fixer question

I do wet-plate tintypes and ambrotypes. Of course, the ideal fixer is P.Cyanide; but when I go to events, bringing kcn is not a good idea. I've been using Sod. Thiosulfate and washing in tub of water for 20-30 minutes. I'm still worried about residual thiosulfate; so here is my question.... How effective would it be for me to possibly use ammonium thiosulfate with hypo-clear? Can hypo-clear be used with ammonium thio.? If I use hypo-clear and keep it in a pan, how many times can I use it before replacing?
Is ammon. thio. more soluble in the wash than sodium thio.?

Thanks for your time, Ty Guillory

Ty G said:

I do wet-plate tintypes and ambrotypes. Of course, the ideal fixer is P.Cyanide; but when I go to events, bringing kcn is not a good idea. I've been using Sod. Thiosulfate and washing in tub of water for 20-30 minutes. I'm still worried about residual thiosulfate; so here is my question.... How effective would it be for me to possibly use ammonium thiosulfate with hypo-clear? Can hypo-clear be used with ammonium thio.? If I use hypo-clear and keep it in a pan, how many times can I use it before replacing?
Is ammon. thio. more soluble in the wash than sodium thio.?

Thanks for your time, Ty Guillory

Click to expand...

There is a lot of confusion about fixers and washing. For modern B&W silver photography the most commonly used fixers are either ammonium (rapid) or sodium (standard) thiosulfate based products. The only real difference between the two is the speed of the process. The ammonium thiosulfate based products being the faster of the two, hence the "rapid" moniker. Either form of the thiosulfate can be formulated into an alkaline, neutral, or acid fixing bath. A hardening agent, usually alum, is sometimes incorporated into the bath which requires the formula to be acidic. It is the acid and hardener that make removal of the residual hypo difficult. Fiber based papers are particularly difficult to clear because the fibers in the paper act like a sponge and want to hold on to all that solution. Films, resin coated papers, and certainly glass plate will not hold on to excess fixer and they wash out fairly quickly on their own. No harm is done by using a hypo clearing agent after any type of fixer, but it is not necessary for anything other than fiber based papers.

There is a lot of confusion about fixers and washing. While fschifano got it mostly right above, it is also true that ammonium thiosulfate fixers wash out of the emulsion as well as the paper faster than non-rapid fixer of otherwise identical composition and adjusted to the same pH.

In the case of gelatin dry plate, the washing of the plate can be 10 minutes washing in plain water, but I'm not sure if the washing of the thiosulfate and silver-thiosulfate complex ions is just as fast in tintypes and ambrotypes. There can be a significant difference depending on the binder.