Quote Originally Posted by Photo Engineer View Post
Now for finishing, you are using thiocyanate + gold. Here is the order of use timewise from early days to modern:

Active gelatins > Allyl Thiourea > Thiourea > Thiocyanate > Sodium Thiosulfate

Gold was used after about 1945 at Kodak with all of the above, but hypo was used exclusively for Sulfur sensitization since the 50s or 60s.
Ron-- since you're discussing sulfur+gold again, I was wondering why there was such a progression in the use of sulfur compounds over the years. Any ideas as to why thiosulfate was not used from the beginning?

Sheppard in his patent (#1623499) mentions that "sodium hyposulfite" can be used, but then immediately says that this compound is in name correct in the scientific sense and not the compound with the same name used by photographers which is sodium thiosulfate...

By hyposulfite, if he means salts in the archaic system where it's sulfite (SO3=) but with one less oxygen (making SO2=), then (As taken from wikipedia): "However salts containing SO2= and the corresponding acid, hyposulfurous acid (H2SO2) are not believed to exist." - then what would he have been referring to?

OK - I guess I can see it in my 1932 CRC Handbook - it has NaHSO2 and calls is sodium hyposulfite. But I think this is what is called sodium dithionite - not to be confused with sodium dithionate, Na2S206.

So why did he miss thiosulfate in the original patent. He sure listed a lot of other compounds, it seems like thiosulfate would have been something to try, and something they had at hand, too.