Quote Originally Posted by wogster View Post
Washaid is a hypo eliminator ...
Your conclusions about when to use wash aids are right on, but I have a problem with the term "wash aid" being characterized as synonymous with "hypo eliminator". They are not at all the same.

I know it sounds rather nitpicky, but I hope the terminology of wash aids and hypo eliminators becomes better understood and used since all these terms can be so confusing to beginners under even the best circumstances.

Wash aids like Kodak Hypo Clearing Agent are not hypo eliminators; the sulfite based wash aids are merely aids to wash hypo out of the paper.

Hypo eliminators are completely different; they destroy hypo within the paper rather than helping it be removed from the paper. Recent research suggests that hypo eliminators may actually be detrimental. It has not been fully studied, but total elimination of hypo may make for a less permanent print. Research suggest that an infinitessimal amount of hypo needs to be retained for best permanence. I do not know why. How much residual hypo? About what remains after a thorough washing using wash aids and plenty of clean water.

Wash aids are rather gentle in effect, merely allowing better diffusion of water and chemicals in and out of the paper base.

Hypo eliminators are rather different, much more aggressive chemically, and must be used with restraint, after the majority of hypo has been already removed through normal washing procedures(with the prior help of wash aids). I'm no chemist but if I get it right, a strong enough eliminator to destroy all the hypo would also seriously attack the image.


According to Ryuji Suzuki in http://wiki.silvergrain.org/wiki/Washing_aid :
"Hypo eliminator usually refers to a solution containing hydrogen peroxide or peroxide-releasing compound such as percarbonate, perborate or persulfate. These solutions may also contain ammonia, other alkaline agents, bromide, iodide, and other additives.

The idea behind hypo eliminator is to oxidize thiosulfate to harmless compounds that are not adsorbed by silver surface. However, it was later found that peroxide solutions damage and undermine image-forming metallic silver. Today, the use of hypo eliminators are discouraged."