Edwal 4+1 Hypoclear

[timbo10ca]

Is this similar to other chemistries in regards to shelf-life (i.e about 6 months after opening), or is it more like selenium toners (which have a much longer shelf-life)?

Thanks,
Tim

 

[Tom Hoskinson]

Based on the Edwal 4&1 Material Safety Data Sheet (MSDS), it should have a long shelf life. Based on the chemical ingredients listed in the MSDS, I would call Edwal 4&1 a Wash Aid, Not a Hypo Eliminator.

See: Dead Link Removed Edwa 4&1

 

[Michel Hardy-Vallée]

Based on the Edwal 4&1 Material Safety Data Sheet (MSDS), it should have a long shelf life. Based on the chemical ingredients listed in the MSDS, I would call Edwal 4&1 a Wash Aid, Not a Hypo Eliminator.

See: Dead Link Removed Edwa 4&1

What is the difference between a wash aid and a hypo eliminator? Aren't those synonmys for products getting rid of the thiosulfate compounds in photographic materials?

 

[bob01721]

What is the difference between a wash aid and a hypo eliminator? Aren't those synonmys for products getting rid of the thiosulfate compounds in photographic materials?

As I understand it, hypo clearing agents react with the intermediate compound created by fixing and convert it to the final compound rapidly. Not usually required with a rapid-fixer, but sometimes used with the non-rapid (?) type. Wash aids are surfectants (surfactants) which help the water "sheet" off the film while drying.

 

[Michel Hardy-Vallée]

I think I have my answer...

From Grant Haist, "Modern Photographic Processing"

"Thiosulfate elimination can be accelerated by the use of two classes of chemicals: (1) compounds that act by physically displacing the thiosulfates from the photographic material by an ion-exchange action and (2) compounds that react with the thiosulfate, usually oxidizing it to a form that is more soluble or more diffusible during the subsequent washing in water. The first class of compounds, which do not react chemically with the thiosulfate, are usually called hypo clearing compounds or washing aids. The second class of compounds, the oxidizers, are called hypo eliminators [Note from Haist: the term "hypo eliminator" usually referes to chemical treatments that oxidize the thiosulfate]. Both types of compounds have as their objective the improvement of silver image permanence by the reduction of the quantity of silver thiosulfates and thiosulfate that is retained by the photographic material." (v1, p. 648)


MSDS for Kodak HCA:
Dead Link Removed

Key ingredients in working solution:
Sodium sulfite 1-5%
Sodium bisulfite < 1%

MSDS for Edwal HE:
Dead Link Removed

Key ingredients in working solution
Ammonium sulfite 5%
Sodium sulfite 1.6%

Sodium sulfite is from the class of (1) hypo-clearing agent, and is present in both products. As for ammonium sulfite, I can't find an exact mention about it in Haist. I suppose it behaves as a hypo-clearing salt, but someone with more chemistery experience than I might know.

Real hypo-eliminator formulas like Kodak HE-1 do not use sulfite compounds. HE-1 uses hydrogen peroxide and ammonia in water solution.

There is no difference between a "wash aid" and a "hypo clearing agent" in Haist, so I suppose Tom is using these terms as synonyms. However there is a difference between "hypo clearing" and "hypo elimination." Edwal's product therefore seems to belong more to the hypo clearing category, despite their "hypo eliminator" brand name.

Sorry for the tangent!

 

[Tom Hoskinson]

Yes, I treat Wash Aid and Hypo Clearing Agents as synonyms.

Ammonium sulfite works as a washing aid and is used in Perma Wash and Edwal 4&1.

Hypo Eliminators that employ hydrogen peroxide and ammonia are potentially damaging to the image silver.

 

[Michel Hardy-Vallée]

Another note from Haist: "Any gelatin image on a waterproof support can be freed completely from the thiosulfates by washing in water without the use of a hypo eliminator. With photographic prints on paper base, however, washing, no matter how thorough, can never remove all the thiosulfates retained in the baryta layer (if present) or adsorbed by or held within the paper fibers of the base. For paper prints a hypo eliminator of the ammonia-peroxide type is necessary to achieve the optimum stability of the image." (v1, 660)

Then he notes that these eliminators can cause a slight change in tone, which would be corollary to their potential damaging effect on the silver image.

I would be curious to know what the conservation scientists have discovered about residual thiosulfates since 1979, though.

 

[timbo10ca]

Michel, as usual, you are a wealth of information