The Daguerreotype: Contemporary work by Jonathan Danforth

Reader Tyler writes:

I read your post, here is some info on one of the questions:

Sodium thiosulfate or sodium hyposulfate is just fixer, they refer to it as Hypo in old books. We can thank Sir John Herchel for it, prior to fixer being around they used salt water to fix dag plates and calotypes. Modern fix is pretty much the same stuff but they add other things to it to harden emulsion on film and work faster and smell worse.

I posted a new dag on my site, on my blog, check it out if you have time, I am making a suite of images that are about suburban manhood.

Thanks again for sharing your knowledge, a lot of your advice for dag making has been pretty useful.

blog.tylerrobbins.net

Tyler

I have seen the chemical Na₂S₂O₃ variously referred to as Hyposulphate of Soda, Hypo, Hyposulphite of Soda, Sodium Pentahyrdate (which is actually Na₂S₂O₃+ 5H₂O), thiosulphate of soda, &c. You’re quite right, Tyler, that John Herschel is the reason for our using this delightful chemical reaction today.

Those of you with inquisitive dispositions might find yourself wondering (depressingly) what makes Sodium Thiosulfate do what it does to daguerreotypes is the process of fixing.

The last sulfur atom in the S₂O₃^2- molecule binds readily to silver (among other things). So in fixing when presented with silver halides such as AgBr (in the case of traditionally-made daguerreotypes), or AgI in Becquerel daguerreotypes, the Hypo removes the undeveloped silver halides from the plate in this delightful exchange of matter:

S₂O₃^2- + AgBr(s) AgS₂O₃^- + Br^-
S₂O₃^2- + AgS₂O₃^- Ag(S₂O₃)^3-

After all THAT happens you can wash it away with the hose. Make sure to wash your hands while you’re at it.

This is the same reaction that takes place in (fewer and fewer) darkrooms all over the country for processing black and white film and prints.

If you happen to work with Iodine with any frequency or if you’ve just soiled your bed linens from the Betadine after a recent surgery, you can use Sodium Thiosulfate to take the stains out of your clothes. Oh and if you’re a sculptor then you can use it with some other goodies for a nice blue-green patina on your bronzes. It’s also a handy de-chlorinator! With all these uses, you might wonder Hypo makes a good dessert topping; it does NOT make a good dessert topping.

Jonathan