More motes on Rodinal & the FDC
Reading the Film Developing Cookbook it's apparent that there are misconceptions about the "Rodinal Type" developer listed and Agfa Rodinal of all vintages over the years.
1. First the date is given as 1881 but Andresen didn't discover p-Aminophenol until 1888, Rodinal came on the market in 1891.
2. Rodinal has always been a p-Aminophenol developer using the free base, although in the early years the hydrochloride was used to prepare the free base.
3. Rodinal (except Agfa after 1964) has always used Potassium Sulphite and just enough Hydroxide to form p-Aminophenolate, and no excess. The level of Hydroxide was increased by Agfa in their 1964 re-formulation, not decreased.
The FDC states that "Agfa Rodinal still contains p-Aminophenol and Potassium Hyrdroxide but in much smaller amounts". The Major change in 1964 was an increase in the Hydroxide taking the concentrate pH from 11.8 to 14, at the same time the amount of developing agent was cut by approx 20%. The FDC makes no reference to the continued production of the older formula by Orwo/Calbe so no comparison.
It's easy to see where this misunderstanding comes from. As Agfa themselves stated around the beginning of last century "In addition to neutral sulphite and water "Agfa"-Rodinal contains only an alkaline salt of Paramidophenol, but no excess of caustic alkali".
The older formula (in the FDC and in the first post in this thread) uses 100 g of p-Aminophenol and 300gms of Potassium Metabisulphite, and about 216ml of a 400ml 50% Sodium Hydroxide solution (107.95 g) to form a 50/50 mix of Sodium and Potassium Sulphite (170.1 g + 213.5g). A small additional amount of Sodium Hydroxide is used to convert the p-Aminophenol free base, and slightly more for the Hydrochloride.
Agfa stopped using Metabisulphite as the source of the Sulphite sometime before WWII and began using Potassium Sulphite instead, probably for economic reasons, the direct replacement in the FDC formula would be 427.11g, the amount of Hydroxide needed would fall to around 50g, a bit more if you use p-Aminophenol Hydrochloride rather than the free base.
It's the amount of Hydroxide in the final developer that's important, rather than any used to convert Metabisulphite to Sulphite which completely disappears in the process anyway.
One molecule of Potassium Metabisulphite and two Potassium Hydroxide react to give two Potassium Sulphite and water
4. Bromide and anti-foggant. In the FDC Page 59 (Agfa Rodinal - 1964 onwards) Bill Troop states that "Potassium Bromide has also been added, which would not be necessary if p-Aminophenol was the sole developing agent"
However we know that Agfa were already using Potassium Bromide and another anti-foggant (P.1347) many years earlier in Rodinal from F.I.A.T. and British RAF reports, they were probably introduced during the 1930's, so the statement doesn't make sense. The amount of Bromide then works out at less than 1% (0.77%) so would not be shown on Calbe's MSDS if they use a similar level.
There are unsubstantiated reports that that the formulae Andresen himself published can sometimes cause Dichroic fog, whether this is due to the use of the Hydrochloride or incorrect balancing of the alkali by adding excess we can't know.
But an increase in the alkalinity particularly as it's a hydroxide will greatly increase the potential for fog even more so because there's such a low level of sulphite and we know that dilute Agfa Rodinal has a higher pH than even the Calbe R09 concentrate, before that drops itself with dilution.
5. If Agfa Rodinal is added to Bill Troop's table of High Acutance developers on page 59 of the FDC then a 1 in 50 working solution would fit extremely nicely alongside Beutler etc
P-Aminophenol 0.82 g
Potassium Sulphite 6.8g
Potassium Hydroxide 0.12
There's about 6 g per litre free Potassium Hydroxide in Agfa Rodinal concentrate and the p-Aminophenolate is also alkali so the pH is somewhere around 11.55 even when diluted 1+50, (Agfa's own pH figure).
In comparison Calbe R09 needs to be used at 1 in 40 to achieve roughly comparable results and in this case we would have:
p-Aminophenol 1.25 g
Potassium Sulphite 6 g
Relying on the alkalinity of the phenolate itself the pH will be much lower than Agfa Rodinal which is why over 50% more developing agent is needed.
6. We do know the precise amount of p-Aminophenol in Rodinal, it's in the MSDS along with the Hydroxide, 4.1% and 2.7%, also all Rodinal MSDS's etc confirm it's the free base, typical German precision.
Although Agfa Rodinal has nearly 20% less developing agent than Calbe R09 (old Rodinal formula) it's working at a much higher pH
So these facts rule out Bill Troop's speculation in the FDC & on the Internet that a second developing agent has been added. p-Aminophenol shows good additivity & super-additivity with other developing agents so add even a trace at Agfa Rodinal's high pH's and the increase in activity would take Rodinal into a completely new realm hitherto unexplored
which more than compensates.
The FDC Rodinal type dev will work better with 133.4 g of p-Aminophenol Hydrochloride per litre, and made up to a litre will be more similar to R09 but with a lower sulphite content and no anti foggants. Of course it works as is it's such a simple develop.
Ian
