Color bleach based on sodium persulfate.

¡hola a todos!

Llevo un par de años siguiendo los hilos de este foro y estoy impresionado por el enorme conocimiento que tenéis muchos de vosotros.

Quiero compartir con ustedes un poco de mi investigación. Pido disculpas de antemano por mi inglés, no es mi lengua materna.

He visto algunos hilos aquí donde hablan de alternativas a los blanqueadores Rehalógenos, eso me llevó a investigar algunas patentes y encontré esa patente de Kodak que habla de un par de alternativas basadas en sales de sodio. US5464728A

La patente habla de dos blanqueantes con persulfato, uno que utiliza un acelerador como pre-baño y otro que utiliza un catalizador en la fórmula para obtener un blanqueo rápido y limpio. Esta última fue la fórmula que utilicé. Agregué los químicos en la siguiente secuencia:

Ácido dipicolínico 2,3gr
Nitrato férrico nonahidrato 2,52gr
Ácido acético 2,86ml
hidróxido de amonio 5ml
Persulfato de sodio 29,75gr
Cloruro de sodio 4,37gr

Agua para 500ml

Agregué el ácido dipicolínico, el nitrato férrico y el ácido acético, luego con hidróxido de amonio llevé el pH de la solución a pH 4 y finalmente agregué el persulfato y el cloruro de sodio. Verifique el pH nuevamente y ajústelo si es necesario para tener un pH final de 4.

El ácido dipicolínico junto con el nitrato férrico forman un catalizador que ayuda a acelerar el proceso de oxidación del persulfato. El agente halógeno a utilizar es cloruro, pero en la patente menciona que se puede sustituir por bromuro sin ningún problema, pero por cuestiones de economía se utiliza cloruro. .

Todos los productos químicos son fáciles de conseguir, excepto el ácido dipicolínico. Tuve que conseguir un proveedor que trabajara con Merck para poder comprarle a la marca. Sin embargo, parece que Santa Cruz Biotechnology tiene ácido dipicolínico a la venta en su sitio web, lo cual es conveniente si vives en Estados Unidos.


Probé el proceso Bleach con C41, E6 y ECN-2. Voy a añadir imágenes de muestra de la emulsión y una foto digitalizada, primero C41, luego E6 y al final ECN-2.

¿Qué problema puedo ver? La lejía se vuelve muy ácida con el paso de los días, lo que según la patente puede afectar el persulfato. ¿Cómo crear un buffet más estable, es posible? ¿Qué opinas del orden de la mezcla? ¿es correcto? Dejando de lado todo lo anterior, los resultados resultan ser muy buenos. Te explico el tiempo de cada proceso a continuación:

Proceso C41

Desarrollador 3:15 min.

Detener baño (ácido sulfúrico 1% + bisulfito sódico) 30 seg.

Blanqueador persulfato 3:00 min.

Primer Lavado 1:00 min.

Fijo (sodio) 4:00 min.

Segundo Lavado 2:00 min.

Ascenso final 1:15 min.


Proceso E6

Primer revelador 6:15 min.

Detener baño (ácido sulfúrico 1% + bisulfito sódico) 30 seg.

Lavar 30 seg.

Reexposición 1:00 min. Por lado.

Desarrollador de color 6:00 min.

Lavar 30 seg.

Pre-blanqueo 2:00 min.

Blanqueador persulfato 3:00 min.

Lavar 30 seg.

Fijar (sodio) 4 min.

Ascenso final 1:15 min.


Proceso ECN-2

Pre-baño (Remjet) 2:00 min.


Lavado para eliminar remjet: 3 a 4 cambios de agua hasta eliminar lo mejor posible el remjet.

Desarrollador 3:30 min

Detener el baño (ácido sulfúrico al 1%) 30 seg.

Lavar 1 min.

Retire la película del tanque y del carrete y retire cualquier resto de remjet. Lo volvemos a poner en el carrete.

Blanqueador persulfato (27°C) 3 min.

Lavar 1 min.

Fijar 4:00 min.

Lavar 2 min.

Ascenso final 1:15 min


No me extenderé más, espero vuestros comentarios. Muchas gracias por el tiempo de leerme.

{Moderator edit; translation added in English:}

hello everyone!

I have been following the threads on this forum for a couple of years and I am impressed by the enormous knowledge that many of you have.
I want to share with you a little of my research. I apologize in advance for my English, it is not my native language.

I've seen some threads here where they talk about alternatives to Rehalogen bleaches, that led me to research some patents and I found that Kodak patent that talks about a couple of alternatives based on sodium salts. US5464728A

The patent talks about two persulfate bleaches, one that uses an accelerator as a pre-bath and another that uses a catalyst in the formula to obtain fast and clean bleaching. The latter was the formula I used. I added the chemicals in the following sequence:

Dipicolinic acid 2.3gr
Ferric nitrate nonahydrate 2.52gr
Acetic acid 2.86ml
ammonium hydroxide 5ml
Sodium persulfate 29.75gr
Sodium chloride 4.37gr
Water for 500ml

I added the dipicolinic acid, ferric nitrate and acetic acid, then with ammonium hydroxide I brought the pH of the solution to pH 4 and finally added the persulfate and sodium chloride. Check the pH again and adjust if necessary to have a final pH of 4.

Dipicolinic acid together with ferric nitrate form a catalyst that helps accelerate the persulfate oxidation process. The halogen agent to be used is chloride, but the patent mentions that it can be replaced by bromide without any problem, but for reasons of economy chloride is used. .

All chemicals are easily available except dipicolinic acid. I had to get a supplier that worked with Merck to be able to buy from the brand. However, it appears that Santa Cruz Biotechnology has dipicolinic acid for sale on their website, which is convenient if you live in the United States.

I tested the Bleach process with C41, E6 and ECN-2. I am going to add sample images of the emulsion and a digitized photo, first C41, then E6 and at the end ECN-2.

What problem can I see? The bleach becomes very acidic over the days, which the patent says can affect the persulfate. How to create a more stable buffet, is it possible? What do you think of the order of the mix? it's right? Leaving aside all of the above, the results turn out to be very good. I explain the time of each process below:

Process C41
Developer 3:15 min.
Stop bath (1% sulfuric acid + sodium bisulfite) 30 sec.
Persulfate bleach 3:00 min.
First Wash 1:00 min.
Fixed (sodium) 4:00 min.
Second Wash 2:00 min.
Final ascent 1:15 min.

E6 process
First developer 6:15 min.
Stop bath (1% sulfuric acid + sodium bisulfite) 30 sec.
Wash 30 sec.
Reexposure 1:00 min. Per side.
Color Developer 6:00 min.
Wash 30 sec.
Pre-whitening 2:00 min.
Persulfate bleach 3:00 min.
Wash 30 sec.
Fix (sodium) 4 min.
Final ascent 1:15 min.

ECN-2 process
Pre-bath (Remjet) 2:00 min.
Wash to remove remjet: 3 to 4 changes of water until the remjet is removed as best as possible.
Developer 3:30 min
Stop bath (1% sulfuric acid) 30 sec.
Wash 1 min.
Remove the film from the tank and reel and remove any remaining remjet. We put it back on the reel.
Persulfate bleach (27°C) 3 min.
Wash 1 min.
Set 4:00 min.

Wash 2 min.
Final ascent 1:15 min

I will not expand further, I await your comments. Thank you very much for the time to read me.

Click to expand...

Buenas, nos encontramos también por aqui...

La solución inmediata para hacer el buffer/amortiguador/tampón deseado es añadir la sal básica del acido acético, por ejemplo el acetato de sodio que es fácil de conseguir. Debajo te dejo el link a una calculadora de pH que he encontrado para este sistema. No llega a la cantidad que has añadido de ácido pero se puede extrapolar. Si he hecho bien el calculo, deberías añadir 1,15 gramos de acetato de sodio para un pH de 4 en 500 ml.

Welcome to Photrio @alons98 and thanks very much for sharing your very interesting experiments with all of us! I've added an English translation to your post to make it easier for many of us to access.

The results speak for themselves; evidently, the process works! Does the patent say anything about how the perchlorate bleach might affect the long-term stability of the images?

@halfaman the use of an acetate buffer makes sense at least at first glance; I do wonder if it perhaps interferes with the catalyst. But perhaps it doesn't and it'll work just like that. An acetate buffer is easy to prepare from regular acetic acid and sodium hydroxide. The cited Kodak patent is hopeful, in any case, since it mentions the following:

The bleaching solution may contain a buffer consisting of an organic acid or inorganic acid and/or a salt thereof. Useful examples include phosphoric acid and salts of phosphate, citric acid and salts of citrate, boric acid and salts of borate or metaborate, acetic acid and salts of acetate, and carbonate

Click to expand...

So either an acetate or citrate buffer would be a very sensible choice for the homebrew enthusiast.

I have some sodium perchlorate handy here, but no dipicolinic acid (DPA). I wonder how slow the bleach is without the catalyst. I also wonder how crucial the DPA is or whether it can be substituted with something more easily available. I haven't done a lot of reading yet, but e.g. this patent gives some more clues: https://patents.google.com/patent/US5536625A/en Indeed, there appears to be a range of alternatives that could be explored. The big question of course is whether on balance it will be easier to work with persulfate (easily available) that requires a more outlandish accelerator/catalyst, or to just bite the bullet and use a regular color bleach, which can be easily obtained in most parts of the world, but may be a little more expensive (although it provides excellent economy in my experience).

halfaman said:

Buenas, nos encontramos también por aquí...

La solución inmediata para hacer el buffer/amortiguador/tampón deseado es agregar la sal básica del ácido acético, por ejemplo el acetato de sodio que es fácil de conseguir. Debajo te dejo el enlace a una calculadora de pH que encontró para este sistema. No llega a la cantidad que se ha añadido de ácido pero se puede extrapolar. Si he hecho bien el cálculo, deberías añadir 1,15 gramos de acetato de sodio para un pH de 4 en 500 ml.

https://www.aatbio.com/resources/buffer-preparations-and-recipes/acetate-buffer-ph-3-6-to-5-6

Click to expand...

Es bueno encontrar caras conocidas, ahora que lo pienso quizas te haya visto un par de veces por aquí pero lo olvide por completo mientras escribia esto.

no se que me ocurra con el acetato de sodio, hago desidia por comprar siempre.

Ahora mismo tengo acito acético e hidróxido de sodio, voy a hacer el acetato con eso mientras lo compro! Muchas gracias buen hombre.

koraks said:

Welcome to Photrio @alons98 and thanks very much for sharing your very interesting experiments with all of us! I've added an English translation to your post to make it easier for many of us to access.

The results speak for themselves; evidently, the process works! Does the patent say anything about how the perchlorate bleach might affect the long-term stability of the images?

@halfaman the use of an acetate buffer makes sense at least at first glance; I do wonder if it perhaps interferes with the catalyst. But perhaps it doesn't and it'll work just like that. An acetate buffer is easy to prepare from regular acetic acid and sodium hydroxide. The cited Kodak patent is hopeful, in any case, since it mentions the following:

So either an acetate or citrate buffer would be a very sensible choice for the homebrew enthusiast.

I have some sodium perchlorate handy here, but no dipicolinic acid (DPA). I wonder how slow the bleach is without the catalyst. I also wonder how crucial the DPA is or whether it can be substituted with something more easily available. I haven't done a lot of reading yet, but e.g. this patent gives some more clues: https://patents.google.com/patent/US5536625A/en Indeed, there appears to be a range of alternatives that could be explored. The big question of course is whether on balance it will be easier to work with persulfate (easily available) that requires a more outlandish accelerator/catalyst, or to just bite the bullet and use a regular color bleach, which can be easily obtained in most parts of the world, but may be a little more expensive (although it provides excellent economy in my experience).

Click to expand...

Thank you very much for the welcome, although I am really clumsy, I tried hard to write the thread and ended up publishing it in Spanish, the idea was to do it in English, anyway.

I have not seen in detail, if the patent mentions it, the stability of the dye over time, and the short time that I have been using this bleach does not work to be able to give an answer. time will tell.

I will try to use sodium hydroxide to create a sodium acetate buffer, right now the Bleach I made has been around for 3 weeks and seems to have stabilized, I am still monitoring the pH.

According to what I have read in other forum threads, persulfate is a strong but very slow oxidant, and although DPA implies an extra effort to obtain it, I think it is very worth it. Doing the math, in my country, I can prepare 5 liters of persulfate bleach with the same amount of money as 2 liters of commercial bleach, all because of thinking about the possibility of a commercial chemical shortage.

Interesting, but seems pointless in my region. Finding this dipicolinic acid will not be easy.
Is there an objective reason to use chloride instead of bromide? Wouldn't there be better capacity with bromide?

hello
There is a formula I use based on persulfate oxidation of hydroquinone into quinone. It works for both E6 and C-41 films

H2O 800ml
Sodium Acetate 5g
Pot.Persulfate 10g
Pot. Bromide 20g
Copper Sulfate 1g
Glacial acetic acid 15ml

once mixed add

Hydroquinone 1g
the blue solution will turn a brilliant apple green
addH2O to 1000ml
the solution needs to age over night before use and seems to last about 2 weeks(turns brown when goes bad)
It is NOT friendly to eyes (or anything else)so open trays are not something I would use

lamerko said:

Interesting, but seems pointless in my region. Finding this dipicolinic acid will not be easy.
Is there an objective reason to use chloride instead of bromide? Wouldn't there be better capacity with bromide?

Click to expand...

The patent mentions that chloride is used for economic reasons, but that it can perfectly be replaced by bromide.

R Paul said:

hello
There is a formula I use based on persulfate oxidation of hydroquinone into quinone. It works for both E6 and C-41 films

H2O 800ml
Sodium Acetate 5g
Pot.Persulfate 10g
Pot. Bromide 20g
Copper Sulfate 1g
Glacial acetic acid 15ml

once mixed add

Hydroquinone 1g
the blue solution will turn a brilliant apple green
addH2O to 1000ml
the solution needs to age over night before use and seems to last about 2 weeks(turns brown when goes bad)
It is NOT friendly to eyes (or anything else)so open trays are not something I would use

Click to expand...

I have seen this formula before and I have it saved to use one day, thanks! however I consider it somewhat dangerous. It was presumptuous of me to say that the persulfate bleach that I published works for E6, I have said that it is very destructive with color dyes, it is better to use a weak EDTA-based bleach, there is a functional and simple one here in the forum, I am already using it, I only use this persulfate bleach with C41 and ECN-2. and with the dipicolinic acid-Fe catalyst I have no risk of corneal detachment.

It is not the most friendly bleach, true .
I started using it maybe 20 years ago when I found the cost of the kodak bleach alone was as expensive as the other components of the development kit . So far the slides I ran back then look as good today as they did back then. At least for me using a rotary development setup allows me to minimize my exposure. One day I would like to try mixing up some edta bleach, if I found a decent formula

Robert