# Novel method of film stripping?



## rickbb (Sep 29, 2013)

Has anyone tried this method?

http://journals.tubitak.gov.tr/chem/issues/kim-03-27-1/kim-27-1-17-0109-1.pdf

From what I read you strip in NaOH normally, and then raise the temp to just under boiling and stir for 1 1/2 hours and the gelatin will dissolve and drop the metallic silver out.

Unless I'm not reading this right it would seem to be better than incinerating the sludge to get rid of the emulsion to recover the silver.


----------



## meatheadmerlin (Jan 19, 2017)

I have a small amount of exposed, but not developed, black and white 35mm film.
Rather than buy a whole bottle of thiosulphate fixer to strip the film of silver-halide easily, I was researching alternative methods for removing it.

This article gives two fixer alternatives: household ammonia, or table-salt solution.
http://caffenolcolor.blogspot.com/2012/03/alternative-to-fixer-bath.html

I have read here about the potential dangers of not properly neutralizing solutions of ammonia and silver.
So, I tried the salt solution on a small piece of the film.
It showed visible progress on the emulsion in less than 24 hours, and I left it in for a few days after that.
The film still need a little scrubbing to actually remove the emulsion completely from the plastic, but it did all come off.
From my results, I question the salt solution's utility as a proper fixer for photography processing, but that may depend a lot on the concentration and length of time it sits in the solution.

I have seen it alluded to in other random forums that common household bleach can be also used to strip film, as well as pool bleach.
This video says it uses diluted household bleach to strip rear emulsion from X-ray film sheets.
However, there are few details and the film shown in the process doesn't appear to be a standard X-ray, rather a landscape scene negative.
https://www.youtube.com/watch?v=gnws-vaAD0U

I have yet to try household bleach, but will post my findings here.

(edit: fixed link)


----------



## rickbb (Jan 20, 2017)

Bleach works well for small amounts of film. The action of dissolving the protein based emulsion converts the bleach into lye and the reaction slows dramatically. Many methods use lye with bleach added to speed up the stripping process. 

These are well known processes and the forum has lots of posts/information on them. 

The last batch of x-ray film I did, (2 years ago as my last source finally went digital), I took the stripped sludge and put it in straight bleach to do a final dissolve of the remaining emulsion. Then was able to do a wash and filter to get clean silver salts without having to roast off any emulsion.


----------



## Topher_osAUrus (Jan 20, 2017)

Juan Manuel has numerous posts on the subject matter.

This is one that mentions a method you omitted
http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=37&t=3282&p=27868#p27868

I have no hands on experience with film yet, but if the oxalic method is not to your taste, between this link
http://goldrefiningforum.com/~goldrefi/phpBB3/search.php?st=0&sk=t&sd=d&sr=posts&author_id=3554&start=660
and this next one, you should hopefully find the answers you seek
http://goldrefiningforum.com/~goldrefi/phpBB3/search.php?keywords=silver+film&terms=all&author=goldsilverpro&sc=1&sf=all&sr=posts&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

You mention bleach, but it produces a "silver intermediate compound that needs more processing to obtain pure silver"
The product from oxalic can be melted to silver metal according to Juan.
Oxalic acid can be found as wood bleach under the brand name savogran.


----------



## eaglewings35 (Jan 20, 2017)

rickbb said:


> Bleach works well for small amounts of film. The action of dissolving the protein based emulsion converts the bleach into lye and the reaction slows dramatically. Many methods use lye with bleach added to speed up the stripping process.
> 
> These are well known processes and the forum has lots of posts/information on them.
> 
> The last batch of x-ray film I did, (2 years ago as my last source finally went digital), I took the stripped sludge and put it in straight bleach to do a final dissolve of the remaining emulsion. Then was able to do a wash and filter to get clean silver salts without having to roast off any emulsion.


Hey Rick,
I've been doing some stripping of totally green industrial x-Ray film.
I bought some thiosulfate to strip the silver and emulsion from the plastic film.
Then I use HCl to convert the suspended silver to silver chloride, then I use iron (nails) to convert it to silver metal. The problem I've been having is at the end of the conversion. The silver chloride has converted to the fluffy grey (concrete color) silver material that is ready for washing and melting. Now for the problem area..... after I do several HCl rinses to make sure the iron is all gone, then I do several boiling water rinses.
I put the silver mud in the oven to dry it. Once I get it out, it has turned black.
Is this the result of the protein emulsion that coats the silver on the film? How is the protein emulsion dealt with? It affects the melt too. It causes a nasty smell, and even nastier melt,
Leaving a black layer on the silver. What's your take on this?


----------



## Topher_osAUrus (Jan 20, 2017)

Silver Sulfide I would imagine


----------



## meatheadmerlin (Jan 21, 2017)

For Oxalic Acid, I was going to mention Bar Keepers Friend, but according to the MSDS it only contains 7.5%-9.5% by weight.
It also lists Felspar and Linear Sodium Dodecyl Benzene Sulfonate(DDBSA), so probably not very desirable.
https://www.barkeepersfriend.com/wp-content/uploads/2015/12/SDS_BKF_Cleanser_Polish_6-12-15.pdf

The Savogran website also lists an Oxalic Acid Marine Cleaner, which appears to be a relatively new product, in addition to its Concentrated Wood Bleach. Both are shown on this page, with MSDS links.
http://www.savogran.com/patch-and-repair.html

Both products' MSDS refer to them as wood bleach, and list the Oxalic Acid (dihydrate) content at 95%-100%, but the have different revision dates and slightly different content.


----------



## rickbb (Jan 25, 2017)

eaglewings35 said:


> rickbb said:
> 
> 
> > Bleach works well for small amounts of film. The action of dissolving the protein based emulsion converts the bleach into lye and the reaction slows dramatically. Many methods use lye with bleach added to speed up the stripping process.
> ...



You appear to have mixed up bits and pieces from several different methods. Stop. You are making it hard on yourself. Recovery of silver from x-ray film is simple, labor intensive, but simple.

Thiosulfate only dissolves the undeveloped silver, not the emulsion so you should not have any in your mud to worry about. It will not dissolve any exposed and developed film either, you will need a different method if you get any of that.

If you have sufficient volume of film you should look at either buying or making an electrolytic recovery unit. It will plate out the silver directly from the thiosulfate as almost pure metallic silver ready to wash, dry and melt. A good setup will run automatically allowing you to do other things. If you have a good steady supply of film it will pay for itself very quickly, trust me. 

If not then you can drop the silver from the thiosulfate with iron, zinc or copper. That dropped "mud" is silver sulfate, take that well washed mud and put in a solution of lye and slowly add corn syrup with continuous stirring, (this will stink to high heaven, but it's not toxic just smells like it). That will convert the silver sulfate into metallic silver. Thoroughly wash that mud, dry and melt.

You don't use HCL and iron to convert silver chloride to metallic silver, you use sulfuric acid and iron, (nails). I'm not sure you even had silver chloride to start with, you had silver sulfate and put that in HCL, maybe that made it silver chloride, I don't have enough chemistry background to know if works that way. But, you don't need to do this step in the first place so don't do it.

If it's fluffy gray it's not metallic silver it's possibly silver chloride and if you try and melt that directly you will lose some silver and make some noxious gasses in the process as well. 

You can melt it, if you want to, but you need to add some flux, a pinch of borax and sodium carbonate. That will be a gray green mass on the silver button/bar that you can knock off with a hammer. But if you simplify your process and make actual metallic silver in the first place you won't need to do this either.

I don't know what that black layer is your getting, doubt it's any part of the emulsion as you shouldn't have any in the mud. I suspect it's an artifact of blending parts and pieces of different, (and not compatible), processes. That smell you are getting when you melt silver chloride is a toxic gas, hope your doing this outside and you stay upwind of it.


----------



## eaglewings35 (Jan 25, 2017)

Hey Mr Rick,
Well, the process I am using is this.....
I take the crystal clear thiosulfate (after it is completely saturated with silver)
and add HCl..... This converts the suspended silver into silver Chloride (AgCl) which is white as snow.
I siphon off the used fixer and wash thoroughly.
Then I add some more HCl add iron (nails). This takes it to silver metal.

I have done the Karo method, and it goes from AgCl to silver Oxide, then to silver metal.
I skip the Oxide part and go straight to the metal part.

The emulsion is what binds the silver "bars" together in a straight line, which makes them react to light.
What I am having a problem with is the AgBr, or Silver Bromine. The bromine is what is turning black and sticking around.
I sent a sample off to Lazer Steve, and he had an extremely hard time trying to get rid of it.

I have been doing some research in Wiki, and I found out that Bromine is completely insoluable in water or acids. But Ammonia does dissolve it somewhat. So, I am going to try to do a hot boil in ammonia to see if this dissolves the bromine.
Also, I have a man that is selling me an electrolytic unit for $100.

My question here is... will plating it in the cell affect the bromine differently, hopefully causing it to turn loose?

Thanks Rick, I have read most of your post on this subject and it is a pleasure picking your brain.
Regards,
Kerry


----------



## Topher_osAUrus (Jan 25, 2017)

Im not sure if HCl + Iron will convert silver chloride?
Do you have a reference you could share for that method?

I know sulfuric and iron, or HCl and zinc, or HCl and aluminum.
As well as the NaOH and sugar method, or NaOH then dissolve the silver oxide in nitric and cement.

Also, ammonia will lose its potency when being heated, since its a gas dissolved in water.


----------



## rickbb (Jan 26, 2017)

Don't use ammonia on silver, if you aren't careful and know exactly what you're doing you could hurt yourself, badly.

If your getting a electrolytic unit then you won't need any further wet chemistry. You will get 97% purity silver bars or better with just 3 simple steps. Skip all the HCL, iron, and so on.

Strip film in thiosulfate,
plate out silver,
melt into bars.


----------

