Alternative to Orwo C 9165-UT-18 in C-41, RA-4 or ECN-2

This article is about the development of Orwo reverse films, here the UT-18, in currently available photoochemistry as an alternative to the Orwo C-9165 which is based on CD-1.

Chemical basis of dye formation in ORWO processes (e.g. C-9165)

The main difference between the historical ORWO color process and modern processes such as C-41 or E-6 lies in the mechanism of dye formation. It is a two-step process.

1. Formation of dye precursors

In the first step, the color developer (CD-1) reacts with the color couplers stored in the emulsion. However, the result of this reaction is not the final, stable dye, but a colorless or very pale precursor, a so-called leuco dye.

2. Oxidation of the dyes by the bleach

The final, visible dye is only created in a second, subsequent oxidation step. In the ORWO process C-9165, this task was carried out by a strongly oxidizing bleaching bath based on potassium ferricyanide. The bleach therefore had a dual function:
Removal of the metallic silver, oxidation of the leuco dyes to the final, strong color dyes.

Incompatibility of modern processes
Modern bleaching baths (e.g. in C-41, E-6, ECN-2) are usually based on milder complexing agents such as EDTA. Their oxidative power is not sufficient to convert the leuco dyes of the old ORWO films into their final form. They simply remove the silver, leaving the dyes in their pale precursor state. This is the chemical cause of the weak colors in cross-processing experiments.

Mechanical stabilization of the emulsion
Additionally, the gelatin emulsions of ORWO films were mechanically less stable than modern materials. The original C-9165 process therefore necessarily contained a hardener, often as part of the fixing bath (hardener-fixer), to physically stabilize the emulsion during wet chemical processing and to avoid damage.

The current status is as follows:

1. SW development HC-1110 Dilution B 1:31 at 25 ° C with 1% bzt addition 20ml/l
2. Water as a stop 5 min.
3. Second exposure 2+2 minutes with 50W LED
4. Water 2 min.
5. Color development (ECN-2) 20 minutes at 25 ° C, tested with Cinestill CN-2 and addition of 1.2g/l CD-3
6. Water thoroughly15 minutes!
7. Bleaching bath 15 minutes, tested with 5G/l potassium ferricyanide (potassium hexacyanidoferrat (III) + 10g/l potassium bromide
8. Water 5 min
9. Fix 15 minutes, tested with Adox adofix P II 40g/l
10. Water 5 min
11. dry

Here are the results for a UT-18 135, good results appear around ISO1.5-3, more light shifts the white balance towards blue.

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What I have learned so far – basic principle of subtractive color mixing. The finished dyes of a positive are cyan, magenta, yellow. The weaker one of these dyes is, the more the mixed color of the remaining two dominates:

• little magenta → cyan + yellow dominate → GREEN.
• little yellow → cyan + magenta dominate → BLUE/CHARCOAL BLUE.
• little cyan → magenta + yellow dominate → REDISH / MAGENTA.

(Note: “Blue shift” can also arise from the spectral position of the dye curves, not just the difference in quantity.)

What CD-3 typically does with (aged) UT-18 — technically explained

CD-3 is sterically substituted differently than CD-4/CD-1.

This influences:

• Diffusion in dense/aged gelatin (CD-3 can penetrate more slowly)
• Reaction rate with certain couplers (selective coupling)

In alten UT-18-Chargen kommt es häufig vor, dass die Magenta-Schicht empfindlichkeits- oder kopplungs-geschwächt ist (Alterung, Sensibilisierungsdifferenzen).

If the developer (CD-3) reacts less well with the magenta coupler, less magenta dye is produced.

Consequence: If CD-3 is used (or if the coupling is poor with the existing coupler), the positive often looks greenish - because magenta is missing and cyan+yellow predominates. In other cases (depending on the exact coupler spectrum), CD-3 can also produce a yellow shift (more yellow, less magenta) or overall “dirtier” tones.

Kurz:

• CD-3 → common: magenta underformation → GREEN tinge (in UT-18 scenarios)

How we might get better results here:

• Switch to CD-4 (golden rule): if CD-4 gives more neutral results, stick with it
• Increasing color development time: +10-30% (at 20-25°C) can provide more coupling — but be careful: check for fog/overdevelopment.
• Slight increase in CD-3 concentration (if you want to keep CD-3): e.g. B. from 4.0 → 5.2 g/L (I have already tested it with the Cinestill CN2). More color formation, but also more haze.
• pH fine-tuning: CD-3 is sensitive to pH; slightly higher pH (0.1-0.2 pH points) can improve coupling — again: risk check for haze.
• Iodide addition (small amount): protects unexposed crystals, can improve contrast and clarity in shadows; This often helps to reduce “dirty” yellow tones.
• Benzyl alcohol addition: Higher effective sensitivity: The developer would work more aggressively. Better color saturation and density: The benzyl alcohol helps the CD-3 penetrate deeper and more completely into the (hardened) emulsion layers and the color couplers. This would result in stronger, richer colors and a deeper black (Dmax). The pale, washed-out tones would probably gain significant strength. Increased contrast: Accelerated development usually results in steeper contrast. This can be good to give the old, often dull film more “bite”. Risk: Since the Cinestill kit is already balanced for a specific result (without benzyl alcohol), adding the accelerator could increase the contrast too much, causing the lights to burn out.
• Bromide/retarder reduction in initial development: more silver available for color development may promote magenta — must be carefully tested. Here it is probably easier/more reproducible to adjust the development time.
• Raising the temperature slightly (e.g. +2-3 °C) increases reaction kinetics and diffusion - but here at 25 °C you are already at the limit of the original C-9165 process

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To understand why CD-4 is probably the better developer, you can look at the molecular structure.

Explanation

CD-1 is a relatively small p-phenylenediamine derivative (often with diethyl groups).

The ‘fit’ refers to how well the developer molecule can dock to the color couplers in the film to trigger dye formation. This is strongly influenced by the size and shape of the side groups (the substituents on the nitrogen).

• CD-1: The reference with small, flexible ethyl side groups.
• CD-3: Has a very large and bulky side group (e.g. with glycolamide or sulfonamidoethyl moieties). This size results in ‘steric hindrance’, i.e. the molecule is too large and does not fit efficiently with the couplers optimized for the smaller CD-1 (or CD-2).
• CD-4: Has side groups (e.g. ethyl and hydroxyethyl) that are significantly closer to CD-1 in size and flexibility than those of CD-3. Therefore, CD-4 can dock better with the color couplers of the CD-1-based film due to its more compact structure. It's still not a perfect fit, but significantly better than CD-3.

Possible recipes for further experiments based on CD-3 and CD-4:

Recipe: CD-3 color developer (E-6 similar)

In this variant, ascorbic acid is used as an antioxidant instead of hydroxylamine sulfate.

Chemicals (for 1 liter of working solution)

Water (distilled, approx. 50°C)	800 ml
Potassium carbonate (anhydrous)	25.0 g
Sodium sulfite (anhydrous)	5.0 g
Calium cherromas	0.2 g
Ascorbic acid (vitamin C)	2.5 g
Benzylalkohol	7.5 ml
Propylene glycol or glycerin, replaces diethylene glycol (optional)	12 ml
CD-3 (Color developer agent 3)	5.0 g
Potassium iodide (very optional)	10 mg
With distilled Fill up with water	1000 ml

Instructions for mixing

1. Start with 800ml of warm, distilled water.
2. Dissolve the chemicals exactly in the order given above. Always wait until one chemical is completely dissolved before adding the next.
3. After all chemicals are dissolved, make up the solution with cold, distilled water to a final volume of exactly 1 liter.
4. Allow the solution to cool to working temperature (typically 25°C) before use.

Important instructions

• PH value: The target pH value for this developer is approx. 11.9 — 12.0. Adjustment with 1% acetic acid and/or 1% sodium hydroxide solution (caustic soda).
• Note on ascorbic acid: Ascorbic acid is, as the name suggests, an acid and lowers pH. The amount of potassium carbonate listed is a starting point. It is indispensable, check the pH of the finished solution with a calibrated measuring device and, if necessary, adjust it to the target value by carefully adding more potassium carbonate (preferably as a solution).
• Temperature: The standard working temperature for the E-6 process is 38°C ± 0.3°C, we use it here at 25°C.
• Durability: The solution prepared does not last very long. Store in a full, airtight bottle and consume within a few weeks.

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Recipe: CD-4 color developer (C-41-like)

This developer is the standard for color negative films. Here too, ascorbic acid is used as a safer alternative to hydroxylamine sulfate.

Chemicals (for 1 liter of working solution)

Water (distilled, approx. 40°C)	800 ml
Sodium sulfite (anhydrous)	4.25 g
Ascorbic acid (vitamin C)	2.5 g
Benzylalkohol	5.5 ml
Propylene glycol or glycerin, replaces diethylene glycol (optional)	12 ml
CD-4 (Color developer agent 4)	4.75 g
Potassium carbonate (anhydrous)	30.0 g
Calium cherromas	1.3 g
With distilled Fill up with water	1000 ml

Instructions for mixing

1. Start with 800ml of warm, distilled water.
2. Dissolve the chemicals here too exactly in the order given.
3. After all components have completely dissolved, make up the solution to 1 liter with cold, distilled water.
4. Allow the solution to cool to working temperature before use.

Important instructions

• PH value: The target pH for the C-41 developer is 10.0 ± 0.03. Adjustment with 1% acetic acid and/or 1% sodium hydroxide solution.
• Note on ascorbic acid: Since ascorbic acid is acidic, it is important to check the pH value at the end of mixing with a calibrated pH meter. The specified amount of potassium carbonate serves as a guideline. If necessary, the pH value must be adjusted to the exact target value by further adding a potassium carbonate solution dropwise.
• Temperature: The standard working temperature for the C-41 process is 37.8°C ± 0.15°C. Small deviations already have a major impact on color rendering. We use it at 25°C.
• Durability: Similar to the CD-3 developer, the solution should be stored in a cool, dark place with the exclusion of air and used quickly.

Recipe: bleach bath

This bleach bath is an adapted standard potassium ferricyanide bleach bath.

Chemicals (for 1 liter of working solution)

Water (distilled, approx. 25°C)	800 ml
Potassium ferricyanide	65 g
Calium cherromas	50 g
Natriumdihydrogenphosphat (Monohydrat)	20 g
Natriumhydroxid (NaOH) (als 10%ige Lösung)	5-10 ml – siehe Hinweise
With distilled Fill up with water	1000 ml