Bellini presented a film developer without health or environmental hazards

[Law251]

As Paracelsus said: The dose makes the poison. The toxicity of a product is not derived from its ingredients only but also from its concentration. Phenidone and derivatives are used in very small quantites for photographic purposes, a typical formula uses around 0.2 grams per liter.

By the way, the data is relative to the fresh product. A totally exhausted standard metol-hydroquinone developer has very low toxicity in comparison.

Many thanks but I do have a couple more questions: (1) In what way does dimezone differ from metol? My impression is that they are related in some way. (2) Ecofilm is marketed as an alternative to Extol, yet Extol contains ascorbic acid, so how can they be compared?

 

[halfaman]

Many thanks but I do have a couple more questions: (1) In what way does dimezone differ from metol? My impression is that they are related in some way. (2) Ecofilm is marketed as an alternative to Extol, yet Extol contains ascorbic acid, so how can they be compared?

They are related but the same way they are to catechol or hydroquinone. They share a similar chemical structure with an aromatic ring bonded to different chemical groups resulting in very different development activity and interactions.

Ecofilm is marketed like a sort of "liquid XTOL", both containing phenidone and ascorbic acid as development agents.

 

[Law251]

They are related but the same way they are to catechol or hydroquinone. They share a similar chemical structure with an aromatic ring bonded to different chemical groups resulting in very different development activity and interactions.

Ecofilm is marketed like a sort of "liquid XTOL", both containing phenidone and ascorbic acid as development agents.

Thanks again for the info. I have a couple of bottles of Ecofilm and will be running some films (HP5+, FP4+ and D100) through it later in the year and looking forward to seeing the results.

 

[Rudeofus]

Many thanks but I do have a couple more questions: (1) In what way does dimezone differ from metol? My impression is that they are related in some way. (2) Ecofilm is marketed as an alternative to Extol, yet Extol contains ascorbic acid, so how can they be compared?

They are related but the same way they are to catechol or hydroquinone. They share a similar chemical structure with an aromatic ring bonded to different chemical groups resulting in very different development activity and interactions.

Dimezone-S and Metol differ a lot more than Catechol and Hydroquinone. They do serve similar purposes, i.e. they both act as primary development agents, but that's about as far as their similarity goes. Their required concentrations, their behaviors without s secondary dev agents, their interactions with sulfite are quite different.

Dimezone-S:

• does not develop on its own, at least not to normal contrast. Nope, POTA is not a counter argument.
• in its oxidized form is neither restored nor scavenged by sulfite.
• is also not used up in the process. It forms a very stable radical with that one missing electron, and it patiently waits for that electron until a suitable secondary developer molecule floats by.
• does not form insoluble complexes with HQ and is therefore suitable for liquid developer concentrates
• gives you a half stop film speed advantage over Metol, if everything else (sharpness, grain) is kept the same.
• is quite insensitive to bromide build up in developer. This contributed to initial accusations "gives lower sharpness", which could be only overcome by reformulating developers.
• has a very different chemical structure than Metol. Both have a benzene ring, but for Metol this benzene ring plus its two substitutions do the actual work, whereas for Dimezone-S the main job is done by a heterocyclic ring with substitutions, and its benzene ring only dangles off that heterocyclic ring like ballast.