The carbon process, initially a black-and-white process using lampblack (carbon black), was invented by Alphonse Poitevin in 1855. The process was later adapted to color, through the use of pigments, by Louis Ducos du Hauron in 1868. Carbon printing remained commercially popular through the first half of the 20th century. A Carbro print is an assembly of three bichromated gelatin tissues, each pigmented with one of the primary subtractive colors, cyan, magenta, or yellow. The image on each tissue is formed as a result of a chemical reaction that occurs when the bichromated gelatin tissue is placed in contact with a silver bromide print. The silver bromide prints, each made from a black-and-white separation negative cause the tissues’ gelatin to harden in proportion to the density of the print. The unhardened gelatin is then washed away. When these tissues are placed in exact register onto a paper support, they combine to produce a full-color (tricolor) photograph. The Carbro process, patented in 1905 as the Ozobrome, was adapted from carbon printing techniques developed in the 1850s. Though monochromatic Carbro prints were made, this process is best-known through its vivid three-color images. Carbro prints are also noted for their image permanence.
In the photograph below (Lillian Gish on Sunday News cover 1942), one can notice the natural and vivid colors preserved after so many years.
Steps (methods are slightly different according to technician-artist):
- Measuring pigment, glycerin and gelatin in proportion and mix with cold water. I just use a kitchen blender to do the mix and works well.
- Put the container with mixed materials in the refrigerator and let it swell over night. Stainless steel bowls works great.
- Double boiler method to heat and dissolve gelatin at a temperature of 120 f with plastic wrap over the top to keep the heat in, and keep the bacteria and other matter out. Stir constantly to reduce the bubble and air.
- After the gelatin cools off, strain the gel with a very fine strainer
- Put double weight silver paper in fixer, wash and dry. Before coating, I will presoak this paper again in warm water of 110 f
- I use a twenty by thirty sheet of glass set on a frame that I can level the glass and keep the gelatin in place. I will heat the glass with hot water by just spraying it over the top of the glass. Take the presoaked receiver sheet (the fixed out and washed photo paper) from the warm water, lay it on the warm glass and get rid of all the excess water with a rubber squeeze. I use 450ml graduates to contain the warm gel and to pour the gel on the paper. Starting a stream close to the edge and spiraling toward the center, then I put the gel back in the warm water to stay warm and spread the gel with my fingers till it al comes together in a solid sheet. If you don’t lift your fingers when coating, you don’t get bubbles.
- Now let the gel cool, I use a fan in the darkroom or run cold water under the glass, when it’s solid, hang it up to dry and the next day you can start to work. It takes about 50 ml to coat an 11×14 sheet.
- The silver gelatin print needs to presoak for about fifteen minutes in cool water lay it on the glass sheet, removing all excess water, using the rubber squeeze and even a paper towel if necessary.
- Soak the gelatin coated sheet in the sensitizer for about three minutes at 68 degrees f or until it lie flat, a lot will depend on the humidity of the air where you are working.
- On a 100% leveled surface, lay the silver print at the bottom and face up. Remove the sensitized sheet from the chemical bath and drain well, face down. Put the two together and make sure they have a good contact. If they slip when bringing them into contact, you will get a blurred image. It’s a good idea to have registration pins place in the board or sheet you are working on and hole to match on both the tissue and the print you are using. I then place old newspapers over the sandwich and a sheet of glass on top of that for weight to be sure the contact is good. Let it set for 20 minutes.
- Removing the glass, newspaper register and finally the gel and print paper. Taking the gel and print paper apart, lay the gel paper face down on a fixed silver photo paper and registered for another 20 minutes. The image from the receiving paper will be transferred to the fixed double weight silver paper. The paper with silver, the gel hardens while the area without silver, gel washed away.
- Put them in a warm water of 110 f and let them separate. It will take 5 to 10 minutes to come apart.
- Discard the gel-receiving sheet, now you agate softly the fixed paper with transferred Carbro image in the warm water till the unhardened gel washed away.
- Hanging up and let it dry totally.
- Mix glycerin in cold water, and soak the Carbro imaged paper for a hour which will saturate the pigment and flatten the print.
- Dry the print again.
Example: In below illustration, one can notice the difference between frames (B/W scan) due to color separation on each layer. The “left” Lillian Gish looks almost like a different person. Published on few social media networks and blogs this photo (part of carbro process) was labeled as “Helen Hayes”.
It is very doubtful whether any process so completely like the requirements of the artistic photographer as does the carbon process. Its long scale, its deepest shadows combine to render it the most perfect of photographic printing methods. Carbon printing as we know it today is based on the fact that a mixture of gelatin with as chromic salt is gradually hardened and rendered insoluble on exposure to light or chemistry. If, therefore, paper is coated with such a mixture of sensitized gelatin, containing any permanent pigment – carbon was originally used – and if this paper is placed underneath a negative and exposed to actinic light, we shall have a positive image formed consisting of soluble and insoluble gelatin; insoluble in exact proportion as the light has reached the surface of the pigment compound. Development consists in washing away with hot water those portions of gelatin which the light has not affected sufficiently to render insoluble. I would urge every serious photographer to master this fascinating process, for till he has done so, he must be unaware of many of the possibilities of his art. Carbro printing is basically a transfer process. Since there is none transfer paper exists, you have to hand coat you own paper and mix your own chemistry. Besides you can print black and white pictures.
A carbon print is a photographic print with an image consisting of pigmented gelatin, rather than of silver or other metallic particles suspended in a uniform layer of gelatin, as in typical black-and-white prints, or of chromogenic dyes, as in typical photographic color prints. In the original version of the printing process, carbon tissue (a temporary support sheet coated with a layer of gelatin mixed with a pigment—originally carbon black, from which the name derives) is bathed in a potassium dichromate sensitizing solution, dried, then exposed to strong ultraviolet light through a photographic negative, hardening the gelatin in proportion to the amount of light reaching it. The tissue is then developed by treatment with warm water, which dissolves the unhardened gelatin. The resulting pigment image is physically transferred to a final support surface, either directly or indirectly. In an important early 20th century variation of the process, known as carbro (carbon-bromide) printing, contact with a conventional silver bromide paper print, rather than exposure to light, was used to selectively harden the gelatin. A wide variety of colored pigments can be used instead of carbon black. The process can produce images of very high quality which are exceptionally resistant to fading and other deterioration. It was developed in the mid-19th century in response to concerns about the fading of early types of silver-based black-and-white prints, which was already becoming apparent within a relatively few years of their introduction.
*** Rumors – “Carbro” was the idea that inspired the scientists who engineered the CCD system for modern digital filming cameras, the chemical compounds (cyan-magenta-yellow) being replaced by electronic sensors with the same task – to separate the colors in RGB base (red-green-blue).