Washing

From Silvergrain Research

Films, plates and prints must be thoroughly washed after processing before drying. This is because residues of some processing chemicals and reaction products are detrimental to the image if not washed out. The harmful chemical residues that need to be washed out are:

• thiosulfate, the active ingredient of all practical fixers
• silver-thiosulfate complex ion made in the fixing reaction
• developing agents and other processing chemicals

(a non-issue in most conventional processing)

• toning agents (sulfide, selenide, polysulfide, etc.).

The amount of washing necessary is determined by (1) material and the fixer used. For most efficient processing and washing experience, it is highly recommended to use a non-hardening rapid fixer. Consult fixer for further information.

Contents 1 Summary Recommendations 2 General guidelines 2.1 Avoid hardening fixers 2.2 Film 2.3 RC prints 2.4 Fiber (baryta) prints 3 Archival standards 4 Mechanism of washing 5 Controversy of overwashing 6 Controversy of Ilford rapid washing sequences 7 Additional Caution

Summary Recommendations

Although the washing requirement depends on the particular material and washing conditions, this table can be used to find a range of washing time typically recommended for archival processing, with slow, continuous flow of washing water at 13 to 25C or 55 to 77F. More detailed discussion will be found in the later part of this article.

Washing time guideline
Fixer	Film	RC paper	FB paper
Acid hardening fixer	15-20 min	15-20 min	* (30+ min)
Non-hardening rapid fixer	5-10 min	1-4 min	* (10-20 min)
Alkaline rapid fixer	1-3 min	1-3 min	* (10-20 min)

* Use of washing aid is highly recommended. Times in the parentheses are time necessary without washing aid.

Washing time requirement varies significantly depending on the flow rate and agitation of the wash water. It also varies depending on the fixer formula. Follow the individual product's instruction for the more exact washing procedure.

General guidelines

• Materials fixed in a hardening fixer always require much longer washing time to wash out the residual chemicals to the same level. Avoid hardening fixers unless it is absolutely necessary (very rare in manual processing of modern films and papers; see the hardening fixer section below.).

• Non-hardening rapid fixer is a very time-efficient choice, as it fixes the material much faster and it also washes out much faster.

• A non-hardening rapid fixer with its pH adjusted to 6.5 to 8.5 are very fast in washing, and it is most time-saving as well as water-saving choice. This type of fixer is commonly called Neutral Rapid Fixer or Alkaline Rapid Fixer. These are highly recommended.

• Always fix materials for at least twice the clearing time. Materials that are barely fixed to clearing time will require much longer washing time due to incomplete chemical conversions of fixing reaction products. They are invisible (thus the film is already cleared) but extra fixing time will ensure that the material is completely fixed and thoroughly washed.

• Do not let the fixer to exhaust. Fixers that are exhausted may still continue to fix the material without problem but they hinder washing process. Replace the fixer when the processing capacity limit is reached.

• Use two-stage fixation or washing aid when possible. These techniques maximize the processing capacity of the chemicals and also ensures high quality processing results with good reliability.

• Do not use distilled, deionized or otherwise pure water for washing. They are significantly less efficient in removing thiosulfate from films and prints, compared to plain tap water.

Avoid hardening fixers

Acid hardening fixer used to be the standard fixer for most darkroom work to prevent damage to the emulsion (such as scratches or frilling) during washing.

However, all modern films and papers made for pictorial photography are very much hardened during manufacturing due to the advancement in gelatin hardener technology. Modern materials are already highly resistant to scratches and other damages during manual processing. Use of hardening fixer bath will require much longer washing time with more washing water, although the hardener does not provide any useful benefit. Therefore, hardener is no longer necessary and many experts recommend non-hardening fixers today.

One very common misconception is that hardening fixer prevents emulsion scratch or damage while you are organizing or printing the negative. This is unfortunately a very persistent misconception, and it is even written in some darkroom manual books and even product advertisements.

The emulsion hardener is effective only while the emulsion is completely wet. Once dried, both hardened and non-hardened emulsions have very similar mechanical strengths including scratch resistance. Use of hardener does not make the emulsion more resistant to humidity or fungus growth, and it does not ease the requirement for proper storage conditions.

Film

For roll and 35mm films processed in spiral reels, a highly efficient and fast fill and dump washing system is advocated by Ilford. This method is eco-friendly because of much smaller amount of water it requires compared to continuous flow washing, while ensuring very low residual thiosulfate level to meet the ISO archival standard. Specifically, in the test performed by this author, the residual thiosulfate level is well below 10 milligrams per square meter, while the ISO standard (life expectancy greater than 500 years for polyester film base) requires the residue be less than 14 mg per square meter.

Ilford "fill and dump" washing sequence

1. Process the film in spiral reels.
2. Fix it using a non-hardening rapid fixer, such as Ilford Universal Rapid fixer or Silvergrain Clearfix.
3. After fixing, fill the tank with water and invert it 5 times.
4. Drain the water and refill. Invert the tank 10 times.
5. Drain and refill it for the third time and invert the tank 20 times. Drain.

Sheet films and plates are washed in slowly running water. Washing time is typically 5-10 minutes with non-hardening fixers and 15-30 minutes with hardening fixer. The flow should be adjusted so that the wash water bath is evenly circulated, and replaces the water at least 3 times during the washing period. Too fast a flow rate may cause damage to the film, it is best to choose slow flow rate with many tiny inlets in the washing tank/tray, and give adequate washing time.

There are film washers that wash roll and 35mm films in spiral reels by continuous flow of water. Some processing tanks (e.g., Paterson tank system) can be converted to a washer of this type by attaching a hose. The washing time and flow rate should be determined similarly to the sheet film procedure above. This is because the level of agitation given by the water flow is much more gentle than the manual inversion of the tank, requiring much longer washing time than the Ilford fill and dump method above.

RC prints

Relatively short washing is sufficient for resin coated papers. This is because their substrates are laminated with impermeable polyethylene layers, preventing the processing chemicals to soak into the paper fiber. The sizing layer of RC paper is also in the polyethylene layer and they do not adsorb the processing chemicals. Therefore, the task of washing RC prints is to remove the fixer from the surface of image-forming silver grains and gelatin in the emulsion layer. If non-hardening rapid fixer is used, washing in running water for 2 minutes is adequare for these materials. Washing time can be further shortened by use of (1) vigorous agitation, (2) washing water of at least 13C or 55F, (3) use of alkaline rapid fixer.

Again, use of hardening fixer would prolong the minimum washing requirement, and is not recommended. All modern RC papers are sufficiently hardened during manufacturing and they do not require or benefit from using hardener in processing.

Fiber (baryta) prints

Washing of fiber based paper requires more elaborate washing.

The substrate paper fiber and baryta sizing layers adsorb the fixer and its reaction products, and they are harder to remove (see the mechanism section below). Much of them can be removed by a few minutes of washing, but at this point, some fixer and fixing reaction products are stubbornly adsorbed to the fiber and sizing material in the emulsion base, and they must be desorbed and washed out, to meet a reasonable archival standard.

The most effective way is to use a washing aid. The fiber paper print is rinsed in water for 2-3 minutes, and then immersed in washing aid for 3-5 minutes with intermittent agitation. The treated printed can be washed in 10-20 minutes to meet the archival standard. However, the washing efficiency varies depending on the washing water agitation, water temperature, and water impurity.

Ilford advocates a rapid "optimum permanence" sequence (it's also called by "archival sequence"), which is a particular procedure that falls under the description of the previous paragraph. The Ilford sequence is highly effective and requires much less water.

Ilford "optimum permanence" sequence

1. Fix in a non-hardening rapid fixer, such as Ilford Rapid fixer (1+4) or Silvergrain Clearfix (1+4), for 1 minute.
2. Wash the print in running water for 5 minutes.
3. Immerse the print in a washing aid, such as Ilford Washaid (1+4) or Silvergrain Clearwash (1+19) for 10 minutes. Give intermittent agitation.
4. Wash the print in running water for 5 minutes.

For more information, consult the fixer manufacturer's instruction.

The above procedures are for non-hardening rapid fixers. If hardening fixer is used, the last wash cycle needs to be extended to 20-40 minutes. Hardening fixer is rarely necessary in manual processing of modern papers, and it is not recommended.

Archival standards

There are ISO standards for maximum level of residual thiosulfate for various kinds of materials and life expectancy. Different criterion is set for each emulsion type and each substrate (base material) type. Limits for most continuous tone negative films and printing papers fall in the range of 14 to 50 milligrams of thiosulfate per square meter of the washed material. The actual values are included in the section residual thiosulfate tests.

This level of residual thiosulfate is easy to achieve by simply following the direction for appropriate category above.

Mechanism of washing

The process of washing out thiosulfate from film and prints is chemically speaking a two-stage process. Much of the thiosulfate may be freely contained in the swollen gelatin layer, but a good amount of thiosulfate are tightly bound (adsorbed) on the surface of image silver, baryta sizing material (used in FB paper), cellulose fibers (FB paper) as well as gelatin molecules in the emulsion coating. In the case of hardening fixer, the hardener in the fixer makes a chemical change to the gelatin molecule (crosslinking) and the crosslinking sites are particularly strongly adsorbed by thiosulfate. These stubbornly adsorbed thiosulfate must first come off the host molecule that they are bound to. This is the first step, called desorption.

The second step is to remove the free thiosulfate from the gelatin layer, the sizing layer, and the cellulose fiber material to the washing water. This is the second step, called diffusion process.

Of the two processes, the first step, desorption is much slower process. Washing aid accelerates this first step by means of ion displacement. The desorption process requires more energy to activate, that is, it is more temperature sensitive. Use of washing aid also makes the washing process less temperature sensitive, that is, the material can be thoroughly washed in very cold tap water without requiring extended washing time. The diffusion process is also temperature sensitive, but less so than the desorption process.

Controversy of overwashing

Thiosulfate, the main active ingredient of all practical fixers, can cause image to discolor or fade, if it is inadequately washed out. Therefore, the more complete the washing process, the better for the image. However, a new paradox was born when Fujifilm and Kodak scientists found a curious phenomenon that a trace amount of residual thiosulfate can actually protect the image compared to very thoroughly washed image. Since then, the mechanism of image deterioration has been elucidated much farther, and the reason for this paradox is also understood to practically sufficient level. This is the origin of the notion of overwashing.

The caution against overwashing has two implications:

1. Do not waste your effort uselessly by washing longer than necessary.

2. Do not overwash because it may decrease the image stability.

The point 1 is fairly obvious. Removing thiosulfate does not improve image stability after a certain point. In reality, if you wash to meet the archival standard, there is no point to waste more time and water to decrease the image stability.

The point 2 is more tricky. It is impractical to control the level of residual thiosulfate to the optimal range by adjusting the washing time. Furthermore, the amount of image protection from even the optimal level is insufficient to protect images for display or average (i.e., non-museum level) storage condition. For example, much stronger level of protection can be provided by Ag Guard or any of the archival toning process.

If you are processing for the highest possible image stability, as most fine art photographers should be, then the issue is completely thrown out of consideration, since the protection provided by such a low level of thiosulfate is insufficient. In such case, the print should be toned in any of the archival toning processes, and washed very thoroughly.

The "overwashing" paradox is a greater source of headache for darkroom chemical manufacturers, especially the person who makes the usage instruction. This is because they know that "overwashing" exists and it is counterintuitive to average darkroom workers. Manufacturers need to emphasize to the users that (1) adequate level of washing is very important to the longevity of the image, and (2) they shouldn't wash much more than recommended. This is a very tricky issue in phrasing instructions, and each manufacturer thinks hard to be as "informative" and "courteous" but without making the instruction overly complicated or confusing. One example is that many manufacturers overly emphasize it is unnecessary to use more washing time than indicated. They may also emphasize that there is no need to use washing aid for RC prints as long as the fixer is fresh. They would still recommend polysulfide, selenium or gold toner if you are serious about image permanence.

Thus "overwashing" should be regarded as a caution against waste of useless effort rather than an active means to increase image permanence. Most serious photographers want to protect their images by polysulfide, gold or selenium toning, and completely overthrow this paradoxical notion of "overwashing."

Controversy of Ilford rapid washing sequences

Some authors voiced concerns for short washing time required by the Ilford washing sequence, particularly for films. They come with various flavors of story, sometimes citing casual conversation from Kodak engineers. However, independent tests indicate that Ilford procedure is completely adequate to meet (and indeed exceed) the ISO standard for life expectancy longer than 500 years, with a significant safety margin, as long as the instruction is followed closely.

Important factors are the same as what are already listed in general guidelines.

• Use non-hardening rapid fixer, which is typical of Ilford fixers
• Fix the material for at least twice the clearing time with good agitation
• Never use exhausted fixer
• Follow the washing instruction carefully

Some users still feel insecure due to much shorter washing time than what they were taught before. The huge difference in washing time requirement indeed comes from the difference in the washing properties of standard Kodak fixers decades ago (they recommended hardening fixers) and the more modern standard of non-hardening rapid fixers. One cannot use Ilford rapid sequence with acid hardening fixer, rapid or otherwise. With such a fixer, the slow washing method such as one recommended by Kodak must be used.

After all, if a user still feels insecure, I suggest the following:

• Ilford rapid washing process, when correctly executed, provides good washing to the ISO archival standard
• There is no harm in adding an extra cycle or even repeating the whole washing sequence twice, although such additions are unnecessary.
• Use residual thiosulfate tests to confirm the adequacy of washing process with your own material, your fixer of choice, and your washing water.

This author routinely runs residual thiosulfate tests in darkroom each time new processing chemicals or new material is introduced. His current standard washing technique is very similar to or identical to the Ilford sequences, and there has been not a single incidence where the residual level was too high to meet the ISO standard. Specifically, the residue level is well below 10 milligrams per square meter, while the ISO standard requires the residue be less than 14 mg per square meter. In fact, in literature, there is not a single report of the failure with credible evidence.

The "controversy" of the Ilford washing techniques is based on the fear from drastically shorter washing instruction from what most users are used to. Those who understand the chemistry behind it, and also test their own material have no concern about the Ilford method. There is no controversy, after all.

Additional Caution

Although proper processing, complete fixation, thorough washing are all essential to make archival prints, increasing number of incidences of image deterioration is due to oxidative attacks from environmental pollutants, such as automobile exhausts and fumes from various materials, such as room paints, storage box, and adhesives. What this means is that archival washing itself does not ensure that the image will last for many decades in average storage conditions.

A very important consideration should be given to storage conditions discussed in conservation and archival process. Also, important prints should be toned by any of the archival toning process, most preferably by polysulfide toning (brown toner made from liver of sulfur) to increase the durability of the image itself.