The Change to an RH Designs Process Master

The Process Master (PM) helps keep your film processing consistent by normalizing your process temperature and managing the agitation cycles.

Process compensation is based on two components, a temperature sensor, and your known baseline processing time.  The baseline processing time is simply your N development time at 68F (20C).  The PM operates in real time at 20C.  The temperature sensor monitors the tank temperature and makes adjustments (about 8% per degree C ) to the development time.  If your process temperature is 25C then the total processing time will be 40% shorter relative to your base time at 20C.  In other words the process master compensates the development process by increasing the countdown.time.  Agitation time is also compensated.

The control of agitation is accomplished via single beep at 30 seconds or a double beep at 60 seconds.  If your processing film at 25C (77F) the agitation indicator will beep but the clock is running faster than normal to compensate for the higher processing temperature, so actual agitation time is reduced.  Therefore 60 seconds of initial agitation at 25C is forshortened by 24 seconds, and cyclic agitation of 10 seconds is forshortened by 4 seconds. 

This issue presented itself while working with the PM when it became obvious that my normal film processing procedure was significantly different from the PM routine.  This naturally brought up some questions about the two processes.  I was curious to understand better the possible advantages or disadvantages of using the PM and my routine film developing process.

My development process consisted of the following routine: 1) using 2 reel stainless steel tank and reels, 2) filling the tank first then starting the time, 3) agitation for one full minute, 4) stand one full minute, 5) agitation of 3 inversions in 10 seconds, 6) stand one full minute, 7) repeat until total process time reached.

When I process according to my routine proceedure, initial agitation, stand time, and cyclic agitation are constants and the only variable is the total process time due to different process temperature.  Traditionally temperatures should be consistent and standardized at 20C or 22C.  Unfortunately my darkroom temperature fluctuates seasonally so heating or cooling chemicals so process temperature is always the same can be difficult when you are only using working solutions.  Concentrated solutions of developer and fix overcome this problem because you mixing working solutions as needed at the standardized temperature.  This is the better proceedure overall.

Compared to using the PM, the following differences were apparent:

1)  Initial agitation will be foreshortened by about 8% per degree above 20C, (Step 3). 2)  The stand time is also foreshortened, (Step 4).  3)  Clyclic agitation time is also foreshortened, (Step5).

The differences in processes are significant.  To illustrate this I converted the development process into the unit agitation seconds, which means the number of seconds of actual agitation in real time for both processes at two temperatures, 20C and 25C, and two times, 10 minutes and 30 minutes. 

I used the following routines to calculate total agitation time, and total stand time for each process summarized in Table 1, 2, and 3.

Process Master 10 minutes:

Temp = 20C.  60 sec initial agitation, 60 seconds stand, 10 seconds agitation, 50 seconds stand.  Total process time 600 seconds.

Temp = 25C.  36 sec initial agitation, 36 seconds rest, 6 seconds agitation, 30 seconds rest.  Total process time 395 seconds.

My routine process 10 minutes:

Temp = 20C.  60 seconds initial agitation, 60 seconds rest, 10 seconds agitation 60 seconds rest.  Total process time 600 seconds.

Temp = 25C.  60 sec initial agitation, 60 seconds rest, 10 seconds agitation, 60 seconds rest.  Total process time 395 seconds.

Process Master 30 minute

Temp = 20C.  60 sec initial agitation, 60 seconds stand, 10 seconds agitation, 50 seconds stand. Total process time 1800 seconds.

Temp = 25C.  36 sec initial agitation, 36 seconds rest, 6 seconds agitation, 30 seconds rest. Total process time 1186 seconds.

My routine process 30 minutes:

Temp = 20C.  60 sec initial agitation, 60 seconds stand, 10 seconds agitation, 50 seconds stand. Total process time 1800 seconds.

Temp = 25C.  36 sec initial agitation, 36 seconds rest, 6 seconds agitation, 30 seconds rest. Total process time 1186 seconds.

Table 1 - Total agitation time of Process Master routine vs. my routine for 10 minute process time.

Table 2 -Total agitation time of Process Master routine vs. my routine for 30 minute process time.

Table 3 - Ratio of agitation to stand time

Data:

Table 1 shows my original process and the PM routine for a 10 minute development time at 20C and 25C.  The difference between the processes is minimal, 10% more agitation seconds for the PM routine compared to my original routine at 20C temperatures and 9% difference at 25C.  At 20C each process routine yields significantly less agitation then at higher temperatures, 24% for both the PM routine and my original routine.  Table 2 extends the two routines from a 10 minute process to a 30 minute process.  At 30 minutes there is a 12% increase in agitation time at 20C for the PM routine and only a 3% increase at 25C.  Across temperatures the PM routine yields a 35% reduction in agitation time while my original routine yields a 23% reduction in agitation time.  Table 3 indicates the ratio of stand time to total agitation time for each process at 20C and 25C for a 10 minute and a 30 minute processing routine.  The PM routine shows consistency across temperature which is to be expected but is not consistent across time reflecting the reduction in total agitation and increase in stand time.  My process shows no consistence across time or temperature.

Discussion:

The data indicates that agitation that my original process lacks consistency across time and temperature.  At longer process times, for example my routine for TriX in FX2 calls for a 30 minute process.  At 30 minutes agitation is significantly reduced and stand time significantly increased.  At higher temperature of 25C agitation time is increased compared to a process at 20C.  The expected result would be underdeveloped negatives when using longer process times and over developed negatives when using increased temperatures.  I have actually observed this and now I know why it is the case.

The PM routine corrects for the inconsistency across temperature.  The agitation time to stand time ratio is the same (1:3 and 1:4) for both 20C and 25C respectively.  However, at longer processing times and higher temperatures agitation is decreased and stand time increased.  

The first problem to address is dealing with what I would call the film processing constants: initial agitation and cycle agitation.  Simply, film needs at least 60 seconds initial agitation and at least 10 seconds cyclical agitation  thereafter.  Anything less risks inconsistent development.  Given that these are the constants the variables then are: the stand time between agitations and temperature.

When working with the process master the base-line temperature is 20C and there we start with a 60 second initial agitation and a 10 second agitation cycle.  If we are agitating every minute the stand time becomes 50 seconds per minute.  If we then process at a higher temperature the Process Master routine will reduce development time accordingly (8%/degree C).  Also, the initial and the cyclic agitation reminder beeps are also reduced.  When the process temperature reaches 25C both initial agitation and cyclic agitation are reduced to a point I would consider problematic for film development.  In this model it is significantly reduced to 36 seconds and 6 seconds per minute respectively.  I believe this to be too short a time for proper agitation especially if your developing 2 rolls in a small stainless steel tank. 

The easiest way to solve this problem is to separate the beep function from the compensation function so the agitation reminders can be programmed in real time.  There would have to be an initial agitation program, a begin cycle agitation beep and an end cycle beep.  Another solution is to not worry too much about the minor corrections and apply only what may be considered a significant correction.  To determine what the significant correction are likely to be we should go back to the original assumptions and dig into their background.

Assumption 1 - initial agitation:  Anchell and Troop's recommend the following: 60 seconds initial agitation unless the entire film surface can be submerged in developer in less then 5 seconds.  It would seem that our assumption is in line with this source.  I can fill my tank in 10 seconds, but I don't start the time until the tank is full.  Anchell and Troop do not mention this so I'll assume they have the time going while pouring since Anchell uses a wide mouth Paterson Super System 4 tank and reels.  In my case at 25C I would be getting a full 30 seconds of initial agitation.  Is this enough?  Could using a presoak prior to pouring the developer mitigate this issue?  I have evidence that 30 seconds at 25C is not enough time as a curious thing happened when using the PM system:  I agitated some rolls for 30 seconds and 60 seconds then 10 seconds every two minutes at 25C.  The 30 second rolls clearly measured less CI.

Assumption 2 - cyclic agitation:  Anchell and Troop recommend 10 seconds agitation per minute unless your total development time is less then 5 minutes.  They say that 5 minute agitation cycles do not allow enough time "to get any movement or flow breakup going."  I also have evidence of this as I reduce agitation routinely to achieve lower contrast with Metol based solvent formulas, but, have experienced very uneven development with non-solvent formulas.  This is very pronounced when developing 120 film.  Rolls developed at 25C agitated for 5 seconds per minute showed less CI then those agitated for 10 seconds every two minutes, the opposite of what was expected.  If I had to speculate from the tests, crude as they were, I would say the initial development was more instrumental in effecting the overall contrast and the agitation cycles the evenness of the development.  I would add that I have not had this issue present itself when using solvent-based developers.

Holding these assumptions across the process creates another issue regarding stand time between agitation.  My impression is that stand time is as important as the other components of processing.  Decreasing stand time can affect development especially when using high definition non-solvent developers which rely on very dilute formulas to create areas of local exhaustion on the film surface.  Foreshortening the stand time then defeats the purpose of these formulas.  I have seen evidence of this when working with FX2, Pyrocat, PMK, and DiXactol as increasing total agitation and decreasing total stand time significantly reduces internal definition of the negative image.

Table 3 indicates that for normal processing a ratio of agitation to stand time for a particular process should be 1:3, or 3x more stand time then agitation time or 1:4 depending on the process method.  The point is to create consistency across variations in the process.  The reference for this as the standard is empirically derived from the recommended process routine of 60 initial agitation and 10 seconds agitation per minute.   As mentioned before the process master is consistent in this regard showing the same ratio across the temperature range.  This is an improvement over my process which shows increasing stand time at 20C, 30 minutes which is something I have previously noticed.  What is also apparent is that at longer processing times this ratio changes to 1:4 or 4x more stand time then agitation time suggesting more agitation may be called for.

Plausible corrections:

Correction 1:  At longer development times the ratio between total stand time and total agitation time should be the same compared with shorter development times.  Is this assumption correct? Should this be changed?  I do not believe it is practical to worry about this because most processing times do not extend out past 15 minutes.  This may be a factor in semi-stand development where times do extend out that far.

Correction 2:  At higher temperatures there is the issue of foreshortened agitation time due to the PM agitation reminder beeps not working in real time.  Rather of a full 60 second initial agitation we get 30 seconds.  Rather then a full 10 seconds cyclic agitation we get 6.  Can this be corrected?  Table 3 shows that my original processing routine maintains the minimum initial and cyclic agitation times and keeps the the agitation time to stand time ratio consistent.

Conclusion

Initial agitation and subsequent cycle agitation should remain constant across process temperatures; one minute initial agitation and 10 seconds subsequent agitation.  When processing at higher temperatures using the process master (about T>24C) agitation constants are significantly reduced resulting in less and uneven development.  The initial agitation seems to be correlated more with less and uneven development then shortening subsequent cyclic agitation.  Correction at higher temperatures should be considered for both initial agitation and cyclic agitation.  However, doing this will decrease the agitation to stand-time ratio.  For example correcting for approximate real-time by doubling initial stand time and cyclic agitation time results in a ratio of 1:2.4.  By decreasing total agitation seconds  by increasing stand time from 72 seconds to 120 seconds on the process master keeping the 12 seconds for cyclic agitation  the ratio is restored to 1:3.  In practice this has yielded the best results at higher temperatures.

When using the Process master at temperatures greater then 24C initial agitation and cyclic agitation should be compensated to reach the following parameters:

1.  At least 60 seconds (real-time) initial agitation.

2.  At least 10 seconds (real-time) cyclic agitation.

3.  Agitation to stand-time ratio between 1:3 and 1:4

Example 1-  Extended Stand and Agitation Time- 10 minute process time at 20C when temperature is 25C

90 seconds initial agitation.

120 seconds stand

20 seconds cyclic agitation

120 seconds stand

20 seconds cyclic agitation

120 seconds stand

20 seconds cyclic agitation

90 seconds stand

END PROCESS - 600 seconds total process time. RATIO 1:3

Example 2 - Extended Stand Time -10 minute process time at 20C when temperature is 25C

84 seconds initial agitation.

120 seconds stand

14 seconds cyclic agitation

120 seconds stand

14 seconds cyclic agitation

120 seconds stand

14 seconds cyclic agitation

120 seconds stand

14 seconds cyclic agitation

64 seconds stand

END PROCESS - 600 seconds total process time.  RATIO 1:4

 Example 3 - No extension of stand or agitation -10 minute process time at 20C when temperature is 25C

84 seconds initial agitation.

84 seconds stand

14 seconds cyclic agitation

84 seconds stand

14 seconds cyclic agitation

84 seconds stand

14 seconds cyclic agitation

84 seconds stand

14 seconds cyclic agitation

84 seconds stand

14 seconds cyclic agitation

26 seconds stand

END PROCESS - 600 seconds total process time.  RATIO 1:3

These examples in theory work well but in practice this is difficult to achieve with a digital timer counting down from your process time.  After two years of using the process master this is how I've ended-up developing at elevated temperatures:

T- 12 minutes (TriX in D23 at 73C, 74C, or 75C.  (My room fluctuates between 70C and 75C))

12 to 10:30 minutes initial agitation (90 seconds)

10:30 to 9 minutes stand (90 seconds)

9 to 8:40 minutes agitation (20 seconds)

8:40 to 7 minutes stand (100 seconds)

7 to 6:40 minutes agitation (20)

6:40 to 5 minutes stand (100 seconds)

5 to 4:40 minutes agitation (20 seconds)

4:40 to 3 minutes stand (100 seconds)

3 to 2:40 agitation (20 seconds)

2:40 to 1 minute stand (100 seconds)

1 to 40 seconds agitation (20 seconds)

40 seconds to 0 stand (40 seconds)

Total agitation seconds = 190

Total stand seconds = 530

RATIO =  1:2.8

I shorten the initial stand time to 90 seconds in order to get back in sync with the BEEP.