POTA (phenidone) capacity

[pasiasty]

What is capacity of phenidone-based developer, e.g. POTA (30‰ sodium sulphite, 1.5‰ phenidone)? I know it's quite unstable and cannot be stored, but I'm curious how many films (e.g. 8x10") might be developed in given amount of developer.

 

[jochen]

Hello,
I would look into the product description of similar commercially available low contrast developers for microfilms. Their capacity should be similar. Normally they are used as one shot developers only for one 35 mm film in 250 ml to 500 ml solution depending on the volume of the tank. Than you can calculate the area in cm² of one sheet 8x10'' and one 35 mm film.

 

[Rudeofus]

There are different ways to achieve low contrast: POTA and its derivatives use a development agent which sticks to silver even in its oxidized state and which therefore inhibits further development. Other low contrast developers, especially those in the film developing cookbook, rely on developer exhaustion, and these can be expected to give very different results if the film area to be developed changes. Therefore one can not trivially extrapolate from one low contrast developer to the other unless you know they are very similar in composition.

About POTA's capacity: I am not aware of published data, but allow me to speculate:The more film area you manage to develop with a given amount of developer, the more agitation I would expect in order to evenly develop the whole area. One roll of 135 film can be in 250ml with inversion tank processing, which requires less agitation than two rolls of 135 film in 250ml in a rotation tank processor. The problem with agitation is that it causes more aerial oxidation, something POTA is very prone to anyway. Unless you positively know that POTA is recommended for rotary processors, I'd recommend inversion tank processing, which imposes an upper limit on the amount of film you can process with a given amount of developer.

 

[Murray Kelly]

Just to point out the quantities are 30g and 1.5g per litre not percent. In fact you'd be pushing to get 30% sulphite into solution as a sodium salt.

 

[Rudeofus]

Just to point out the quantities are 30g and 1.5g per litre not percent. In fact you'd be pushing to get 30% sulphite into solution as a sodium salt.

pasiasty used the ‰ sign, which denotes per mille, not percent. His numbers are 100% (or 1000‰) correct, although most people nowadays would use g/l instead.

 

[pdeeh]

wow I hadn't noticed that, and can't remember ever having seen it before.

(scuttles off to wiki)

 

[Gerald C Koch]

The OP does not state his intended purpose or film to be used. So this is sort of a shotgun reply. POTA was designed to record extreme brightness ranges. It will record an 18 stop tonal range. When used with a film intended for pictorial use POTA produces a VERY LOW CONTRAST negative. It's primary use is now with high contrast films like microfilm to produce a continuous tone negative.

Since POTA is intended for single use I have never seen any capacity figures. Based on other single use developers it should be possible to develop 8 films per liter if the second set (4 films or equivalent) is developed immediately after the first. However this is only an educated guess and testing should first be done.

 

[Rudeofus]

Gerald, POTA is very sensitive to aerial oxidation, since Sulfite does not protect Phenidone (see one of the articles I sent you). The extremely short working solution shelf life of POTA (1 hour is less than 1/4000 of the 6 months stated for D-76 and Xtol) shows this as well. Therefore I would rather advise against the reuse of POTA, even if one run immediately follows the previous run.

 

[pasiasty]

I use POTA to develop very contrasty film, Wephotha FO5 (kinda re-make of ORWO F05), originally intended for line-art reproduction. Sheet film, tray development. I'm really aware that live-time of the solution is in hours if not in minutes. 'Reuse' in my case means putting next sheet to the tray.

BTW: I recently tested over a year old stock of Foma Excel (clone of Xtol) - worked perfectly, no deterioration observed. Stored in PET bottle, with minimum air inside.

 

[Rudeofus]

Put it this way: how bad would it be if sheets processed in consecutive order have decreasing contrast? Because that's what you will be ultimately up against, until you find out, how to compensate with extended dev time.

 

[Gerald C Koch]

Considering the amount of phenidone present 1.5 g/l and the presence of sulfite to scavenge oxygen from the solution I thought it reasonable that a second film could be developed from each 250 ml. This should be done immediately after the first one. Since there appears no information on this I thought a test would be useful.

 

[Murray Kelly]

Just to point out the quantities are 30g and 1.5g per litre not percent. In fact you'd be pushing to get 30% sulphite into solution as a sodium salt.

Rudeolfus, there was no intention of criticism intended, merely pointing it out in case someone might try after having mis-read the OP. I sincerely doubt anyone would just go ahead and do it without further reading, but one never knows!
Sorry if I hurt someone's feelings.