Can anyone tell me the chemistry behind how these two products work??

-- ricardo (ricardospanks1@yahoo.com), May 17, 2001

Answers

Hypo clearing agents are washing aids that work mainly by improving the swelling of the gelatin by increasing its pH value, as well as by ion exchange. Any mild alkali, such as sodium carbonate, or sodium sulphite, can be used, the latter being more efficient as it does not only raise the pH but also exchanges with the hypo.

Hypo eliminators, on the other hand, are oxidizing agents that oxidize thiosulphate to sulphate which is easier to wash out of the emulsion and paper. One recipe is ammonia with hydrogen peroxide, which are mixed immediately before use. Hypo eliminators, while recommended in the past, are not considered advisable any more, as their aggressive action may harm paper and image silver.

Regards, Thomas Wollstein

-- Thomas Wollstein (thomas_wollstein@web.de), May 18, 2001.

Ricardo:

I would like to add one small thing to what Thomas has said. The term "hypo eliminator" is oftentimes misused today. I believe that there is one hypo clearing agent sold today (Is it Edwal's?) that is called Hypo Eliminator. It is not the same as Kodak's old hypo eliminator formula that contained ammonia and hydrogen peroxide. This type of thing can lead to confusion, so we need to be careful about what manufacturers mean when they misuse such terminology.

-- Ken Burns (kenburns@twave.net), May 21, 2001.