pressed into contact with the

squeegee. The rationale of applying under water the tissue on the

gelatinized paper is to avoid the interposition of air bubbles.



To operate by simple transfer the tissue should be impressed under a

reversed negative. The reason is obvious.



Double Transfer.--By this method the carbon prints are generally

developed on porcelain or opal plates, which more easily than glass plates

permit one to follow the progress of the development and to retouch the

imperfections before transferring the picture on paper.



In order that the image does not adhere on the provisory support a little

of the following mixture is spread over the plate, which is then pretty

strongly heated, and, when it has cooled down, polished lightly with a

piece of white flannel to obtain a very thin and even layer free from

striae. If the plate has not been used before for the purpose in question,

it should be waxed a second time in the same manner:



Yellow wax 4 parts

Rosin 1 part

Turpentine or benzine 250 parts



The plates can be developed on the plates so waxed, but for "full gloss,"

that is, for enameled pictures, a film of collodion is applied on the

plates, which then, instead of being waxed, should to be simply flowed

with a solution of India rubber 1 to 100 of benzole:



Ether 250 parts

Alcohol 250 parts

Castor oil 1 part

Pyroxyline 5 to 6 parts



When the plate is coated and the collodion film set, it is immersed in

water until greasiness has disappeared and wanted for use. Then the

tissue, previously soaked in water, is applied upon it (taking care to

avoid air bubbles) and squeezed, lightly at first, with some force

afterwards, to insure a perfect contact.



Zinc plates are also employed as provisory supports instead of glass, opal

or porcelain plates. The modus operandi is exactly the same.(30) The

plates should be well planed, free from scratches, etc., and well polished

to obtain glossy pictures without one having recourse to a film of

collodion. For matt pictures, i.e., without gloss whatever, the plate

should be finely granulated, and when waxing a very light pressure should

be exerted to remove the excess of wax, else it might be quite impossible

to strip off the picture in transferring on paper.



For double transfer on biscuits, objects in alabaster, porcelain, wood,

any even or curved rigid materials, flexible supports are employed to

develop the pictures. These supports are prepared by fastening albumen

paper on a board and evenly brushing over the following hot compound,

filtered through flannel, which, when dry, is polished with a cloth:

Stearine 15 parts

Rosin 3 parts

Alcohol 100 parts



The flexible supports should be waxed, then collodionized for full gloss,

as the glass, porcelain and metallic plates.



Another method which the writer recommends is the following, due to Mr.

Swan: Immerse a sheet of paper in a solution of India rubber, 4:100 of

benzole, and let dry, which requires a few minutes. This is the flexible

support. Then after exposure, brush over the India rubber solution on the

carbon tissue, apply upon it the support when the benzole is evaporated,

and pass the whole under a rolling press to secure adhesion, then develop.

To transfer, soak the proof in tepid water, apply it on the material

prepared, as it will be explained further on, and when dry, imbue the

support from the back with benzole, to soften the India rubber, and strip.



To dispense with a rolling press, the proof may be developed on lacquered

vegetable paper prepared by immersion in a solution of 10 parts of red

shellac in 100 parts of alcohol. After developing the proof is coated

with alumed gelatine, and when dry transferred as usual. To strip off it

suffices to imbue the paper with alcohol in order to dissolve the shellac.



When the picture must be transferred on small spaces or on small objects

the most simple method--the most effective, perhaps--is the following,

devised some years ago by the writer and now employed for the ornaments of

"articles de Paris:" Prepare the provisory support as usual, but with a

thicker film of collodion; then, after developing and coloring, if

necessary, the picture is coated with gelatine, to which may be added some

zinc white or other colored substance to form a ground. This dry, strip

off, immerse the pellicle in water to soften the gelatine and transfer on

the material collodion side up.



The proofs should be developed within three or four hours after

insolation, for the luminons action continues pretty actively in the dark,

and this for a long time; thus: a proof rightly exposed in the morning

behaves as one over-exposed if developed in the evening, and after a

certain period either can not be developed or refuses to adhere on the

support. However, the proofs can be kept for three weeks, may be more,

before development, if the soluble bichromate be washed off, the tissue

sponged and dried rapidly in the warm season. This capital improvement is

due to Mr. Charles Brasseur.



It has been said that before being applied on the support the proof should

be immersed in water to soften the tissue. The time which it should be

allowed to absorb water has an importance which must not be neglected. If

it do not remain long enough to be soaked through, small invisible air

bubbles are formed on its surface, and interposing themselves between the

image and the support, form minute, brilliant, silver-like spots on the

finished picture; and, if the temperature of the water is above 20 deg. C.

(68 deg. Fahr.), the image will be more or less reticulated. The

temperature depends a good deal of the softness of the gelatine; 15 deg.

C. (59 deg. Fahr.) is safe, except, however, when the thermometer is in

the thirtieths (90th Fahr.), when the water should be cooled down a few

degrees lower, but not at the melting ice temperature, for then the proof

would not adhere well. As a rule, the tissue should remain in the cold

water until it becomes flat and shows a tendency to curl up. It is at

this very moment that it should be squeezed on the support.



The proofs should not be developed immediately after transferring. The

adherence is greater and the pictures finer and devoid of defects when the

development is made half an hour, and even an hour, after. If developed

too soon the picture will be partly, and even entirely, washed off.

Hence, a number of transfers can be prepared beforehand, placing them,

face to face one upon another, in order that the tissue does not dry,

which is quite essential.



To develop, the plate, with the tissue adhering to it, is placed in water

heated to 30 deg. C. (80 deg. Fahr.), where it is left rocking the tray

occasionally until the paper rises up by itself at the corners, when

taking hold of it by one corner, it is stripped off, leaving behind the

image buried in soluble gelatine. Should the paper offer any resistance

whatever, the gelatine should be allowed to become more soluble by

increasing the temperature of the water, or by a longer immersion. There

is, in fact, no objection to this. The plate--and that is a good

method--can be placed in an upright position in a tin box, made ad hoc, and

left therein in warm water until the paper detaches itself and the image

is partly developed and the bichromate washed off. This done, the plate

is held in an inclined position on a tray filled with water at 35 deg. C.

(95 deg. Fahr.), which is dashed with a wooden spoon on the image to clear

it from the non-acted-on gelatine. Presently one can judge whether the

exposure is right. If it is too short, the half tints in the shadows are

washed off, unless the negative be too intense, when a similar effect also

occurs in the whites. If it is too long, either the image is with

difficulty cleared or remains undeveloped. In the latter case, it is

recommended by some operators to increase the temperature of the

developing water to near the boiling point, and, for local clearing, to

pour it on. This we find objectionable, for the half tints are easily

washed off. A better process, when the picture can not be cleared by

water at 50 deg. (122 deg. Fahr.), or thereabout, is to use a solution of

common salt at 5 or 6 per cent. of slightly warm water.(31) It is even

preferable to finish the development in a tepid solution of potassium

sulpho-cyanide, 12:100. The dissolving action is long, but not only, as

said above, the half tints are best preserved, but blistering and local

washing-off are avoided.



After development the plate is rinsed under the tap, then flowed two or

three times with a solution of chrome alum at 1 per cent. of water, then



washed, and finally allowed to dry spontaneously.



It is objectionable to use a strong solution of alum, and in it to immerse

the plate for any length of time; the gelatine is considerably

hardened--which is not necessary--and more liable to crack by time in being

thoroughly desiccated. We discard the common alum which we found liable

to produce a slight reticulation.



Two defects are complained of by the beginners, viz., the want of

adherence of the deep blacks, and, especially, the isolated and fine lines

when the picture is a reproduction of an engraving, a drawing, etc., and

the liability in half tone pictures of the delicate details being washed

out. The first defects are avoided by pouring a solution of boric acid on

the transitory support before applying the tissue and developing at a low

temperature with salted water. The second from an imperfect knowledge of

the properties of gelatine acted on by light in presence of a salt of

chromic acid. One should bear in mind that the degree of solubility of

gelatine so acted on, as also its degree of impermeability--which is

important in certain processes of photogravure--is proportionate to the

degree of insolation; thus, when not impressed, bichromated gelatine

dissolves in water heated to about from 25 to 30 deg. C. (77 to 80 deg.

Fahr.), and when acted on between 30 and 100 deg. C. (86 to 112 deg.

Fahr.), according as to the degree of insolation, that is, of reduction of

the chromic salt, the latter temperature being that of insolubility of the

parts the most acted on. The very delicate half tints do not, generally,

stand a temperature higher than 35 deg. C. (95 deg. Fahr.), and,

therefore, as the degree of insolubility of the various parts cannot be

ascertained, a priori, it is advisable during the development to increase

gradually the temperature of the water from this degree, and not to exceed

45 deg. C. (113 deg. Fahr.), in order to obtain the most perfect result

from a negative of good intensity. Indeed, by placing the supports on a

rack and immersing the whole in water heated to 30 to 35 deg. C. (86 to 95

deg. Fahr.), the image will clear up by itself to perfection in a certain

period. This method is excellent for proofs in lines. Those from the

grained negatives employed in photogravure are still more perfectly

developed in a tepid solution of potassium sulphocyanate, since the

impressions wholly consist of insoluble parts (the lines) and gelatine not

acted on.



Retouching.--The retouches are easily made. They should be done before

transferring when working by the double transfer process.



The transparent spots, and any parts which should be altered, are

retouched with the material of the tissue dissolved in warm water; the

whites are cleared with a scraper; and any parts which are not intense

enough, or which should be blended by the addition of half tints, are

worked on the proof--to which a tooth has been given by rubbing with

cuttle-fish powder--by means of a stump and an appropriate color, a mixture

of lamp-black and carmine, for example, in very fine powder.



The proofs can also be colored by chemical means (see further on), or with

water colors employed with a solution of chrome alum, 1 to 200 of water,

or gilt, silvered or bronzed with metallic powders applied with the

gilder's size thinned with turpentine on the proof previously coated with

a thin layer of alumed gelatine.



Second Transfer.--To transfer, a sheet of enameled or simple transfer

paper is immersed in tepid water until the gelatine is softened and feels

slippery to the fingers. The support is then placed under water at

ordinary temperatures--not under 16 deg. C. (60 deg. F.)--for two three

minutes, then rubbed with a camel brush to remove the air bubbles, which

might be formed on the surface of the image, when, without draining, the

gelatinized paper is laid upon it, covered with the thin oil cloth, and

pressed into contact with the squeegee, commencing in the center to the

sweep off the water, then repeating the operation for the other half, as

explained to apply the tissue on the provisory support. When the whole is

quite dry, which requires three or four hours, the edges are cut with a

penknife and the whole stripped off. It may happen that the proof is

covered with minute, silver-like brilliant spots, which are nothing else

than very small air bubbles interposited between the carbon proof and the

transfer paper. They are caused by the gelatine paper not having been

sufficiently softened or not laid on the proof with proper care. The

defect may also arise from the transfer paper coated with not sufficiently

thick gelatine.



To transfer on any rigid material, the proofs on flexible supports are

coated by floating on the following gelatine solution, then allowed to

dry, and, when wanted for use, immersed in tepid water to soften the

gelatine and secure adherence:



Gelatine 50 parts

Water 400 parts

Solution of chrome alum, 6 parts

4:100



Development on Absorbing Materials.--The development of carbon prints on

absorbent material--such as canvas and palettes to be painted in oil,

etc.--cannot be made in the ordinary manner on account of the impossibility

to eliminate entirely the chromic salt which tinges the material yellow.

To turn the difficulty, it suffices to wash off in several changes of cold

water all the unaltered bichromate from the prints on their removal from

the printing frame, and to proceed as usual, or the prints can be allowed

to dry and transferred at some future time.



Canvas should be prepared by brushing with a solution of aqueous ammonia

in alcohol, 5:20, to remove greasiness until the thread is apparent, and,

when dry, rubbed with sand to grain it--or to give a tooth, as it is

termed--then rubbed dry with a solution of soluble glass, 1 to 10 of

beer.(32)



Palettes should be rendered impervious, or nearly so, by flowing upon them

a solution of alumed gelatine, which is allowed to penetrate into the

pores of the wood and the excess scraped off when solidified, when the

surface may be whitened, if necessary, as for printing on wood box, q.v.



Opals, porcelain, or ivory should be prepared with the following

substratum:



Gelatine 50 parts

Water 400 parts

Chrome alum, 4:100 6 parts



Very fine carbon proofs having the appearance of pictures on opal plates

are made by transferring in the following manner, devised by the author:



Develop on the ground surface of a glass or porcelain plate, well waxed,

to obtain a matt picture, or in the ordinary manner for "full gloss," and

when the image is retouched or colored, apply a thin coating of gelatine,

let dry and coat with the following opaque collodion:



A. Ether, conc. 100 parts

Alcohol, 95 deg 90 parts

Pyroxyline 7 parts

B. White zinc in very 9 parts

fine powder

Castor oil 3 parts

Alcohol 10 parts



Grind in a mortar, adding ultramarine blue and carmine, or a little of any

suitable coloring matters, and mix to A. When the collodion is dry, which

requires a few hours, strip the whole or back with strong white or colored

paper before stripping. A solution of gelatine with glycerine, white zinc,

etc., may be substituted for collodion when the pictures are employed as

ornaments on wood, etc. Carbon prints on celluloid are now made for

similar purposes.

OPAL GELATINE SOLUTION

Gelatine 150 parts

Glycerine 15 parts

Zinc, white 40 parts

Water 600 parts



To which some coloring matters may be added according to taste. Grind the

white with the glycerine and a little water, mix to the gelatine dissolved

in the remainder of water, and filter through canvas. Apply the mixture

moderately hot, 30 deg. C. (86 deg. Fahr.)



Transparencies.--The transparencies are printed on a special tissue sold

under the name of "diapositive." It differs from the ordinary tissue in

this, that the mixture contains a greater quantity of the color matter,

India ink, which is ground exceedingly fine.



The proofs for transparencies should be printed deeper than those to be

seen by reflection, and developed on thin glass plates, free from any

defects, and coated with either one of the following substrata:



Soluble glass 5 parts

White of eggs 15 parts

Water 20 parts



The whole is beaten up to a thick froth and allowed to subside, when the

clear liquid is decanted, filtered through flannel and the glass plates

coated. The substratum should be allowed to dry for a few hours, and

rinsed under the tap before use.



The other substratum consists of



Gelatine 35 parts

Acetic acid, No. 8 250 parts

Alcohol, 95 deg 50 parts

Water 700 parts

Chrome alum, 4:100 60 parts



Dissolve the gelatine in the acid at a moderate heat, add afterwards the

alcohol and water, and lastly mix the chrome alum by small quantities at a

time.



These substrata are employed to avoid the peeling off of the image. To

prevent the entire desiccation of the gelatine, which is the cause of the

defect above alluded to, it is advisable to add glycerine to the washing

water after the image is cleared. Some operators recommend a coating of

flexible collodion, that is, prepared with castor oil, for the purpose in

question. We do not think that necessary when the transparencies are not

exposed to sunshine. If anything should be applied we would prefer the

encaustic.



Carbon transparencies are invaluable for reproducing negatives in the

original size by the same (carbon) process, or for enlarging by the

collodion or gelatine process. For these purposes they should be made on

the special red tissue manufactured by the Autotype Company, of London,

Eng. They can, however, be made on the ordinary tissues.



Whatever be the tissue employed, the transparencies for the reproduction

of negatives are seldom opaque enough, and should be intensified. This is

done by treating them with a very dilute solution of sodium permanganate,

which colors them olive green.



Transparencies for lantern slides, etc., are best colored with the

couleurs a l'albumine of L. Encausse, sold by J. Reygondaud, Paris

(France). They are transparent.(33)



Toning and Intensifying.--The carbon proofs can be toned and at the same

time intensified by reagents acting with chromic oxide.



The dyes or coloring matters precipitated are not opaque, and, as a

consequence, not objectionable for transparencies. The following

processes are the most employed:



Prepare three solutions as follows:



A. Ferric sulphate 5 parts

Water 100 parts

B. Sodium carbonate 2 parts

Water 100 parts

C. Gallic acid 5 parts

Water 100 parts



Dissolve the gallic acid in warm water. Filter each solution. They keep

well.



To tone, the plate is immersed for, say, ten minutes in A, then, after

rinsing slightly, it is placed in B for the same period, rinsed again and

flowed with C until the desired color is obtained. The tone is a splendid

purple black color. If a solution of pyrogallol be substituted to that of

gallic acid, the tone is green, and to a green bordering to black when a

solution of catechu is used, the catechu exerting at the same time a

tanning action on the gelatine. After toning, the plate should be

thoroughly washed.



A similar process consists to wet the plate under the tap, then to flow

over a mixture by about equal volumes of



A. Ferrous sulphate 5 parts

Acetic acid, No. 8 5 parts

Water 100 parts, filter

B. Gallic acid 5 parts

Water 100 parts



When toned, the plate is well washed, then flowed once with the alum

solution and again washed. The tone by this process easily turns to an

inky blue not very agreeable. The action should be stopped a little

before the desired color is obtained.



It sometimes happens that the image in drying intensifies more then

necessary. It can be cleared with a solution of oxalic or citric acid.



A brown sepia is obtained by toning first with potassium permanganate, 1

per cent. of water, then, after washing, with a solution of pyrogallol.

If gallic acid be used instead of pyrogallol, the tone is black. By this

process a great intensity is obtained. A dilute solution of ammonium

sulphide can be employed as a clearing agent.



Pyrogallol and silver nitrate give a warm black tone.



Potassium bichromate followed by silver nitrate form a brick-red

precipitate of some opacity.(34)



Chloride of nickel and potassium ferrocyanate produce a fine brown.



Lime water and alizarine dissolved in alcohol dye violet.



Alizarine and the caustic alkalies produce a variety of tints, from violet

to purple, according to the concentration of the solutions.



Lead acetate and alizarine in ammoniacal solution dye purple.



Potassium ferrocyanide and uranium nitrate produce a warm sepia tone. With

chloride of nickel the tone is brown.



Ammoniacal solution of coralline diluted with water gives carmine red.



Potassium bichromate and extract of indigo produce a fine greenish tone

suitable for landscapes.



Extract of indigo colors blue(35)



Some of these reactions can be applied to the printing processes with the

bichromates, etc. The paper should be coated with galatine. See the

Appendix.



Other colorations can be obtained with dyes in utilizing (as shown by

Persoz) chromous chromic oxide as a mordant: alizarine, Brazil and yellow

wood (morus tinctoria), Fustet (rhus cotinus), etc. The extent of this

work does not admit of describing the numerous processes which can be

employed; they will suggest themselves to the chemist.



The alkalies employed with the dyes should be employed in diluted

solutions, as being liable to produce reticulation. By applying the

coloring matters and the mordants thickened with a little starch, the

image can be colored with different colors. Lantern slides can be thus

colored with great ease.