Confused re: D-76 Max Capacity and Min Requirement

[rcam72]

I'm not a chemist or a darkroom chef, so the following has confused me somewhat:

D-76 capacity = 4 rolls per liter of stock
D-76 min required stock = about 120ml per roll
4 rolls require 480ml stock which exceeds the capacity for 1 liter by about 2x.

Why the discrepancy?

I've never thought about it until now. I've looked at the other threads on this and that is one of the reasons I'm confused.

 

[brucemuir]

Because you can dilute the D76 stock solution 1:1 and further to get finer grain
the 120ml is min if you dilute

Where are you getting these numbers?
from a Tech Pub?

 

[Kevin Kehler]

I get more than 4 rolls per liter of stock - I just did 6 rolls of 120 in a liter of stock (with a liter of water, so 1:1 dilution) which came out fine (as it usually does).

 

[polyglot]

Are you reading J78? The capacity really is 4 rolls per litre of stock, even if you dilute. If you want to use less than that, you must extend the development time. From the datasheet, end of page 2:

You can develop one 135-36 roll (80 square inches) in 473 mL (16 ounces) or two rolls together in 946 mL (one quart) of diluted developer. If you process one 135-36 roll in a 237 mL (8-ounce) tank or two 135-36 rolls in a 473 mL (16-ounce) tank, increase the development time by 10 percent (see the following tables).

In other words, if you use only 120mL of stock per film, the developer will be slower-acting (starting to exhaust) and therefore you must extend development time in that case.

 

[rcam72]

Where are you getting these numbers?
from a Tech Pub?

The numbers are from the Kodak pub for D-76, J-78. It lists 237ml (8oz) minimum for a 1:1 dilution. The 120ml comes from taking half of that as the minimum for stock solution.

Thanks Polyglot. I thought that time had something to do with it but I wasn't sure. So 250ml stock solution per roll (80 sq in) is the minimum without adjusting the development time, going by the Kodak book.

I was sitting fat, dumb, and happy until I checked a similar thread on the subject a couple of days ago and had this crisis of confidence.

 

[polyglot]

Note that the required extension is only 10%. So if you fail to extend the time, you're talking maybe a third of a stop difference and who knows, maybe your thermometer reads a bit cold and you had plenty of development. You'll find no shortage of people (e.g. KK above) who are happy using unadjusted times with very small quantities of developer even if that's not The Official Kodak Instruction. Probably doesn't matter unless you have a particularly dense/high-key roll.

 

[rcam72]

You'll find no shortage of people (e.g. KK above) who are happy using unadjusted times with very small quantities of developer even if that's not The Official Kodak Instruction.

That was me until I got curious.

 

[Ronald Moravec]

120 ml stock + 120 ml water has worked for 36 exposure films for me for 30 years now.

If you have a roll of snow scenes, you might try 240+240 for grins. I never do. Print time same as anything else so it must work.

J78 has a big safety margin built in.