What is salt stabilizing a salt print

[kevin klein]

Although I have been mostly using cyanotype for printing negatives I use salted paper for some smaller work. I have read about placing the exposed print in a salt solution, what does this do, is it first done before rinsing or after, I have seen it referred to both ways.

 

[Mainecoonmaniac]

I'm not a chemistry expert, but I think you need sodium with silver nitrate together for the paper to be light sensitive during your exposure of your print. Sodium is the halide that makes the silver light sensitive. Correct if me I'm wrong.

 

[removed account4]

hi kevin
i hope cliveh responds to your post!
the original "fixer" talbot used was a saturated salt bath
cliveh has experience with using this ...

 

[NedL]

Clive can tell us about using salt to stabilize a print instead of hypo to fix it ( which is very interesting and worth a whole thread by itself! ). I think Kevin is referring to recommendations of a salt bath before fixing in hypo.

The salted paper print starts with some excess silver nitrate. The idea of the salt wash is to convert any remaining silver nitrate to silver chloride, so that it can be removed in the hypo. If there is still silver nitrate on the print when it goes into the hypo, it can cause stains, and it will decompose the hypo sooner.

You are absolutely correct that some instructions put the salt wash first and some put it after a water wash. Not only in modern descriptions of salt printing but in historical descriptions as well. Some instructions leave out the wash in salted water completely.

I've tried it every way. When I first started, I just washed in water and then fixed. Later, I read Chris James' book and started using the salt bath as the first step. These days I usually "pre-wash" in water to remove most of the silver nitrate, then a brief 3 minute dip in salt water to convert what little silver nitrate remains to silver chloride, and then an extended water wash before fixing.

There's also some controversy or inconsistency about how strong the salt bath should be. I've been using a "pinch" of salt like James recommends, but many people use a much stronger solution ( 2% or even 10 or 15% ). I think most of these differences come from different ways of proceeding. If you don't pre-wash in water, there will be more AgNO3 to convert, so a weak salt solution might not be enough to convert it all, especially if it's sunk into thick paper. Also the amount of excess silver will depend on a lot of factors, like whether you double coat, what kind of binder, how thick the paper is, etc.

Most of the time, with thin papers at least, I have not seen any difference between these different approaches. A good water wash, or 1st in salt then water, or 1st in water and then in salt all can work well with no staining. Where it could matter is if you are having trouble. I don't want to write a whole book here, but depending on the cause of the stain, one washing approach might work better than another. But always the first thing to try is longer washing!

 

[kevin klein]

Thanks Ned, your way of presoaking first sounds logical,I will go that way, thanks again.

 

[pdeeh]

There's a discussion in this thread : (there was a url link here which no longer exists)

 

[kevin klein]

Thanks pdeeh, that gives a lot to work with. I got the idea of trying to fix a collodion plate with a strong salt solution to see what happens.

 

[Dibbd]

...The idea of the salt wash is to convert any remaining silver nitrate to silver chloride, so that it can be removed in the hypo...

Why would you need to do that? Silver nitrate is soluble in water. It should go away in the wash anyway.

Just yesterday I was in Bradford at the National Media Museum looking at Fox Talbot's original prints. The very early, salt fixed, ones are not on display because they are still sensitive to light but they have digital reproductions of them including the latticed window and it's negative.

 

[NedL]

Talbot's salt-fixed prints are a different ( and interesting ) story. A topic deserving it's own thread.

What's being discussed here is whether it is a good idea to use a salt bath prior to fixing in hypo. As Kevin noticed, the advice about this is inconsistent over the years. I suspect the different experiences with it came from differences in the way people worked. For example, some people double coat the silver nitrate sensitizer, and many early printers sensitized their paper by floating the paper on a solution of silver nitrate. Either of these approaches can lead to a large excess of silver nitrate in the paper, and not just near the surface of the paper where the sliver chloride has formed, but deep inside the paper and in contact with any internal sizing, where it could be difficult to wash out. Other people tune the silver nitrate sensitizer so that there is only a little excess, perhaps close to the surface of the paper where it can be more easily washed out with water.

Why would you need to do that? Silver nitrate is soluble in water. It should go away in the wash anyway.

I agree with you. The reason usually given is that even tiny amounts of silver nitrate that do not wash out can react with the hypo and cause brown silver sulfide stains. The logic is that it is better to convert all silver nitrate to silver chloride first, which is soluble in the hypo and makes silver thiosulfate products that are soluble in water. I don't think I've seen this brown staining problem, but I don't doubt that the people recommending a salt bath have seen it. Maybe they used a lot of excess silver nitrate and a paper that was difficult to wash. A soak in salt water is easy enough, so it seems to me that it could be insurance against incomplete washing.

Having said that, I'll touch on something I was trying to avoid in my previous post. I have seen examples of internal stains that appear with either kind of washing and not the other. These are grey, not brown, so probably not the same kind of stain the salt bath advocates are worried about. With the water wash first, we're not only washing the AgNO3 out of the paper, but could also be allowing some of it to migrate from the surface down through the paper and come in contact with the paper's internal sizing, where it could react and cause stains. Alternatively, if there is a lot of excess AgNO3 and we soak it in a salt bath first, silver chloride might form underneath the surface sizing, where it is difficult for the hypo to get to and difficult to wash out the silver thiosulfate products if it does. So the physical properties of the paper and the sizing can make all of this not work as well as we hope.

Salt printers get obsessed with paper, and different papers really do behave differently in all sorts of ways.

 

[kevin klein]

So what is being said is the thickness of the paper and sizing can make a difference in how well the silver washes out, correct? I try to use the thinnest I can find.