Photographic Enlargements





There are three kinds of photographic enlargements used as a basis for

crayon portraits, and, with a little experience, the student can

determine for himself which kind will prove the most satisfactory.



Free-hand crayons are made on Steinbach and other crayon papers,

without any photograph as a basis. Silver enlargements are made on

paper coated with a solution of chloride of silver, which the action of

the light reduces to salts of silver. This is the oldest form of

photography, and has been used since its introduction by Scheele in

1778. Silver enlargements are made by the aid of the sun (and are then

called solar enlargements) or they can be made with the electric light.



Platinum enlargements are a recent advance in photographic printing

with iron salts, the process which has been worked out and patented by

W. Willis, Jr., being a development of such printing. Its principle is

that a solution of ferrous oxalate in neutral potassium oxalate is

effective as a developer. A paper is coated with a solution of ferric

oxalate and platinum salts and then exposed behind a negative. It is

then floated in a hot solution of neutral potassium oxalate, when the

image is formed.



This process was first introduced by Mr. Willis in 1874, and he has

since made improvements. He claims that the platinotype paper does not

contain any animal sizing. The early experiments convinced him that the

paper upon which the image was to be printed would prove an important

factor, as all photographic paper contained animal sizing, which was

found to be antagonistic to platinum salts. The action of platinum

salts upon a paper containing animal sizing gave it a tint which no

amount of acid washing could remove. For the past nine years Mr. Willis

has had manufactured for his special use a Steinbach paper, free from

the animal sizing, and he also uses a cold developer, thereby causing

the paper to retain its original elasticity.



The chief points of difference between bromide enlargements and silver

or platinum enlargements are that, in the former, we have the sensitive

compound of silver suspended in a vehicle of gelatin, and, in the

latter, a thin coating of an aqueous solution of the sensitive salts.

In the former process, the image is not shown until the paper has been

developed in the bath, while in the latter, the image is shown upon the

paper when it is exposed to the light; so that, in the latter, the

image or picture has only to be fixed or made permanent, while in the

former, it is developed, then fixed. The gelatin bromide paper is

coated with a solution of gelatin, bromide of potassium and nitrate of

silver, developed with a solution of oxalate of potash, protosulphate

of iron, sulphuric acid and bromide of potassium and water, and fixed

with hyposulphate of soda. It is manufactured in America by E. and H.

T. Anthony & Co. and by the Eastman Dry Plate Company.





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