Print Processing Chemistry

Print chemistry transforms exposed paper into a permanent image. Understanding your chemicals—what they do, how to use them, and how to maintain them—gives you consistent results and creative control over image tone.

This guide covers print developers, stop baths, fixers, washing, and drying.

Print Chemistry Overview

The wet processing sequence for prints mirrors film development:

1. Developer — Converts exposed silver halides to metallic silver (the image)
2. Stop bath — Halts development by neutralising the developer
3. Fixer — Removes unexposed silver halides, making the image permanent
4. Wash — Removes fixer and dissolved silver from the print
5. Dry — Final step before the print is complete

Each step has specific requirements and affects the final print.

Print Developers

Print developers are formulated differently from film developers. They work at higher concentrations, produce higher contrast, and are designed for visual inspection during development.

How Print Development Works

Unlike film (developed in total darkness), print development happens under safelight where you can watch the image emerge. The developer converts light-struck silver halides to black metallic silver.

Standard development: 60-90 seconds at 20°C (68°F)

The entire image should appear within the first 30 seconds; the remaining time builds maximum density and proper contrast.

Developer Types

Neutral-Tone Developers

Produce clean, neutral blacks. The standard choice for most work.

Ilford Multigrade Developer:

• Dilution: 1+9 (stock + water)
• Time: 60 seconds at 20°C
• Capacity: ~15 8×10 prints per litre working solution
• The default choice for Ilford papers

Kodak Dektol:

• Dilution: 1+2 (stock + water)
• Time: 60-90 seconds at 20°C
• Capacity: ~20 8×10 prints per litre
• Classic American developer, slightly cooler tone than Multigrade

Formulary 130:

• Neutral developer available in powder form
• Similar characteristics to Dektol

Warm-Tone Developers

Produce brown-black tones, especially on warm-tone papers.

Ilford Warmtone Developer:

• Dilution: 1+9 (standard) or 1+14 (warmer)
• Time: 90-120 seconds for maximum warmth
• Higher dilution and longer time = warmer tones
• Best results on warm-base papers

Ethol LPD:

• Variable dilution: 1+2 (neutral) to 1+4 (warm)
• Versatile—can produce neutral or warm depending on dilution
• Long tray life

Agfa/Adox Neutol WA:

• Dedicated warm-tone developer
• Produces noticeably warmer tones than neutral developers

Cold-Tone Developers

Less common, producing blue-black tones.

Edwal G (discontinued, formulas exist):

• Produces cool, blue-black tones
• Mostly achieved today through paper choice and toning

Developer Temperature

Standard temperature is 20°C (68°F).

Warmer developer (22-24°C):

• Faster development
• Can produce warmer tones on some papers
• Shorter tray life

Cooler developer (18°C):

• Slower development
• Longer development times needed
• Potentially cooler tones

Consistency matters more than exact temperature. Pick a working temperature and maintain it throughout the session.

Developer Capacity and Exhaustion

Developer weakens with use. Signs of exhaustion:

• Development takes longer to reach full density
• Blacks become grey/muddy
• Contrast decreases
• Colour shifts to yellow/brown

Capacity guidelines:

• 15-20 8×10 prints per litre of working solution
• Fewer for larger prints
• Fresh developer for critical work

Tray life:

• Working solution oxidises in open trays
• Discard after 4-8 hours, even if unused
• Cover trays between sessions doesn't fully prevent oxidation

Replenishment

Some developers can be replenished—adding fresh concentrate to maintain strength. This is more common in high-volume production than personal darkrooms.

For most photographers: mix fresh working solution for each session rather than replenishing.

Stop Bath

Stop bath halts development by neutralising the alkaline developer with acid.

Acid Stop vs Water Stop

Acid stop bath:

• Instant, complete stop
• Extends fixer life
• Contains indicator to show exhaustion
• Standard practice

Water stop:

• Works but slower
• Developer carried into fixer exhausts it faster
• Acceptable for RC paper and casual work
• Some printers prefer it for warm-tone papers (acid can cool the tone slightly)

Indicator Stop Baths

Most stop baths contain an indicator dye that changes colour when exhausted:

• Fresh: Yellow or clear (depending on brand)
• Exhausted: Purple/blue

Common stop baths:

• Ilfostop: Yellow when fresh, purple when exhausted
• Kodak Indicator Stop Bath: Similar colour change
• Generic stop bath: Citric or acetic acid, may lack indicator

Using Stop Bath

Dilution: Follow manufacturer's instructions (typically 1+19 or similar)

Time: 30 seconds with continuous agitation

Capacity: Until indicator changes colour, or approximately 20-30 8×10 prints per litre

Between prints: Stop bath can remain in the tray for the session; it doesn't oxidise like developer.

Fixers for Paper

Fixer removes unexposed silver halides from the print, making the image stable and permanent.

Fixer Types

Rapid Fixer (Ammonium Thiosulfate)

The modern standard:

• Ilford Rapid Fixer: 1+4 dilution for paper
• Kodak Rapid Fixer: Similar characteristics
• Fixes RC paper in 30-60 seconds
• Fixes fiber paper in 2-4 minutes

Advantages:

• Fast fixing
• Clear results quickly
• Good capacity

Standard Fixer (Sodium Thiosulfate)

Traditional "hypo":

• Slower fixing (5-10 minutes)
• Very high capacity
• Some printers prefer it for archival work
• Less common now

Hardening vs Non-Hardening Fixers

Hardening fixer:

• Contains alum or similar hardener
• Makes emulsion more durable
• Can make washing less effective (hardened gelatin releases chemicals slowly)
• Not recommended for archival fiber work

Non-hardening fixer:

• No hardener added
• Standard for most modern work
• Easier to wash for archival permanence
• RC paper doesn't need hardening

Fixing Time

Underfixing:

• Leaves silver halides in the paper
• Print will eventually stain yellow/brown
• Appears hazy or milky when wet

Overfixing:

• Fixer attacks the image silver
• Highlights bleach out
• Shadow detail lost
• More common with strong or exhausted fixer

Correct fixing:

• RC paper: 30-60 seconds (1-2 minutes maximum)
• Fiber paper: 2-4 minutes in fresh fixer

Two-Bath Fixing

For archival fiber prints, two-bath fixing ensures complete and efficient fixing:

Method:

1. Fix in Bath 1 for half the total time
2. Fix in Bath 2 for half the total time
3. When Bath 1 approaches exhaustion, discard it
4. Move Bath 2 to Bath 1 position
5. Mix fresh fixer for new Bath 2

Why it works: The first bath does most of the work; the second bath finishes with fresher chemistry. Prints are never in exhausted fixer.

Testing Fixer Exhaustion

Hypo check solution: Available commercially or mix your own (potassium iodide solution).

Test method:

1. Add a few drops of hypo check to a small sample of fixer
2. If it turns milky or cloudy, fixer is approaching exhaustion
3. If it stays clear, fixer is still good

Approximate capacities:

• Rapid fixer 1+4: 24 8×10 prints per litre
• Two-bath system extends this significantly

Washing

Washing removes fixer and dissolved silver compounds from the print. Inadequate washing leads to staining and image deterioration over time.

RC Paper Washing

RC (resin-coated) paper has a plastic layer that prevents chemicals from soaking into the paper base.

Wash time: 5 minutes in running water

Method: Prints can be washed together in a print washer or under running water in a tray.

RC paper washes quickly and completely. Extended washing provides no benefit and may damage the resin coating.

Fiber Paper Washing

Fiber paper absorbs chemicals into the paper base, requiring much longer washing.

Without washing aid: 30-60 minutes in running water with complete water changes

With washing aid: 5-10 minutes after washing aid treatment

Archival standard: Washing until residual fixer tests show acceptable levels

Washing Aids (Hypo Clearing Agents)

Washing aids reduce wash time by helping release fixer from fiber paper.

Common washing aids:

• Ilford Washaid: Mix 1+4, treat prints for 10 minutes
• Kodak Hypo Clearing Agent: Similar protocol
• Perma Wash: Another option

Washing aid procedure:

This achieves archival washing in a fraction of the time of water-only washing.

Testing for Residual Fixer

For critical archival work, test prints for remaining fixer.

Kodak HT-2 Test (or equivalent):

1. Cut a small test strip from the print margin
2. Apply test solution
3. Compare colour to reference chart
4. Darker colour indicates residual fixer

If fixer remains, wash longer or repeat washing aid treatment.

Water Quality

Hard water: Can leave mineral deposits on prints. Use final rinse with distilled water or a wetting agent.

Temperature: Wash water should be close to processing temperature (18-24°C). Large temperature changes can cause reticulation.

Print Drying

Drying RC Prints

RC prints dry quickly and flat:

Air dry: Hang or lay flat on racks. Dries in 30-60 minutes.

Squeegee: Gently squeegee excess water from both surfaces, then air dry. Faster and reduces water spots.

Never: Use heat dryers designed for fiber paper—heat can damage the resin coating.

Drying Fiber Prints

Fiber prints are more challenging:

Screen drying:

• Place prints face-down on fibreglass or plastic screens
• Air dry for 4-12 hours depending on humidity
• Prints will curl significantly

Blotter drying:

• Place prints between clean photographic blotters
• Change blotters as they absorb moisture
• More even drying, less curl

Heated dryers:

• Drum or flatbed heated dryers
• Faster (minutes instead of hours)
• Can produce glossy finish on glossy paper (ferrotyping)
• Not recommended for archival work—heat can affect longevity

Flattening Fiber Prints

Dried fiber prints curl. Flattening options:

Dry mount press:

• Heat and pressure flatten prints
• 90°C for 30-60 seconds
• Use release paper to protect print surface

Weighted flattening:

• Stack prints between clean boards
• Weight heavily (books, etc.)
• Leave for 24-48 hours

Humidity and re-drying:

• Slightly humidify curled prints
• Re-dry under weights
• Time-consuming but gentle

Chemical Safety

General Precautions

• Ventilation: Work in a well-ventilated space. Fixer releases trace amounts of sulfur dioxide.
• Skin contact: Avoid prolonged contact with all chemicals. Use tongs, not fingers.
• Eye protection: Wear safety glasses when mixing concentrates.
• Don't eat or drink: Keep food away from chemistry.

Specific Hazards

Developers:

• Alkaline—can irritate skin with prolonged contact
• Some people develop sensitivity over time
• Metol (in some developers) causes allergic reactions in some individuals

Stop bath:

• Acidic—avoid splashes
• Mixing with developer releases heat

Fixer:

• Contains thiosulfate—relatively low toxicity
• Dissolved silver accumulates—creates hazardous waste if not handled properly

Disposal

Developer: Can generally be poured down the drain with plenty of water (check local regulations).

Stop bath: Neutralise with baking soda, then drain.

Fixer: Contains dissolved silver—a hazardous material. Options:

• Collect and take to hazardous waste facility
• Use silver recovery system (electrolytic or chemical)
• Some labs accept used fixer for silver recovery

Equipment for Processing

Summary

• Develop for full time (60-90 seconds)—never pull early
• Stop bath extends fixer life; indicator shows when exhausted
• Fix correctly: 30-60s for RC, 2-4 minutes for fiber; don't overfix
• Two-bath fixing ensures complete fixing for archival fiber prints
• Washing aids dramatically reduce fiber paper wash times
• Test residual fixer for critical archival work
• RC dries fast and flat; fiber requires time and flattening
• Maintain proper chemistry—fresh developer for final prints
• Dispose of fixer properly due to silver content

Print processing chemistry is straightforward once you understand the purpose of each step. Consistency—same times, same temperatures, fresh chemistry—produces predictable results. Master the basics before experimenting with variations.