View Full Version : T-Max rs mixing ratios – or, “what does 1:9 REALLY mean?”

16-Mar-2011, 16:42
I keep hearing the following question in the darkroom world:

“How do I create a specific ratio of T-Max rs w/ water (for example, if I want 1:4 or 1:7 or 1:9, etc.)?”

Note 1: What I try to describe below is longer than it needs to be for most people. If you’re new to T-Max rs, I’d say keep it simple – just follow Kodak’s mixing directions, and use their recommended development times. No reason to worry too much about “ratios” until you have more experience – and some experienced users might say there’s no reason at all!
Note 2: Please keep in mind this is for T-Max rs, not T-Max “non-rs,” a different developer.

I’ve noticed that for most people, Kodak does not make this “ratio question” easy to answer. (For example, to create any ratio, do you start with the A+B concentrate, or do you start with the mixed stock? Creating, say, 1:9 the first way gives you something very, very different than creating 1:9 the second way. :confused: )

Sure, the T-Max rs packaging instructions are clear about how to mix the package’s total contents (A & B) w/ water, but nowhere do they say what final ratio this yields. And as far as I can tell, Kodak’s T-Max rs publication (http://www.kodak.com/global/en/professional/support/techPubs/j86/j86.pdf) says nothing about this ratio either (though strangely, it does define the “concentrate mix ratio” for T-Max “non-rs” on page 9, but I’ll stay on topic for now).

So I thought I’d try some quick math for myself, since Kodak doesn’t seem to trust me to theirs. ;)

I started w/ their popular boxed version of T-Max rs that makes 3.8 liters/1 gallon. I’ll stick w/ the metric system because it’s easier. The first step is to note the volumes of part A & part B:

Part A: 757 ml
Part B: 15 ml
Total: 772 ml (A+B)

Next, you’re supposed to add enough water to make 3.8 liters.

Now, it’s quite easy to add water to make 3.8 liters – anyone can do that – but exactly how much water did you just add? (We’ll need to know if we’re going to talk ratios.)

A little more math gives the answer:
3.8 liters (or, 3,800 ml) – 772 ml (A+B solution) = 3,028 ml water.

Okay, so what ratio does this create?

The exact ratio is 772ml:3,028ml (or “772ml + 3,028ml”).
More quick math reduces this to about 1:3.9 (rounded).
But let’s just say 1:4 to keep it simple. That’s the real-life answer.

(Perhaps Kodak doesn’t just tell us it’s 1:4 because everyone would howl that it’s really 1:3.922279793[…]; and maybe Kodak doesn’t say it’s this irrational number, because everyone would howl that, more practically, it’s 1:4. :p )

Be this as it may, in their T-Max rs publication, Kodak gives you time tables to develop various films w/ this solution – w/o ever identifying it as a 1:4 solution. But if you use these tables, that is the assumption. (And you’ll notice their recommended times are relatively quick for this rather strong dilution; for example, they say develop TMax-100 sheet film, in a tray, for 5.25 minutes in 72 degrees F.)

Also remember, this 1:4 solution acts as the replenisher. If you use T-Max rs as a one-shot developer, this isn’t important. But if you use the replenishing process, the 1:4 solution is your replenisher, and you’re supposed to be replenishing exhausted developer that is also 1:4.

Now, many people like the 1:9 ratio. I suspect they’ve heard “1:9” from John Sexton at this forum link (http://www.largeformatphotography.info/articles/sexton-tmax.html), and they want to “do what John does.” But how did John arrive at this 1:9 solution? He doesn’t say.

But there are two easy ways to create 1:9 (or any other ratio) if that’s what you want:

1) Bypass the “1:4” preparations above, and just go ahead and add to the A+B solution an appropriate amount of water for the amount of developer you need. For example, if you want to start w/ 1000 ml of developer, divide that amount by 10 (since 1:9 is “10 parts total”). Your result is 100 ml per part. Therefore, your A+B amount is 100ml (1 part x 100ml), and your water amount is 900ml (9 parts x 100ml). The math is somewhat different for other ratios. For example, for 1:7, you would divide by 8...

2) If you’re a “replenisher person,” chances are you already have a stock of 1:4 solution on your shelf. If you want 1:9, you would simply mix your 1:4 solution w/ an equal portion water (i.e., 1:1). In other words, you simply double its volume with water. For example, if you want 1000 ml of 1:9 in your tray, add 500 ml of the 1:4 solution + 500 ml of water. Presto, you have 1000ml of 1:9 solution. Again, the math is slightly different for other ratios.

Too much for most, but I hope all this helps put the T-Max rs “ratio question” to rest for anyone who’s been curious about the matter…


Jay DeFehr
16-Mar-2011, 17:07
1+9 = 1:10, unless you're a photographer, then 1+9 = 1:9. Simple!

Roger Cole
16-Mar-2011, 17:17
1+9 = 1:10, unless you're a photographer, then 1+9 = 1:9. Simple!

Hehehehe. Did you see my post in the other thread? ;)

Brian C. Miller
16-Mar-2011, 17:19
Jay, do you mean that if I see a chemical ratio as "1+9", that means 1:10, so 11 parts total? If something is written 1:9, then it's 10 parts total, and referred to as "1+8"?

(Or is this something to do with Roger?)

Roger Cole
16-Mar-2011, 17:24
Jay, do you mean that if I see a chemical ratio as "1+9", that means 1:10, so 11 parts total? If something is written 1:9, then it's 10 parts total, and referred to as "1+8"?

(Or is this something to do with Roger?)

I'm pretty sure he means what I meant in the other thread, that photographers have for decades now used ratios in a way that isn't consistent with how chemists use them. When a chemist sees or writes "1:9" he means a ratio of the first item to total parts - one part concentrate or chemical to nine parts total solution, which could also be written as 1+8. But when a photographer writes that what he really means is 1+9, which is one part whatever plus nine parts of water, a ratio that using a colon would properly be written as "1:10."

It's really a case where trying to clear it up adds confusion where there was none before as everyone pretty much knows that in photography the usage is now different.

So, in photography:

1:9 OR 1+9 means one part concentrate or chemical plus nine parts of water.

But in most other usage:

1:9 means one part concentrate or chemical in nine parts of total solution, so 1:9 = 1+8 (except in photography, see above!)

16-Mar-2011, 18:01
The exact ratio is 772ml:3,028ml (or “772ml + 3,028ml”).

That’s a concrete example of my photographer’s bias – they mean the same thing.

However, why X:Y = X+Y rings true to some people, and plainly false to others, deserves a dedicated thread!

1+9 = 1:10, unless you're a photographer, then 1+9 = 1:9. Simple!

Jay: Back on the main topic, are you starting from concentrate, or stock, and why did you choose one or the other if, say, 1:9 is what you want to end-up with? How would the choice make a difference in your mixing?


Jay DeFehr
16-Mar-2011, 18:02
See? Simple!

Richard M. Coda
16-Mar-2011, 18:56
AFTER you mix Part A + Part B... 100 ml concentrate with 900 ml H2O = 1000 ml.