Overview:
This 1891 treatise, “Photographic Reproduction Processes,” by P.C. Duchochois, delves into the world of photographic printing methods that don’t rely on silver salts. The text opens with Sir John Herschel’s groundbreaking research on iron salts, highlighting their sensitivity to light and demonstrating the foundation for many of the subsequent processes described.
Duchochois goes on to provide detailed instructions on various techniques, including cyanotype (blueprints), the “positive ferrotype” process known as cyanofer, the ferro-tannate (ink) process, the cuprotype (using uranium and copper salts), the aniline process, the primuline (diazotype) process, the uranotype, the platinotype, and the carbon process. Each process is explored with comprehensive explanations of the chemical reactions involved, detailed instructions for preparation, exposure, development, toning, and fixing, as well as helpful tips for avoiding common errors and achieving optimal results.
Key Findings:
- The text reveals the remarkable versatility of various chemical compounds beyond silver salts in photographic reproduction.
- The detailed descriptions offer valuable insights into the chemical processes involved, aiding in understanding the principles behind each method.
- The author highlights the importance of careful preparation and precise procedures for achieving high-quality and permanent prints.
Learning:
- Light as a Deoxidizing Agent: The text clarifies how light acts as a deoxidizing agent, reducing ferric salts to ferrous salts, which are then utilized to create visible images.
- Developing and Fixing: The reader learns about the distinct steps of developing and fixing photographic prints, highlighting the role of different chemicals in each stage.
- Chemical Processes: The book explains the intricate chemical reactions that underpin each printing process, providing a deeper understanding of the science behind photographic reproduction.
- Cyanotype Process: Duchochois elaborates on the cyanotype process (blueprints), detailing its simplicity and its widespread use in architectural and engineering fields.
- Cyanofer Process: The text explains how the cyanofer process utilizes gum arabic to create positive images from positive clichés, offering a unique approach to photographic printing.
- The Black (Ink) Process: The reader learns how the ferro-tannate process creates black prints through the interaction of iron salts and tannin or gallic acid, showcasing the versatility of this technique.
- Uranotype Process: The text explores the uranotype process, which uses uranium salts to create permanent prints with a unique brown-black tone.
- Platinotype Process: The book delves into the platinotype process, emphasizing its remarkable permanence and highlighting the use of platinum salts for creating high-quality prints.
- Carbon Process: The author provides an in-depth explanation of the carbon process, a complex technique that involves transferring an image from a sensitized tissue to a support using gelatine and various pigments.
Historical Context:
The book was published in 1891, a time of significant advancements in photography. The text reflects the ongoing pursuit of new and improved printing processes, especially those seeking to replace the less stable silver-based methods.
Facts:
- Cyanotype is Based on Herschel’s Research: The cyanotype process (blueprints), commonly known today, was originally devised by Sir John Herschel in 1840.
- Sunlight Reduces Iron Salts: Sunlight acts on ferric salts, reducing them to ferrous salts.
- Gum Arabic Enhances Cyanofer: Gum arabic is a key ingredient in the cyanofer process, making it a more reliable method for creating positive images.
- Tannin or Gallic Acid for Black Prints: The ferro-tannate process utilizes tannin or gallic acid to create black prints.
- Uranium Salts Produce Brown-Black: The uranotype process relies on uranium salts to produce a characteristic warm brown-black tone.
- Platinum Prints are Chemically Permanent: The platinotype process creates prints that consist entirely of platinum, rendering them highly durable and resistant to fading.
- Bitumen and Wax for Graphotypy: The graphotypy process utilizes a mixture of bitumen and wax to create a resist that allows for selective etching, resulting in a line-based image.
- Albumen Paper for Artigues Process: The Artigues process, an adaptation of the carbon process, typically uses albumenized paper as a base.
- Chromic Oxide Insoluble: Chromic oxide renders gelatine (or other organic substances) insoluble, which is a key principle behind the carbon process.
- Bichromate Solutions for Sensitizing: Potassium bichromate solutions are commonly used to sensitize tissues and papers in various photographic processes.
- Coating Tissues with Gelatine: Gelatine is the primary ingredient in carbon tissues, providing the base for holding pigments and reacting with light.
- Steam for Carbon Tissues: Steam is used to soften carbon tissues and make them pliable for printing.
- Photometer for Exposure: Photometers are used to determine the correct exposure time for different negatives and processes.
- Retouching Carbon Prints: Carbon prints can be retouched with pigment mixtures and a stump to enhance or blend areas.
- Coloring Carbon Prints: Carbon prints can be colored chemically using various dyes and mordants.
- Primuline is a Dye: Primuline is a dye that reacts with light and can be used to create photographic images.
- Nitrous Oxide Diazitizes Primuline: Nitrous oxide converts primuline into a diazotized form, making it sensitive to light.
- Different Developers for Different Colors: Different developers are used with primuline to create various colored prints.
- Tracing Process on Metal: The tracing process on metal utilizes a gelatine film to create a resist that protects certain areas of the metal from etching.
- Warm Water for Developing: Warm water is used to develop carbon prints, dissolving the gelatine that wasn’t exposed to light.
- Chrome Alum for Hardening: Chrome alum is used to harden the gelatine film in carbon prints, enhancing their durability.
- Graphite for Simple Transfer: Graphite is used to create an image on albumenized paper in the Artigues process, offering a simple and effective method for transferring the design.
Statistics:
- 6 to 1 Sensitivity Difference: Burnett’s research revealed a significant difference in sensitivity between uranic salts prepared with different acids. For example, the hydrofluate was six times less sensitive than the tartrate.
- 10-15 Days Keeping Quality: The ferro-tannate process using albumenized paper typically has a keeping quality of 10 to 15 days.
- 30 Seconds to 10 Minutes Exposure: The exposure time for the primuline process can range from 30 seconds to 10 minutes or more, depending on the light intensity.
- 20 Parts Ferric Oxalate per 100: The standard ferric oxalate solution used in platinotype processes should contain 20 parts of ferric oxalate per 100 parts of water.
- 80-85 deg. C. for Developer: The potassium oxalate developer used in platinotype should be heated to 80-85 deg. C. (176-184 deg. Fahr.).
- 2½ Parts Ammonium Bichromate: The Artigues process uses 2½ parts of ammonium bichromate in a specific solution for sensitizing albumen.
- 2 to 5 Per Cent. Bichromate Bath: The concentration of the bichromate bath used to sensitize carbon tissues varies from 2 to 5 per cent. of water.
- 15 deg. C. for Sensitizing: The bichromate bath used for carbon tissues should be cooled down to 15 deg. C. (59 deg. Fahr.) for optimal results.
- 12 to 15 Minutes Drying: The drying process for platinotype paper should take between 12 to 15 minutes to ensure proper development.
- 3 to 4 Weeks Keeping Quality: Sensitized carbon tissue typically has a keeping quality of 3 to 4 weeks in cool and dry weather.
- 100 deg. Fahr. for Coating: The gelatine mixture for carbon tissues is kept at 100 deg. Fahr. (38 deg. C.) during the coating process.
- 20 Sheets Coated in 15 Minutes: Harman’s method for coating carbon tissues allows for approximately 20 sheets to be coated in a quarter of an hour.
- 1 to 100 Benzole Solution: A solution of India rubber in benzole, 1 to 100, is used to coat plates for carbon print development.
- 10 to 12 Minutes Exposure: The exposure time for the Artigues process using albumenized paper can range from 2 minutes in sunshine to 8-10 minutes in the shade.
- 3 to 4 Hours for Drying: Carbon prints should be allowed to dry for 3 to 4 hours after transferring to ensure proper adherence.
- 30 to 35 deg. C. for Development: Carbon prints are typically developed in water heated to 30 to 35 deg. C. (86 to 95 deg. Fahr.).
Terms:
- Cliché: A printing plate or negative used to create photographic reproductions.
- Diapositive: A positive transparency used for printing, often made on glass.
- Non-Actinic: Not sensitive to light, meaning the material does not react with light in a way that would cause exposure.
- Insolation: The exposure of a photographic material to light.
- Developer: A chemical solution used to bring out a latent image.
- Fixer: A chemical solution used to make a photographic image permanent.
- Toning: A process that alters the color of a photographic image.
- Mordant: A substance that fixes a dye to a material, making it more permanent.
- Tournette: A rotating device used to spread a solution evenly on a metal plate.
- Substratum: A layer of material applied to a surface to promote adhesion or create a specific texture.
Examples:
- Cyanofer for Reproducing Plans: The cyanofer process, due to its ability to create positive images from positive clichés, is particularly useful for reproducing architectural and engineering plans.
- Aniline for Intricate Drawings: The aniline process offers a quick and effective way to reproduce designs with fine lines, making it suitable for intricate drawings.
- Primuline for Textile Printing: The diazotype process, utilizing primuline, has found application in textile printing, allowing for the creation of colorful patterns on fabrics.
- Uranotype for Photographic Prints: The uranotype process is praised for its ability to produce permanent prints with a distinctive brown-black tone, often used in the creation of photographic art.
- Platinotype for Fine Art Prints: The platinotype process is favored for its exceptional permanence and its ability to produce images with subtle tones and detail, making it a preferred technique for fine art printing.
- Carbon Process for High-Quality Reproductions: The carbon process, despite its complexity, is renowned for producing high-quality and detailed prints, often used for creating fine art reproductions and for specific printing applications.
- Artigues for Plans and Drawings: The Artigues process is especially suited for reproducing plans and drawings in lines due to its ability to produce black prints on a clean white ground.
- Graphotypy for Converting Images to Lines: The graphotypy process is used to convert images into line art, providing an alternative approach to engraving and creating artwork.
- Tracing Process for Metal Engraving: The tracing process on metal allows engravers to directly transfer images onto copper plates, saving time and effort in the engraving process.
- Carbon Printing on Canvas: The carbon process can be adapted for printing on canvas, allowing for the creation of unique art pieces and custom backgrounds for oil paintings.
Conclusion:
This comprehensive treatise on photographic reproduction processes without silver salts offers a fascinating glimpse into the evolution of photographic printing techniques in the late 19th century. Duchochois not only provides detailed instructions for each process, but also delves into the underlying chemical reactions, offering a deeper understanding of the science behind photographic reproduction. The text underscores the importance of careful preparation, precise execution, and a thorough knowledge of chemical interactions for achieving optimal results. The book serves as a valuable resource for anyone interested in the history of photography, the development of alternative printing processes, or the practice of historical printing techniques.