The clearing bath is a critical step in the platinum and palladium printing processes, as it removes residual ferric salts that can cause staining and degrade the image over time.
Besides properly washing the platinum and palladium print, your clearing bath chemistry choice and workflow are the biggest determinants of your prints’ longevity and archival performance.
It isn’t a sexy topic, but it can make a difference in your platinum and palladium prints.
In this article, I’d like to give you information about your chemistry choices and the workflow I use to make my platinum and palladium fine art archival prints.
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Here is a detailed review of common clearing bath options, including their chemistry and pH levels and why these factors matter.
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Hydrochloric Acid (HCl) Clearing Bath
Chemistry:
- Solution: Typically a 3-5% solution of hydrochloric acid in water.
- Reaction: HCl reacts with ferric oxalate and other iron salts, converting them into soluble iron chlorides which can be easily washed away.
pH Levels:
- pH: The pH of a 3-5% HCl solution is approximately 1-2, making it highly acidic.
Why pH Matters:
- The strong acidity of HCl ensures rapid and effective removal of iron salts.
- However, the highly acidic environment can potentially damage the paper or affect the image stability if not used carefully.
Usage:
- Immerse the print in the HCl solution for about 5-10 minutes.
- Follow with thorough washing to remove all traces of acid.
- HCl is not a valid option for most people, and it is not a path that I recommend.
Citric Acid Clearing Bath
Chemistry:
- Solution: A 3% citric acid solution in water (30g per liter).
- Reaction: Citric acid chelates iron ions, forming soluble complexes that can be washed out.
pH Levels:
- pH: The pH level of this citric acid solution is approximately 2-3, moderately acidic.
Why pH Matters:
- Citric acid is less aggressive than HCl, reducing the risk of damage to the paper.
- The moderate acidity is still effective in clearing iron salts while being gentler on the print.
Usage:
- Soak the print in the citric acid solution for 5-10 minutes.
- Follow with thorough washing to ensure complete removal of the clearing agent.
EDTA Clearing Bath
Chemistry:
- Solution: Typically a 1-2% solution of disodium EDTA in water.
- Reaction: EDTA is a powerful chelating agent that binds to iron ions, forming stable, soluble complexes.
pH Levels:
- pH: The pH of a disodium EDTA solution is typically around 4-5, slightly acidic to neutral.
Why pH Matters:
- The near-neutral pH of EDTA is very gentle on both the paper and the image, minimizing the risk of damage.
- The chelating action is highly effective at removing iron salts without affecting the print’s integrity.
Usage:
- Immerse the print in the EDTA solution for 10 minutes for two or more baths.
- Follow with extensive washing to remove all EDTA and any residual iron complexes.
Sodium Sulfite Clearing Bath
Chemistry:
- Solution: A 1% solution of sodium sulfite in water.
- Reaction: Sodium sulfite acts as a reducing agent, converting ferric ions to ferrous ions, which are more soluble and can be washed away.
pH Levels:
- pH: The pH of a sodium sulfite solution is around 8-9, mildly alkaline.
Why pH Matters:
- The mildly alkaline environment helps neutralize any residual acidity in the print, which can be beneficial after an acidic sensitizing and development process.
- The reducing action of sodium sulfite is effective at clearing iron salts while being gentle on the print.
Usage:
- Soak the print in the sodium sulfite solution for 5 minutes before your final wash.
- Follow with thorough washing to remove all sodium sulfite and residual iron.
Summary
Each clearing bath option offers distinct advantages and considerations:
- Hydrochloric Acid: Highly effective but very acidic; requires careful handling and thorough washing. I don’t recommend using it.
- Citric Acid: Moderately acidic; effective yet gentler on the print.
- EDTA: Near-neutral pH; very gentle and effective, ideal for preserving print integrity.
- Sodium Sulfite: Mildly alkaline; effective at clearing and neutralizing residual acidity.
Choosing the right clearing bath depends on the specific needs of the print and the desired balance between effectiveness and gentleness. Proper use of these clearing solutions ensures the longevity and quality of platinum and palladium prints by effectively removing residual ferric salts and stabilizing the image.
Consensus on the Most Effective Clearing Bath
In the platinum and palladium printing community, there is a general consensus that a combination of clearing baths yields the most effective results. I agree and I share my thoughts and process with you below.
This multi-step approach ensures thorough removal of residual ferric salts and optimal print stability. Among the various options, citric acid followed by an EDTA bath is widely recommended for its effectiveness and balance between thorough clearing and gentleness on the print.
Why a Multi-Step Approach is Recommended
• Balanced Effectiveness and Gentleness: Citric acid effectively breaks down and removes a significant portion of ferric salts without being too harsh on the print. EDTA then follows up by chelating and removing any remaining ferric ions with minimal risk of damage due to its gentle, near-neutral pH.
• Comprehensive Clearing: The two-step process ensures a more thorough removal of ferric salts than using a single clearing agent. Citric acid initiates the clearing by addressing the bulk of the ferric salts, and EDTA completes the process by binding and removing any residual ferric ions.
• Optimal Print Stability: By effectively removing all ferric salts and washing thoroughly, the risk of staining and degradation over time is minimized. Using both acids ensures that the print remains stable and retains its quality for generations.
• Ease of Use and Availability: Both citric acid and EDTA are relatively easy to obtain and handle, making this approach accessible for many photographers.
Converting Tetrasodium EDTA to Disodium EDTA Using Oxalic Acid
If you have tetrasodium EDTA and need disodium EDTA for your clearing bath, you can convert it by adjusting the pH of the solution using oxalic acid. I only like to purchase tetrasodium EDTA because it makes things easier, and I convert it to disodium EDTA for a better clearing bath for my platinum and palladium prints.
Here’s how you can do it:
Prepare a Tetrasodium EDTA Solution: Dissolve the required amount of Tetrasodium EDTA in distilled water. For example, dissolve 20 grams of tetrasodium EDTA in 1 liter of water.
Adjust the pH with Oxalic Acid: Gradually add oxalic acid to the solution while constantly stirring and monitoring the pH. The target pH for converting tetrasodium EDTA to disodium EDTA is around 4-5. Add small amounts of oxalic acid until the desired pH is reached. I use simple pH test strips for the tests. When I mix 1500ml of the EDTA solution, I have found that if I add 10g of oxalic acid, the pH will come down to the 4 to 5 range as desired. That is about 6g per liter of 3% EDTA solution.
Check pH Levels: Ensure the solution reaches the desired pH level of 4-5. Adding oxalic acid converts some sodium ions to hydrogen ions, effectively converting tetrasodium EDTA to disodium EDTA. Once you go through this process a time or two, you will likely decide to use a pre-determined amount of oxalic acid to adjust the pH level.
Prepare the Final Disodium EDTA Solution: Once the pH is adjusted to 4-5, your solution primarily contains disodium EDTA and is ready for a clearing bath.
Recommended Workflow for Archival Clearing
Here is the exact workflow suggested to ensure proper clearing of platinum and palladium prints:
Step 1: Initial Rinse
Rinse in Distilled Water: Immediately after developing, rinse the print in a tray of distilled water for about 2 minutes to remove any surface developer. Discard the distilled water and do not reuse it again.
Step 2: Citric Acid Bath
Prepare Citric Acid Solution: Mix a 3% citric acid solution (30 grams of citric acid in 1 liter of distilled water).
- pH: Approximately 2-3.
First Clearing Bath: Immerse the print in the citric acid solution for 5 minutes. Gently agitate the tray to ensure even exposure to the acid throughout the 5 minute time period.
Rinse in Distilled Water: Transfer the print to a tray of distilled water and rinse for 2 minutes, changing the water at least once during this period to ensure thorough removal of residual acid.
Step 3: EDTA Bath
Prepare EDTA Solution: Mix a 2% solution of disodium EDTA (20 grams of disodium EDTA in 1 liter of distilled water). If starting with tetrasodium EDTA, adjust the pH as described above.
- pH: Approximately 4-5.
Second Clearing Bath: Immerse the print in the EDTA solution for 5 minutes. Gently agitate the tray to ensure thorough clearing.
Rinse in Water: Transfer the print to a tray of distilled water and rinse for 5 minutes, changing the water at least once during this period to ensure complete removal of the clearing solution.
Step 4: Sodium Sulfite Bath
Sodium Sulfite Bath: To further remove residual iron and neutralize acidity, use a 1% sodium sulfite bath (10 grams of sodium sulfite in 1 liter of distilled water) for 5 minutes.
pH: Approximately 8-9.
Step 4: Final Wash and Rinse
Final Wash: Place the print in an archival print washer for at least 30 minutes, using running water to remove any remaining chemicals. This step is crucial for ensuring the print’s archival quality. If your paper can tolerate a 60-minute wash, I suggest using the longer washing time. You have invested this much time, effort, and money to make a beautiful and archival platinum and palladium print. I see no reason to cut corners and try to save 30 minutes at this point.
If you don’t own an archival print washer, you can place the print face down in a tray and lay some wet cotton balls on the back to help keep the print’s surface just below the water level. The key is to keep water moving across the print. You can also modify an old darkroom tray by drilling some small holes on one end to help the water flow better.
Final Rinse in Distilled Water: After the sodium sulfite bath, rinse thoroughly in distilled water for 2 minutes. I change out the distilled water at the 1-minute mark as a final attempt at doing everything I can to ensure the archival stability of my handmade platinum and palladium fine art prints.
Conclusion
The combination of citric acid followed by EDTA is considered the most effective and widely recommended clearing workflow for platinum and palladium prints. This approach thoroughly removes ferric salts, maintaining the print’s archival quality while being gentle on the paper and the image. Proper clearing and rinsing are essential for the longevity and stability of these fine art prints.
If you enjoyed this article, share your thoughts and comments below.
If you enjoy slowing down with film, darkroom printing, and meaningful photography, consider subscribing to my YouTube Channel. I share new videos each week focused on simple tools, timeless techniques, and the quiet joy of analog.
I am making platinum and palladium prints for my Pictorial Whispers project, and I wanted to share this information with you today to help you in your work.
Darkroom Diary Premium Members receive exclusive access to my technical notes, presentations, videos, and chemistry notes used to create handmade calotype paper negatives, wet plate collodion negatives, and salt prints.
Consider becoming a premium member to support my monthly creative and technical articles and videos dedicated to analog photography. Your membership directly helps me continue publishing unique, high-quality content exclusively for analog photography enthusiasts like you.
