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Photographic printing
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Photographic printing is the process of producing a final image on paper for viewing, using chemically sensitized paper. The paper is exposed to a photographic negative, a positive transparency (or slide), or a digital image file projected using an enlarger or digital exposure unit such as a LightJet or Minilab printer. Alternatively, the negative or transparency may be placed atop the paper and directly exposed, creating a contact print. Digital photographs are commonly printed on plain paper, for example by a color printer, but this is not considered "photographic printing".[1]
Following exposure, the paper is processed to reveal and make permanent the latent image.
Printing on black-and-white paper
[edit]The process consists of four major steps, performed in a photographic darkroom or within an automated photo printing machine. These steps are:
- Exposure of the image onto the sensitized paper using a contact printer or enlarger;
- Processing of the latent image using the following chemical process:
- Development of the exposed image reduces the silver halide in the latent image to metallic silver;
- Stopping development by neutralising, diluting or removing the developing chemicals;
- Fixing the image by dissolving undeveloped silver halide from the light-sensitive emulsion:
- Washing thoroughly to remove processing chemicals protects the finished print from fading and deterioration.
Optionally, after fixing, the print is treated with a hypo clearing agent to ensure complete removal of the fixer, which would otherwise compromise the long term stability of the image. Prints can be chemically toned or hand coloured after processing.[2]
Panalure paper
[edit]Kodak Panalure is a panchromatic black-and-white photographic printing paper. Panalure was developed to facilitate the printing of full-tone black-and-white images from colour negatives – a difficult task with conventional orthochromatic papers due to the orange tint of the film base. Panalure also finds application as paper negatives in large format cameras. It is generally not suitable for conventional black-and-white printing, since it must be handled and developed in near-complete darkness.
Kodak has announced that it will no longer produce or sell this product.[when?] However, as of 2006[update], it is still available from various online retailers.
Silver mirroring
[edit]Silver mirroring, or "silvering", is a degradation process of old black-and white-photographic prints caused by conversion of the black silver oxide to silver metal. This results in a slightly bluish, reflective patch in the darkest part of a print or negative when examined in raking light. It often indicates improper storage of the prints.[3]
Printing on coloured paper
[edit]For more info see also: Chromogenic print
Colour papers require specific chemical processing in proprietary chemicals. Today's processes are called RA-4, which is for printing colour negatives, and Ilfochrome, for colour transparencies.
Printing from colour negatives
[edit]- Colour negatives are printed on RA-4 papers and produce a Type C print. These are essentially the same as colour negative films in that they consist of three emulsion layers, each sensitive to red, green and blue light. Upon processing, colour couplers produce cyan, magenta and yellow dyes, representing the true colours of the subject. The processing sequence is very similar to the C-41 process.[4]
- Rollei makes a film called 'Digibase 200 Pro' that is like a conventional C-41 film but it has no orange mask, allowing easy prints on black-and-white paper with a grade 2 or 3 variable contrast filter
Printing from colour transparencies
[edit]- Ilfochrome paper uses the dye destruction process to produce prints from positive transparencies. The colour dyes are incorporated into the paper and bleached during processing.[5] Ilfochrome, EP2 and Type R print papers and chemicals are no longer in production.
References
[edit]- ^ Breidenbach, Susan (2017-06-08). "Printed Matters". forbes.com. Small-Business Home-Office Technology Buyers Guide. Retrieved 2023-06-08.
At the high end of the market, the output from color inkjet printers can now give you almost the same results as the traditional photographic printing process that involves color separations.
- ^ Hughes, Andrew, Basic Darkroom Techniques: Developing B&W prints, archived from the original on 14 May 2008, retrieved 2 November 2008
- ^ Notch Code (2012): Forms of Photograph Degradation: Silver Mirroring. Archives and Special Collections Blog University Libraries, University of South Dakota; dated January 17, 2012. Accessed on 2020-05-05.
- ^ "Ever Wonder...How RA 4 Paper Works". Shutterbug. September 1, 2002.
- ^ "Ilfochrome". 13 January 2009.
See also
[edit]External links
[edit]Photographic printing
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History and Development
Early Innovations
In 1841, William Henry Fox Talbot introduced the calotype process, also known as talbotype, which utilized paper negatives to enable multiple positive prints from a single exposure. The process began with high-quality writing paper treated with silver nitrate and potassium iodide to create silver iodide sensitization, forming a negative image upon exposure in a camera. Positives, called salt paper prints, were produced by contact printing the negative onto paper coated with salt and silver nitrate, then fixing the image with sodium chloride or hypo. This negative-positive system represented a significant advancement over the unique images of daguerreotypes, allowing for reproduction.[1][7][8] The albumen print, developed by Louis Désiré Blanquart-Evrard in 1850, improved upon salted paper prints by providing greater sharpness and tonal range. Paper was coated with a solution of egg white (albumen) mixed with ammonium chloride, dried to create a glossy surface, and then sensitized with silver nitrate to form light-sensitive silver chloride. This coating allowed for finer detail in contact prints from glass or paper negatives, becoming the dominant printing method for the next several decades due to its clarity and archival stability.[9][10][11] A pivotal milestone came in 1851 with Frederick Scott Archer's wet collodion process, which shifted to glass plate negatives for enhanced resolution and detail. The glass was coated with collodion (a solution of nitrocellulose in ether and alcohol) mixed with potassium iodide and silver nitrate to form silver iodide, then exposed in the camera while still wet and developed immediately with a ferrous sulfate solution to prevent drying, which would render the plate insensitive. This requirement for on-site processing limited portability but enabled high-quality enlargements and prints, revolutionizing portrait and landscape photography.[12][13][14] By the 1860s, the establishment of commercial printing laboratories, exemplified by those of André-Adolphe-Eugène Disdéri in Paris, transformed photographic printing into a mass-production industry. Disdéri's 1854 patent for the carte-de-visite format—a small albumen print mounted on card stock—facilitated efficient contact printing from wet collodion negatives, producing multiple poses in a single session for affordable portraits. These studios employed teams of operators to handle the labor-intensive wet plate process, making photography accessible to the middle class and fueling a portraiture boom through standardized contact printing techniques.[15][16][17]Modern Advancements
The introduction of gelatin dry plates in 1871 by British physician and photographer Richard Leach Maddox marked a pivotal shift in photographic printing, replacing the cumbersome wet collodion process with a dry alternative that could be prepared in advance.[18] Maddox's method involved suspending silver bromide in a gelatin emulsion, which he detailed in a 1871 article in the British Journal of Photography, allowing for faster exposure times—reducing them from minutes to fractions of a second—and more stable printing without the need for immediate on-site development.[19] This innovation democratized photography by enabling field work without portable darkrooms, leading to widespread adoption of dry plate negatives for both professional and amateur printing by the 1880s.[18] The commercialization of gelatin silver bromide printing papers in the 1880s, pioneered by companies such as Eastman Dry Plate and Film Company (later Kodak), enabled projection enlarging from small negatives and provided finer grain and greater contrast control. These papers used silver bromide emulsions on baryta-coated supports, allowing for detailed, high-quality black-and-white prints that became the foundation of modern analog printing throughout the 20th century.[1] In the early 1900s, the development of panchromatic films enhanced spectral sensitivity, capturing a fuller range of colors and producing more accurate tonal reproductions in prints. Panchromatic emulsions, sensitive to the entire visible spectrum including red light, were first commercialized for still photographic plates around 1906, with Kodak introducing panchromatic negative film in 1913 to approximate human eye color response.[20] These advancements improved the fidelity of black-and-white prints, making them essential for portraiture and scientific documentation by the mid-20th century.[21] The launch of Kodak's Brownie camera in 1900 revolutionized amateur photographic printing by introducing affordable roll film and simplifying the process for everyday users. Priced at just $1, the box camera used 117 roll film, which users could advance and process at Kodak labs or home setups, sparking a boom in snapshot photography and home printing among non-professionals.[22] This accessibility, marketed with the slogan "You press the button, we do the rest," expanded the user base dramatically, with millions of Brownie units sold by the 1910s, fostering a culture of casual printing that relied on contact sheets and basic enlargements.[23] Post-1920s, the rise of electric enlargers transformed projection printing by providing consistent, controllable illumination indoors, moving away from daylight-dependent solar enlargers. Improvements in electric filament bulbs during the 1910s and 1920s enabled compact, reliable models suitable for home darkrooms, with widespread adoption by professionals and amateurs for larger, detailed prints from small negatives.[24] Complementing this, the invention of resin-coated (RC) photographic papers in the 1960s by companies like Kodak accelerated workflow with their polyethylene coating, which resisted water absorption and allowed prints to dry in minutes rather than hours, reducing processing time by up to 50% compared to fiber-based papers.[25] This made high-volume printing more efficient for both commercial labs and hobbyists.[26] Following World War II, automation in photographic printing advanced with innovations like the Beseler enlarger's evolution into professional models, enhancing precision and ease for darkroom operations. Beseler, entering the photography market in 1953 with the 45 Series enlarger, built on wartime audio-visual expertise to offer durable, adjustable systems that supported larger formats and integrated lighting for consistent results.[27] Concurrently, multigrade papers in the 1970s, exemplified by Ilford's updates to their variable contrast system, allowed contrast control through color filtration without changing papers, using dual emulsions sensitive to blue and green light for grades from 00 to 5.[28] Originally pioneered by Ilford in 1940, these papers saw refined RC versions in the 1970s that streamlined printing by enabling a single paper stock for diverse creative effects, significantly impacting darkroom efficiency.[29]Materials and Equipment
Photographic Papers
Photographic papers serve as the foundational substrate for creating prints in both black-and-white and color processes, consisting of a light-sensitive emulsion layered over a supportive base material. The emulsion typically comprises silver halide crystals suspended in gelatin, which capture light exposure to form a latent image during printing. These papers evolved historically from early albumen-based variants in the mid-19th century, where egg whites provided a glossy coating for silver salts on paper, to gelatin emulsions introduced in the 1880s that offered greater durability and sensitivity. By the 1960s, resin-coated (RC) papers emerged, featuring a polyethylene barrier that sealed the traditional paper core, enabling faster processing times and reduced water absorption during development, though initial versions raised concerns about long-term archival stability due to potential degradation of the plastic layers.[30][25][31] The core structure of modern photographic paper includes an emulsion layer containing silver halides—primarily silver bromide, chloride, or iodides—coated onto a base that ensures stability and image support. Fiber-based (FB) papers use a pure paper substrate, often with a baryta layer of barium sulfate in gelatin beneath the emulsion to provide a smooth, reflective white surface that enhances image brilliance and prevents chemical migration from the base. In contrast, RC papers incorporate thin polyethylene layers on both sides of the paper core, with the emulsion applied over the top coat; this waterproofing minimizes swelling during wet processing and allows for shorter washing times, typically under five minutes compared to over an hour for FB papers. Archival stability in both types depends on factors like fading resistance, where proper storage away from humidity and pollutants can preserve images for decades, though early RC formulations sometimes exhibited yellowing or delamination over time due to plasticizer migration.[32][33][34] Black-and-white photographic papers are categorized by their emulsion sensitivity and contrast control, with options suited for various printing needs. Graded papers feature fixed contrast levels, typically from grade 0 (soft) to 5 (hard), achieved through uniform silver halide crystal sizes in the emulsion; bromide papers, using pure silver bromide, produce high-contrast images with cool, neutral tones ideal for detailed landscapes. Chlorobromide emulsions, blending silver chloride and bromide, yield warmer, richer blacks and are common in variable contrast (VC) papers like Ilford Multigrade, which allow contrast adjustment via multigrade filters or developers containing benzotriazole to selectively harden specific spectral sensitivities. Orthochromatic emulsions, sensitive primarily to blue and green light, were prevalent in early 20th-century papers for contact printing under red safelights, though modern panchromatic variants extend sensitivity across the visible spectrum for more accurate tonal rendering from color negatives.[35][36][35] Color photographic papers operate on chromogenic principles, employing multilayered emulsions that form dyes during processing rather than metallic silver tones. These papers feature three superimposed emulsion layers, each sensitized to red, green, or blue light and containing dye couplers that react with oxidized developer to produce cyan, magenta, and yellow dyes, respectively, where silver halides are reduced. For negative-to-positive printing, types like Kodak Endura or Fuji CA use integrated couplers in the emulsion for subtractive color formation, enabling vibrant, continuous-tone reproductions with balanced hues when exposed through a color negative. The shift to RC bases in the 1970s improved handling for color papers, enhancing resistance to fading from environmental factors like ozone, though optimal archival life requires acid-free storage to prevent dye degradation over 100 years.[37][38][25] Paper surfaces influence perceived image quality through their interaction with reflected light, with choices ranging from matte to glossy affecting contrast, glare, and texture. Glossy surfaces provide a mirror-like finish that maximizes specular reflection, enhancing sharpness and color saturation by directing light directly back to the viewer, though this can introduce distracting glare in bright environments. Matte surfaces, conversely, scatter incident light diffusely due to their textured emulsion or coating, softening highlights and reducing contrast for a subtler, more forgiving rendition suitable for fine art prints where depth over brilliance is desired. Semi-matte or luster finishes strike a balance, offering moderate light diffusion that minimizes fingerprints while preserving detail, with scattering effects that maintain tonal gradations without the harshness of full gloss.[39][40]Chemicals and Processing Solutions
Photographic printing relies on a series of chemical solutions to develop latent images into visible prints by reducing exposed silver halides and stabilizing the emulsion. Developers initiate this process by converting exposed silver ions to metallic silver, while subsequent solutions halt development and remove unexposed halides to prevent further reaction and ensure archival stability.[41] In black-and-white printing, metol-hydroquinone (MQ) developers are widely used due to their superadditive properties, where metol provides fine grain and shadow detail, and hydroquinone enhances contrast and density in highlights. These developers typically include metol (N-methyl-p-aminophenol sulfate) at around 2 grams per liter and hydroquinone at 8 grams per liter, combined with sodium sulfite as a preservative, sodium carbonate as an alkali to maintain pH around 9-10 for optimal activity, and potassium bromide to restrain development and control fog. The pH balance is critical, as higher alkalinity increases contrast but can coarsen grain, while lower levels yield softer, finer results suitable for portraits.[42][43] For color negative printing, the C-41 process, introduced by Kodak in 1972, employs a chromogenic developer containing p-phenylenediamine derivatives that couple with oxidized color couplers to form magenta, cyan, and yellow dyes alongside silver development. This solution operates at a precise pH of approximately 10 and temperature of 38°C to ensure uniform dye formation without excessive silver buildup.[44][45] Stop baths neutralize residual developer to prevent continued reaction during fixing, typically consisting of 1.5-2% acetic acid solution, which rapidly lowers pH to approximately 2.6-2.7 and halts alkaline developer activity within 10-30 seconds. This acidic environment protonates the developer molecules, rendering them inactive and avoiding carryover that could degrade the fixer. Fixers remove unexposed and undeveloped silver halides to stabilize the image, with traditional formulas using sodium thiosulfate (commonly called hypo) at 200-250 grams per liter in an acidic medium to complex and dissolve silver ions without affecting the metallic silver image. Rapid fixers, developed for efficiency, incorporate ammonium thiosulfate at similar concentrations (around 150-200 grams per liter), which reacts 5-10 times faster due to the ammonium ions facilitating quicker complex formation, reducing fixing time from 5-10 minutes to 1-2 minutes. These are often buffered with acetic acid or sulfite to maintain pH near 6-7 and prevent sulfurization.[46][47] In color reversal printing for transparencies, such as the E-6 process, a bleach-fix (blix) solution combines bleaching and fixing in one step to remove metallic silver while revealing the dye image. This typically involves ferric ammonium EDTA or potassium ferricyanide as the oxidant to convert silver to soluble silver halides, paired with ammonium thiosulfate for rapid fixation, operating at pH 5.5-6.5 to avoid dye degradation. The blix shortens processing by eliminating separate bleach and fix baths, though it requires careful replenishment to prevent silver buildup that could stain the emulsion.[48][49] Many photographic chemicals pose health and environmental risks, necessitating proper handling and disposal. Hydroquinone, a key component in MQ and some color developers, is toxic by ingestion and inhalation, classified as a possible carcinogen with an oral LD50 of 330 mg/kg in rats, and can cause skin irritation or allergic dermatitis upon prolonged exposure. Post-1980s regulations under the U.S. Resource Conservation and Recovery Act (RCRA) require photo processing wastes containing silver, including spent fixers, to be managed as hazardous if exceeding 5 mg/L soluble silver threshold, with EPA guidelines mandating pretreatment or recycling to prevent environmental release of heavy metals and organics.[50][51][52]Darkroom Tools and Enlargers
A darkroom for analog photographic printing requires a carefully designed layout to separate dry and wet areas, ensuring efficient workflow while minimizing contamination and exposure risks. The dry area typically houses the enlarger and printing setup on a sturdy bench, while the wet area includes a sink or processing unit for chemical handling, with running water and proper drainage. Ventilation systems are essential to remove chemical fumes and maintain air quality, ideally changing the air five times per hour through lighttight vents or exhaust fans; this also helps control humidity at 45-50% to prevent mildew on equipment and paper.[53] Safelights provide illumination without fogging sensitive materials, using red filters for black-and-white processing to allow safe handling of panchromatic papers, and amber or orange filters for color work to avoid affecting color balance. Timers, often shelf-mounted near the processing trays, ensure precise exposure and development durations, typically wired directly to the enlarger circuit.[54] Enlargers serve as the core projection tool in the darkroom, projecting the negative image onto paper with adjustable magnification. Condenser enlargers use paired convex lenses to direct light evenly through the negative, producing higher contrast and sharper detail by minimizing light scatter, which enhances grain and highlights imperfections like dust. In contrast, diffusion enlargers employ a frosted glass or plastic diffuser to scatter light, yielding softer contrast and reduced visibility of scratches or dust, making them more forgiving for general use. Focus adjustment is achieved via bellows or a geared mechanism that raises or lowers the lens board relative to the negative plane, allowing precise sharpening across magnification ranges. Negative carriers, inserted between the light source and lens, hold film flat and mask unexposed areas; they accommodate formats from 35mm (using 50-63mm lenses) to 2¼x2¼-inch, 2¼x2¾-inch, and up to 4x5-inch sheets (requiring 135-160mm lenses for optimal coverage).[55] Processing trays and drums facilitate chemical immersion for development and fixing. Stainless steel trays, preferred for their durability, non-reactivity, and ease of cleaning, are used in manual processing setups, where prints are agitated by hand in developer, stop bath, and fixer solutions arranged in sequence. For color printing, motorized drums—such as those from Jobo systems—provide even, continuous agitation through rotation on a base unit, ensuring uniform processing with minimal chemistry volume (e.g., 300mL for 16x20-inch prints) and reducing streaking risks compared to tray methods.[56][57] Safelight filters, standardized in the Wratten series, are crucial to prevent unintended exposure; for instance, Wratten #1 (red) is suitable for blue-sensitive and orthochromatic papers, transmitting only safe wavelengths while blocking actinic light. In modern darkrooms, LED enlarger heads, introduced in the 2000s, offer energy efficiency by consuming far less power (e.g., 10W versus 150W for traditional halogen bulbs) and generating minimal heat, extending bulb life and stabilizing output for consistent exposures. Digital timers complement these advancements, featuring LED displays, moisture-resistant controls, and programmable intervals up to 9999 seconds, often with foot switches for hands-free operation during printing.[58][59][60]Black-and-White Printing Techniques
Contact Printing
Contact printing is a fundamental photographic technique that involves direct exposure of light-sensitive paper to a negative or transparency without magnification, producing a print of the same size as the original film. This method relies on placing the negative in intimate contact with the emulsion side of the paper, typically secured in a contact frame—a device consisting of a glass plate, backing board, and springs or hinges to ensure even pressure and prevent movement during exposure. The assembly is then exposed to ultraviolet (UV) light, such as sunlight or an artificial UV source, for durations typically ranging from 1 to 10 minutes, depending on the light intensity, negative density, and paper sensitivity; exposure is calculated by assessing the negative's density to achieve proper image formation.[13][61] The process begins with preparing the materials: the negative is positioned emulsion-to-emulsion on the paper in the contact frame, often with the glass covering the negative to maintain flatness. Exposure under UV light causes the image to form directly on the paper through photochemical reactions, without the need for an enlarger or additional optics. After exposure, the print is processed by washing in running water to remove unreacted chemicals, optionally toning with gold chloride for color and stability, and fixing in a sodium thiosulfate bath to halt further light sensitivity, followed by a final rinse. This straightforward workflow contrasts with development-heavy methods, as the image visibility builds during exposure itself.[13] Key materials include printing-out paper (POP), a historical emulsion of silver halides in gelatin or collodion that develops solely through light exposure without chemical developers, producing warm-toned prints that require fixing and washing post-exposure. POP, popular from the 1880s to the early 20th century, differs from modern contact papers, which are typically gelatin silver emulsions designed for shorter exposures under controlled UV lamps and subsequent chemical development, offering greater convenience and archival stability but less of the organic tonality of POP. Contact frames, often made of wood or aluminum with UV-transmissive glass, are essential for maintaining precise alignment and pressure.[13][62] Advantages of contact printing include its simplicity, requiring minimal equipment and no risk of optical distortion or loss of resolution from lenses, making it ideal for retaining the full detail of the negative. This fidelity is particularly valuable for large formats like 8x10 inches, where the print captures exquisite sharpness and tonal gradations directly from the film, avoiding the aberrations inherent in projection methods. The technique's directness also allows for high detail retention in alternative processes, preserving fine textures without enlargement-induced artifacts.[63][64] Historically, contact printing was central to early processes like calotypes, where William Henry Fox Talbot used salted paper in the 1840s to create the first negative-to-positive prints via sunlight exposure. It also underpinned cyanotypes, a non-silver process invented by John Herschel in 1842, involving ferric ammonium citrate and potassium ferricyanide to yield blue Prussian images after water rinsing. In the 1840s, botanist Anna Atkins employed cyanotype contact printing to document British algae and ferns, producing the pioneering photobook British Algae: Cyanotype Impressions (1843–1853), which used direct object placement or negatives for scientific illustration. Exposure in these early uses was gauged by visual inspection during sunlight exposure, based on the negative's density to balance highlights and shadows.[13][61][65] A notable variation is interpositive printing, where a positive transparency is contact-printed from an original negative using low-contrast film, often for duplicating originals or creating enlarged negatives for alternative processes; this intermediate step maintains size fidelity while allowing contrast adjustments through paper or film selection.[66]Projection Enlarging
Projection enlarging is a fundamental technique in black-and-white darkroom printing that allows photographers to create prints larger than the original negative by projecting the image through an enlarger onto sensitized photographic paper. This method enables precise control over magnification, focus, and exposure, facilitating creative adjustments to achieve desired tonal ranges and compositions. Unlike contact printing, which produces images at the same size as the negative, projection enlarging magnifies the image, making it essential for producing standard print sizes such as 8x10 inches from smaller film formats like 35mm.[67] The process begins with mounting the negative in a carrier, typically a glassless holder to minimize dust and scratches, and inserting it into the enlarger head. The enlarger height is then adjusted to achieve the desired magnification; for example, approximately a 7x to 8x enlargement ratio enlarges a 35mm negative (24x36 mm frame) to an 8x10 inch print area. Focusing is accomplished by projecting the image onto the baseboard and using a grain magnifier, which provides 8x to 10x magnification to critically align the negative's grain structure for sharpness across the print. Enlarger hardware, such as condenser or diffused light sources, ensures even illumination during this setup.[67][68][69] Suitable enlarging lenses are selected based on the film format, with a 50mm focal length standard for 35mm negatives to provide optimal coverage and minimal distortion at typical magnifications up to 10x. These lenses feature adjustable apertures, often from f/2.8 to f/22, where stopping down to f/8 or f/11 maximizes sharpness by increasing depth of field in the projected image.[69] Exposure is determined through test strips, where sections of paper are exposed progressively under the enlarger light—commonly in 2-second increments with a 75W incandescent bulb—to identify the optimal time for the highlights, midtones, and shadows. This iterative testing accounts for the inverse relationship between negative density and print exposure, ensuring balanced tonality before committing to a full sheet.[70][71] Once the base exposure is established, dodging and burning techniques allow localized control: dodging lightens areas by manually blocking light with hands, cards, or wires during the initial exposure, while burning darkens regions by providing additional exposure to those spots afterward, often for 10-50% of the total time depending on the adjustment needed. These manual interventions, performed under dim safelight, enable photographers to enhance contrast and draw attention to specific elements without altering the global exposure.[54][72] A common challenge in projection enlarging is dust spots appearing as dark blemishes on the print, caused by particles on the negative or carrier; these are mitigated by thorough cleaning with an anti-static brush and using anti-Newton ring glass in the carrier to flatten the film and prevent interference patterns while reducing dust adhesion.[73][54]Development and Fixing
After exposure, black-and-white photographic paper is immersed in a developer solution to reduce the exposed silver halide crystals to metallic silver, forming the visible image. Processing times vary by paper type: for resin-coated (RC) papers, development typically takes 1 to 2 minutes; for fiber-based papers, 2 to 3 minutes, both at a standard temperature of 20°C (68°F), with continuous or intermittent agitation to ensure even development across the print surface.[74][75] Agitation can be achieved by gently rocking trays containing the solution or using rotary drums for multiple prints, preventing uneven density from stagnant areas.[76] Development timing and temperature are critical for consistent results, as the chemical reaction rate approximately doubles for every 10°C rise above the standard, requiring shorter immersion times at higher temperatures to avoid overdevelopment and excessive contrast.[77] Conversely, cooler solutions demand longer times, though extremes should be avoided to maintain image quality; trays allow manual control, while drums provide automated agitation for efficiency.[78] Following development, the print is transferred to a stop bath, typically a 10- to 30-second immersion in a dilute acetic acid solution (around 1-2% concentration), to neutralize the developer and halt the reduction process abruptly.[75][74] This step prevents further image formation and minimizes chemical carryover into the next bath. The print is then fixed in a hypo (sodium thiosulfate) solution: 0.5 to 2 minutes for RC papers or 4 to 10 minutes for fiber-based papers, which dissolves the unexposed silver halides, rendering the image stable and insensitive to light.[76][75] Intermittent agitation during fixing ensures complete removal of halides, particularly important for fiber-base papers to achieve archival permanence. After fixing, thorough washing in running water removes residual fixer and byproducts, preventing long-term image degradation such as fading or yellowing: 2 to 10 minutes for RC papers or 20 to 60 minutes for fiber-based papers.[75][74] For fiber-base papers, extended washing is essential due to their absorbent emulsion, often aided by a hypo-clearing agent to shorten the process without compromising longevity; water temperature should remain above 5°C (41°F) to avoid emulsion damage.[74] Finally, the washed print is dried to preserve its finish and prevent defects. Air drying on mesh screens or racks takes 10 to 20 minutes at room temperature, allowing even evaporation, while heat dryers (up to 85°C or 185°F) speed the process but require low humidity to avoid curling.[74] Squeegees or wetting agents like photo-flo are used prior to drying to eliminate water spots and ensure a flat, streak-free surface.[75]Color Printing Techniques
Printing from Negatives
Color negative films processed using the C-41 method incorporate an orange mask to compensate for spectral imbalances in the dye-forming layers, particularly addressing unwanted absorptions in the green and red-sensitive emulsions, which helps achieve more accurate color reproduction during printing.[79] This mask typically results in a base density that contributes to an overall negative density range of approximately 0.2 to 2.0, allowing for the capture of a wide tonal scale from highlights to shadows.[80] The printing workflow begins with mounting the color negative in a color enlarger equipped with subtractive filters (cyan, magenta, and yellow) to control exposure and color balance. Initial filtration settings, such as 40 units magenta and 20 units yellow, are often used as a starting point to approximate the complementary corrections for the negative's orange mask, effectively balancing the cyan, magenta, and yellow dye densities in the print; adjustments are made based on test exposures to achieve neutral tones.[81] Following exposure onto chromogenic color paper, the print undergoes processing with RA-4 chemistry, a system introduced by Kodak in the 1980s for rapid access to color prints. The standard sequence involves development for 45 seconds at 35°C in the color developer to form the image dyes, followed by a 45-second bleach-fix step at the same temperature to remove silver halides, a 90-second water wash, and drying; this process yields stable, high-contrast prints suitable for color negative materials.[82] For manual tray processing, development times may extend to 90 seconds at slightly lower temperatures around 30°C to maintain consistent results.[83] Print evaluation relies on analyzing test strips or full proofs under standardized lighting to assess color balance, often using a color analyzer meter that measures light transmission through the negative's key areas—such as neutral grays or skin tones—to determine precise filtration adjustments, ensuring the final print renders grays without color casts.[84] A common issue in this workflow is color crossover, where unbalanced dye densities cause shifts like excessive magenta in highlights or green in shadows due to non-parallel characteristic curves in the negative layers, leading to overall color distortion; this is typically corrected through iterative test prints that refine filtration in increments of 10-20 units per color channel.[85]Printing from Transparencies
Photographic transparencies, also known as color reversal films or slides, are processed using the E-6 chromogenic reversal process, which produces a positive image directly on a transparent base without an integral color mask, distinguishing them from masked color negative films. These films are optimized for projection viewing, featuring high inherent contrast with a gamma value typically between 2.5 and 3.0 to ensure vibrant, saturated colors and sharp details under transmitted light.[86] Printing color prints from transparencies traditionally involves creating an interpositive on reversal film or paper as an intermediate step, which is then used to expose positive color paper such as Type C (chromogenic) paper.[87] Direct printing onto reversal-processed color paper is also possible, but requires significantly brighter exposures—typically 2 to 4 stops more than those used for color negatives—due to the higher optical density and lower latitude of transparencies.[88] Projection enlargers are employed to project the transparency image onto the paper, similar to methods used in negative printing but with adjusted lighting for the positive original.[89] The chemistry for reversal printing from transparencies adapts E-6 reversal baths to the paper, beginning with a first developer that selectively develops exposed silver halide grains to metallic silver, blackening those areas to form the basis for the positive image.[90] A reversal bath follows to fog unexposed areas, enabling subsequent development, after which a color developer couples oxidized developer with color couplers to form the cyan, magenta, and yellow dyes in the remaining emulsion layers.[91] Bleach and fixer steps then remove the silver, leaving the dye image on the positive paper.[91] Filtration during exposure is critical for color accuracy, as transparencies often exhibit warm color casts; cyan filters are commonly added to the enlarger head to cool the image by absorbing excess red and green light.[92] Precise control is achieved using transmission densitometers to measure red, green, and blue densities in the transparency, allowing for calculated filter packs that ensure neutral grays and balanced hues in the final print.[93] The development of Kodachrome slides in 1935 by Leopold Mannes and Leopold Godowsky at Eastman Kodak revolutionized color photography, offering unprecedented fine grain and color fidelity that made them ideal for projection but challenging for printing due to their high contrast and the need for exacting exposure and filtration to avoid muddy shadows or blocked highlights.[94][95]Color Balancing and Masking
In color photographic printing, achieving accurate color reproduction requires precise balancing to compensate for variations in film dyes, paper sensitivities, and light sources, often through filtration systems and masking techniques. Color head enlargers, commonly used in darkroom setups, employ additive red, green, and blue (RGB) light sources that are converted to subtractive cyan, magenta, and yellow (CMY) filtration via dichroic filters or LED arrays, allowing photographers to adjust exposure for each color channel independently. These systems typically feature dials calibrated in 0-200 units for fine-tuned control, enabling subtractive adjustments that reduce unwanted color casts by filtering out specific wavelengths from the enlarger's white light.[96][97] Masking methods further refine color accuracy and image sharpness during printing. Unsharp masks, created on glass or thin film substrates, involve contact-printing a low-contrast positive from the original negative and sandwiching it with the negative in the enlarger; this technique enhances edge contrast by locally boosting midtone and highlight transitions without affecting overall density, particularly useful for softening halos or improving definition in color prints. Dye masks integrated into color negatives address halation—light scatter causing unwanted glows around bright areas—by incorporating anti-halation dyes in the film's backing layer, which absorb stray light during exposure and are subsequently cleared in processing to prevent interference in printing. Additionally, these masks correct for spectral imperfections in subtractive dyes, reducing color crossover where one dye absorbs unintended wavelengths.[98][99][100] The color balancing process relies on iterative test prints to analyze and adjust red, green, and blue densities. Photographers expose small strips or step wedges on color paper under controlled filtration, then develop and evaluate them visually or with densitometers to measure optical density in each channel, aiming for a minimum density (D-min) of approximately 0.15 in the paper base to ensure neutral whites without excessive fogging. Adjustments are made by incrementing CMY filtration—typically in 5-10 unit steps—until the test print shows balanced neutrals and accurate hues, with multiple iterations often required to account for film batch variations or enlarger inconsistencies. This method, rooted in analog precision, minimizes trial-and-error in full-sized prints.[101] Early digital aids emerged in the 1970s to automate aspects of this process, with color analyzers and meters linking directly to enlarger controls for pre-scan analysis. Devices like the Beseler PM1A or Omega analyzers scanned negatives or transparencies to compute RGB densities, automatically setting filtration and exposure times via integrated timers, reducing manual balancing to a single setup step. These tools, often featuring photodiode sensors, represented a bridge between analog printing and computational assistance, improving consistency in professional labs.[102][103] Advanced color papers incorporate built-in masking for automatic correction, exemplified by integral tripack emulsions like Kodak Ektacolor RC paper. This multilayer structure embeds opaque masking layers—typically between the blue- and green-sensitive emulsions—to preemptively counter dye absorption issues during development, ensuring subtractive color formation yields truer hues without external masks or extensive filtration tweaks. Such designs simplify balancing for RA-4 processing by embedding corrections at the material level.[104]Alternative and Specialized Methods
Toning and Alternative Processes
Toning is a post-processing chemical treatment applied to black-and-white photographic prints after fixing to alter their color and enhance longevity. Sepia toning, which produces warm brown hues, involves first bleaching the print with potassium ferricyanide to oxidize the metallic silver, followed by immersion in a solution of thiourea and sodium hydroxide. This reaction converts the silver to silver sulfide, yielding the characteristic sepia tone while improving archival stability by making the image more resistant to environmental degradation. The process typically requires 5-10 minutes in the toning bath, depending on concentration and temperature, and is performed on fully developed and fixed prints to avoid uneven results.[7] Blue toning, another common method, utilizes potassium ferricyanide and ferric ammonium citrate to replace silver with Prussian blue (ferric ferrocyanide), creating cool cyan to deep blue shades. Applied after fixing, the toner is diluted (e.g., 1:1:22 ratio) and immersion time is limited to about 5 minutes for fiber-based papers to prevent over-toning. This treatment not only provides aesthetic contrast but also boosts archival stability, as the iron-based compound is less prone to fading than untreated silver images; a brief hypo fix can further enhance permanence.[105][7] Alternative processes encompass non-silver halide methods that rely on iron or other salts for image formation, often yielding unique artistic effects through contact printing. The cyanotype, invented by Sir John Herschel in 1842, uses a sensitizer of ferric ammonium citrate and potassium ferricyanide coated on paper, which upon UV exposure forms insoluble Prussian blue in proportion to light received. After development in water, the resulting blueprints exhibit a distinctive blue monochrome with simple, high-contrast aesthetics, prized for their simplicity and low toxicity.[106] Gum bichromate printing, developed in the mid-19th century, enables layered color images by combining gum arabic as a binder with pigments and a dichromate sensitizer (ammonium or potassium). Multiple emulsions, each with a different color separation negative (e.g., cyan, magenta, yellow), are coated sequentially on paper, exposed to UV, and developed in water; unexposed gum dissolves, leaving hardened pigmented layers that build depth and vibrancy. This process allows for extensive artistic control over tone and hue through pigment choice and layer registration. However, dichromates are highly toxic carcinogens, necessitating gloves, goggles, and local exhaust ventilation (at least 10 air changes per hour) to mitigate inhalation and skin exposure risks.[107][108] The Van Dyke brown process, an iron-silver technique derived from Herschel's 1842 argentotype, sensitizes paper with ferric ammonium citrate and tartaric acid alongside silver nitrate, producing warm brown tones upon development in sodium thiosulfate. For intensification and color shifts toward purplish-brown, gold chloride (1-2% solution) is added to the sensitizer or used in a post-toning bath with thiourea, enhancing image density without significant loss. This method yields prints with a soft, painterly quality reminiscent of 17th-century artist Anthony van Dyck's palette.[109] Platinum-palladium printing, patented by William Willis in 1873, represents a modern revival of a historically significant non-silver process, where iron oxalate sensitizes handmade or coated papers impregnated with platinum and palladium chlorides. UV exposure reduces the metals to form a neutral to warm black image with exceptional dynamic range—up to 12 stops—offering subtle tonal gradations and inherent archival permanence due to the noble metals' stability. Handmade papers enhance the process's tactile, fine-art appeal, distinguishing it from commercial silver prints.[110]Silver Mirroring and Specialty Papers
Silver mirroring is a toning technique applied to silver gelatin black-and-white prints to produce a reflective metallic sheen on the image surface, often resulting in iridescent colors such as reddish, bluish, greenish, golden, or bronze hues. This effect mimics the natural deterioration seen in aged photographs due to factors like acidity, humidity, and electrostatic forces, but is intentionally created through chemical processes to enhance artistic expression in alternative photography.[111] The process involves selectively depositing metallic silver on the print's surface, either in highlight or shadow areas, using alkaline solutions and halides to promote silver migration. Direct silver mirroring toning targets highlights and occurs before the fixing bath: the print is partially developed for 50 seconds to 2 minutes, then immersed in a toning solution of 10% potassium hydroxide (KOH) and 20% potassium thiocyanate (KSCN) mixed with developer for 1 to 3 minutes, followed by standard fixing and washing. Indirect silver mirroring toning affects shadows and takes place after fixing: the fixed print is bleached with a 5% copper(II) chloride (CuCl2) solution for 1 to 3 minutes, then re-toned in a solution of 0.4% sodium hydroxide (NaOH), 8% ammonia, and 2% developer in warm water, yielding a more pronounced metallic reflection in darker tones. Safety precautions, including gloves and ventilation, are essential due to the caustic nature of the chemicals involved.[111] This toning method revives discontinued commercial processes from earlier decades, allowing contemporary photographers to achieve vintage-like metallic effects on modern silver gelatin papers such as Ilford Multigrade RC Pearl. It is particularly valued in alternative processes for its ability to add depth and luminosity without altering the underlying silver image structure significantly, though over-toning can lead to uneven deposition or loss of detail.[111] Specialty papers in photographic printing refer to emulsion-coated substrates designed for silver gelatin processes, offering unique textures, finishes, and archival qualities beyond standard resin-coated (RC) or fiber-based options. These papers emerged historically to meet artistic and technical demands, with innovations like the baryta layer—introduced in 1866—providing a smooth, reflective base for enhanced image sharpness and tonal range in developing-out papers (DOP). Printing-out papers (POP), common from 1880 to 1940, represent an early specialty variant where the image forms directly under light exposure without chemical development, often on matte or glossy surfaces for contact printing applications.[32] Among modern specialty papers, fiber-based options like Ilford Multigrade FB Classic provide a traditional cotton rag substrate for deep blacks and subtle highlights, ideal for toning techniques including silver mirroring due to their absorbency and longevity. Resin-coated papers, pioneered by Kodak in 1968 with polyethylene lamination, facilitate rapid processing and are suited for high-volume printing, though they may exhibit less tonal gradation than fiber alternatives. Other specialized types include metallic papers with embedded metallic particles for enhanced sheen (produced until the 1970s), Gevaluxe papers featuring an electrostatic cellulosic microfiber coating for velvety texture (discontinued in the late 1950s), and baryta-less variants for cost-effective digital-analog hybrids. Liquid emulsion papers allow custom coating on non-traditional supports like ceramics or fabrics, expanding creative possibilities in alternative printing.[32][112] These specialty papers prioritize archival stability, with fiber-based types often toned with selenium or gold for protection against fading, as silver gelatin images are prone to degradation like mirroring if untoned. Selection depends on the desired aesthetic: glossy finishes amplify reflective effects in toning, while matte surfaces suit subtle, non-glare presentations. Manufacturers such as Ilford, Foma, and Bergger continue to produce these papers, ensuring compatibility with both enlarger-based analog workflows and digital exposure units.[32]Digital Integration in Analog Printing
One key aspect of digital integration in analog printing involves scanning traditional film negatives to create high-resolution digital files, known as digital intermediates, which can then be output via inkjet printers on specialized papers. Flatbed scanners like the Epson Perfection V700 or V850 are commonly used for this purpose, capturing negatives at resolutions up to 2400 DPI to preserve fine details from medium- and large-format films.[113] These scans, often saved as 16-bit grayscale TIFF files, serve as the bridge between analog capture and digital refinement, allowing for subsequent printing on baryta-based papers that mimic the texture and tonal depth of traditional silver gelatin prints.[114] Hybrid workflows further blend digital precision with analog enlargers by incorporating LED exposure units, which emerged prominently in the 2010s to replace halogen lamps and color filters. Devices such as the Heiland Splitgrade LED head provide split-grade control, enabling precise adjustments to contrast and exposure through blue and green LED channels without the need for physical filters, thus streamlining darkroom operations while maintaining compatibility with conventional enlargers.[115] This setup allows photographers to expose multigrade papers with digital timing and metering for consistent results across sessions.[116] Archival pigment inks, such as Epson's UltraChrome series, play a central role in simulating the appearance of darkroom prints during the inkjet output phase of hybrid processes. These inks deliver exceptional color fidelity, gloss uniformity, and scratch resistance, with fade resistance rated for over 400 years in framed displays, making them suitable for fine art reproductions that emulate traditional black-and-white tonality.[117] Color matching is achieved through ICC profiles tailored to specific printer-paper combinations, ensuring accurate translation of scanned negatives to output media like baryta or cotton rag.[118] Software tools enhance these integrations by emulating classic darkroom techniques digitally. In Adobe Photoshop, Curves adjustment layers allow for non-destructive dodging and burning, where separate layers are used to lighten highlights or darken shadows via masked edits, replicating manual enlarger manipulations with precise control over tonal ranges.[119] For large-format output, Raster Image Processor (RIP) software like ONYX Graphics optimizes file rendering, handling color management, nesting, and high-resolution rasterization to produce seamless prints from hybrid files.[120] The advantages of these digital integrations include the ability to generate unlimited editions from a single negative scan and perform iterative corrections without depleting analog materials, extending the life of original exposures. For instance, photographer Tim Layton employs this approach in his analog-digital hybrid workflow, scanning large-format negatives and applying digital toning in Photoshop to achieve selenium-like effects before printing on archival baryta paper, resulting in prints that rival traditional darkroom output in depth and longevity.[114]References
- https://psap.library.[illinois](/page/Illinois).edu/collection-id-guide/digitalprint