Parameters for E-6 Process Control

[Scott J.]

I've been running Fuji-made C-41 control strips with my Kodak Flexicolor chemistry with success and would like to start monitoring the quality of my E-6 chemistry using Fuji's E-6 control strips. The info on E-6 process control is somewhat scant, but from what I've gleaned from Chapter 13 of Kodak Z-119, there are six parameters I need to measure:

1. difference in D-min (i.e., control strip RGB density values - corrected reference strip RGB density values)
2. difference in LD
3. difference in HD
4. difference in D-max
5. LD color spread
6. HD color spread.

Parameters 1-4 are pretty straight forward. What I'm confused about is how to calculate the color spread in the LD and HD patches (parameters 5 and 6, above). In C-41 process monitoring, "color spread" is a single number, which is determined by first calculating HD - LD for each of the three color channels (e.g., RHD - RLD, GHD - GLD, and BHD - BLD), then finding the density difference ("spread") between whichever two channels are the farthest apart in those three calculations. Once found, that single value is compared to the spread that was similarly calculated for the corrected reference strip, and the difference between the two determines to what degree your process is in control.

In E-6, however, it appears that color spread is defined differently and is two values instead of one (i.e., one value for the HD patch and one value for the LD patch). Here's how Kodak defines it (page 13-2):

"Color-Balance Spread Limits: A color spread is the density difference between the two most widely separated color plots of the LD and HD steps. If your process exceeds the color-balance spread limit, stop processing customer film and take corrective action. The color-balance spread limits for LD and HD are given in Table 13-1."

And here's how the Alvandi Systems E-6 Process Manual (section 2.4.8) defines it:

"An existing deviation in color balance, unlike directly measured density deviations, cannot immediately be seen from the values obtained through the measurements. The necessary values, however, can easily be calculated from the existing data. The control values obtained in the color control step (HD) and the sensitivity control step (LD) are the basis for this calculation. The difference of red minus green (R - G) and blue minus green (B - G) are obtained for both steps by mathematical calculation. Through this kind of calculation the control values for green are established to equal zero and thus become the reference point for the deviation (R - G) and (B - G)."

The author of the Alvandi document goes on to define "spread" as the value calculated from [(R - G) - (B - G)] for each of the LD and HD patches. This is sort of consistent with the Kodak definition given above, except that Kodak doesn't assume (like the Alvandi document) that the density values for the R and B channels will always be the farthest apart.

Looking back over my C-41 control strip data, it does look like the R and B channels are always the most widely separated in both the HD and LD patches, so perhaps this always holds true? In any case, if anyone has experience doing E-6 process control, I'd greatly appreciate some clarification on how the color spread is calculated. Am I essentially on the right track?

 

[John Salim]

Monitoring & plotting E-6 is actually easier than C-41.
What chemicals are you using ... three bath or a proper seven bath processing line?

You only normally need to measure RGB on four patches ( status-A filters on your densitometer ) ...
D-min ( patch 1 )
LD ( patch 3 )
HD ( patch 5 )
D-max

Enough film throughput and proper replenishment is vital.

Kodak Y-55 plotting forms are downloadable here ... https://imaging.kodakalaris.com/sites/default/files/wysiwyg/retailers/chemistry/techpub/y55.pdf

John S

 

[Scott J.]

What chemicals are you using ... three bath or a proper seven bath processing line?

I'm using six-bath Fuji-Hunt chemistry. (I'm hoping the 5-liter kits become available again soon.) I develop everything one-shot. My primary motivation for process monitoring has to do with shelf-stability of my unmixed concentrates, which can sometimes sit for months (albeit, in sealed, decanted glass bottles). My experience with Flexicolor C-41 chemistry has been that the shelf-stability of the concentrates is extremely good, but I'd like to be similarly assured that my E-6 chemicals are reliable. I shoot a lot of 4x5 and 8x10 film and the additional labor and cost is worth the peace of mind.

You only normally need to measure RGB on four patches

So, do you not normally bother calculating color spread? Both Kodak pub. Z-119 and the Alvandi Systems manual I linked to above list action and control limits for it (in addition to the four patch measurements), so I assumed it was necessary.

 

[John Salim]

Concentrate storage will be similar to C-41, the Dev's being the most sensitive of course.

No, I've never worried about calculating colour spread ( it's visually right in front of you ), but you'll always have a little to some degree.
I've never seen a plot without a little ( including from a Kodak QLab monitored lab plot ).

To some extent you've got control with a seven bath line, but as you're not replenishing, this will be limited.
If you're using Fuji Pro6 chemicals, refer to their processing manual.

( Kodak ) colour spread limits ...
( LD ) 0.08
( HD ) 0.13

and for your information....
( Kodak QLab ) colour spread limits ...
D-min plus or minus 0.02
( LD ) plus or minus 0.04
( HD ) plus or minus 0.06
D-max minus 0.10

John S

 

[Scott J.]

Thanks, John. That's helpful insight.

On the specific question about how the color spread calculations are performed, let's say I've collected the following data for the HD patch:

Here's the approach I'd tentatively take:

• Calculate the color spread in the corrected reference strip: (2.11) - (1.94) = 0.17
• Calculate the color spread in my control strip: (2.03) - (1.89) = 0.14
• Calculate the difference in color spread between my control strip and the corrected reference strip: (0.14) - (0.17) = -0.03
• Conclude that, since -0.03 is inside Fuji's published control limits of +/- 0.13 for the HD patch, my process is in control.
• Repeat the above process for the LD patch (where the control limits are +/- 0.08).

Does that look about right to you? Many thanks.

 

[John Salim]

Hi Scott, Yes they look fine but there's no reason to actually note these unless you're not plotting your readings.
Like I said, once plotted on a form, you have all the information right there in front of you.

When you start to run E-6 control strips, it's vital to factor-in the correction values from the reference strip readings as your aims.
As a visual check, you can examine your processed strip next to the reference strip on a ( good quality ) daylight balanced lightbox.

Are you processing with a machine or by hand ?

Cheers,
John S

 

[Scott J.]

Like I said, once plotted on a form, you have all the information right there in front of you.

I've built Excel spreadsheets for my C-41 process monitoring and am in the process of doing the same for E-6. The plots I've added to the spreadsheet (essentially, digital versions of Kodak's Y-55 form) are designed to show the trends in the various parameters over time and how in (or out) of the aim values, action limits, and control limits each parameter is. That's actually why I posted the question in the first place -- i.e., to ensure that I was correctly writing the spreadsheet equations for calculating color spread.

Are you processing with a machine or by hand ?

I'm using a Jobo CPE-2 with 2500-series tanks, an aquarium pump (for water circulation), and a calibrated/traceable digital thermocouple. I'm confident that the mechanical aspects of my process are good and simply want to be able to validate the quality of my E-6 concentrates over time. With the disappearance of the 5-liter Fuji-Hunt E-6 kits, I've been contemplating taking the plunge on the lab-sized Fuji Pro6 chemicals, but as they come in much larger quantities, I'd want to have a way of confirming that the concentrates are still in good shape before committing any film to them. I'm also tempted to try a three-bath kit (Tetenal, etc.) and see how in-control those kits can be if used one-shot. It seems the main concern over the three-bath process has to do with the efficacy of the blix (i.e., retained silver). Running control strips should be a good way of quantifying to what degree that's a valid concern.