Bladderwrack seaweed developer for black and white film

Seaweed developer offers an alternative to using store-bought developer and is very similar to the Caffenol-C film development process. This developer is designed for black and white film, with 400 ISO. Melanie King developed this recipe as part of the Sustainable Darkroom online residency, with the London Alternative Photography Collective.

Writer and photography / Melanie King

Photograph developed with seasweed by Melanie King
Photograph developed with seaweed by Melanie King

Developing with a seaweed developer is more sustainable than shop-bought developer. As with all foraging, it is suggested that you adhere to the forager’s code, being careful with the environment when collecting seaweed. Make sure that you correctly identify the seaweed that you plan to use, and that you do not take more than you need. You should pick seaweed ideally from where it is growing or freshly washed up from the seashore, as fresh as possible. Be careful not to damage the plant as cutting incorrectly can prevent further growth. Cut the blades off above the stipe, leaving a little of the blade so that it can grow again.
If using washed-up seaweed, proceed with caution as seaweed can hold toxins that are found within the ocean. You know that it is safe if it is fresh from the plant or freshly washed up from the tide (go picking just after low tide).

I use the technique below, for a 35mm Ilford HP5 film. Double the recipe for a 120 film.

How to develop film with seaweed

  1. Collect a handful of fresh bladderwrack seaweed – about 150g.
  2. Boil 500ml of hot water, pour onto the seaweed and leave overnight.
  3. In a separate jug, mix 50g of soda crystals with 150ml water and dissolve completely.
  4. In the jug with dissolved soda crystals, mix 12g vitamin C with the dissolved soda crystal solution and dissolve completely.
  5. Add around 150ml of your seaweed “brew”.
  6. Heat to 26-30 degrees. You can do this by putting the jug of seaweed developer into a larger jug of hot water.
  7. Pour the developer into your developing tank. Invert the tank every 2 minutes for 60 minutes. You can also stand develop for the full hour but this may create bromide drag.
  8. Wash for 2 minutes.
  9. Fix as usual with Ilford Rapid Fix, and put a copper pipe in the fixer for 12 hours. The copper collects the silver from the fix, so that less silver material is deposited into the waterways.
  10. You can try using salt water instead of fixative to stabilise your film. Salt has a dissolving limit of 359g per litre. So for a 35mm film you could mix the following solution. 150g salt with 500ml water. You will then need to leave the film in the salt water for 24 hours.
  11. Wash for 10 minutes, and hang to dry.

I hope you enjoy using seaweed developer!

Photograph developed with seasweed by Melanie King
Photograph developed with seaweed by Melanie King
Photograph developed with seasweed by Melanie King
Photograph developed with seaweed by Melanie King
Photograph developed with seasweed by Melanie King
Photograph developed with seaweed by Melanie King

Further Reading on developing with seaweed

Melanie King is an artist and curator with a specific focus on astronomy. Melanie King’s studio is based in Ramsgate, Kent, UK. She is co-Director of super/collider, Lumen Studios and founder of the London Alternative Photography Collective.
Melanie is currently Artist In Residence at the School of Metallurgy and Materials at The University of Birmingham, from 2021 to 2022.
Melanie is a PhD Candidate at the Royal College of Art (2015-2022). She is a graduate of the MA in Art and Science at Central Saint Martins (2013), and the BA Fine Art at Leeds Art University
(2011). She is a lecturer on the MA programme at the Royal College of Art, and on the BA Photography course at the University of West London. She is represented by the Land Art Agency and has prints available for purchase via Argentea Gallery, Birmingham.

4 thoughts on “Bladderwrack seaweed developer for black and white film”

  1. I sumbled upon your article through a link on 35mmc. I would never have thought of doing this sort of thing but will start to experiment within a few months as I have returned to B&W film, (and processing it myself agin too), after 12 years of strictly digital. Thank you kindly.

  2. Just one word: wow! I’m impressed but need to ask: how did you discover or come up with the notion of seaweed as a developer? Have a safe and wonderful year. ☺

    B. Stockwell

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