A question about mixing chemistry I should know the answer to, but dont

[weasel]

About a year and half ago I went back to mixing d76H after having trouble getting xtol. I tend to shoot irregularly, so prefer to not a mix a bunch of chemistry that goes bad before I can use it, so usually mix it in one liter batches.
Here is my question; is there any reason I can't, or shouldn't, pre mix the dry chemicals and store ready to mix with water?

 

[Alan9940]

About a year and half ago I went back to mixing d76H after having trouble getting xtol. I tend to shoot irregularly, so prefer to not a mix a bunch of chemistry that goes bad before I can use it, so usually mix it in one liter batches.
Here is my question; is there any reason I can't, or shouldn't, pre mix the dry chemicals and store ready to mix with water?

Depending on the chemicals involved in the formula, some chemicals won't dissolve properly unless the prior one has completely dissolved. I generally mix in the order given and make sure the chemical has gone into solution before adding the next. My only exception to that is 510-Pyro. I toss the few chemicals involved into the TEA and turn on my hot plate mixer. Don't know the exact formula for D76H, but since Kodak packaged everything together for D76 you'd probably be okay.

 

[koraks]

is there any reason I can't, or shouldn't, pre mix the dry chemicals and store ready to mix with water?

As long as you're going to dissolve all of it in one go, no, I don't think it should be much of a problem with D76h. Note what @Alan9940 says about order of mixing for other developers than D76 et al.
I wouldn't try to portion it up after mixing the dry stuff and before mixing with water to make your stock. It's kind of hard/impossible to make a truly homogeneous mix out of dry powders at home.

Be sure to store the dry powders in such a way that moisture can't get to it, because that stuff is going to cake like mad if it gets damp, I bet.

 

[Paul Howell]

I agree, Kodak D76 is sold as a single mix, I don't see any reason why you can pre mix your dry chemistry and just add water. But your stored mix needs to be kept dry, if you happen to have a vacuum food saver pump and bags, that will work.

 

[Vaughn]

From what others have posted, packaged developers contain addition ingredients to help with mixing and to allow for a range of water quality to be used. So I would not expect stored home-mixed chemicals to mix exactly like packaged developer might...but it may not be a significant difference.

 

[snusmumriken]

I agree, Kodak D76 is sold as a single mix, I don't see any reason why you can pre mix your dry chemistry and just add water. But your stored mix needs to be kept dry, if you happen to have a vacuum food saver pump and bags, that will work.

Wouldn't it suck all the powder out of the bag?

 

[Sirius Glass]

I fix your chemicals are packaged, keep them packaged until you mix them.
If you mix your chemicals, how will you keep them dry and unexposed to anything that will break them down? I would recommend you keep each of the reagents separately and mix when you are ready to use them.

 

[grat]

Wouldn't it suck all the powder out of the bag?

Anecdotally, the one time I tried vacuum sealing D76, there was no problem. I was using a fairly powerful food-grade vacuum sealer with the textured bags, and the D76 particulate isn't that fine.

 

[albada]

Some comments:

1. Some developers can degrade when exposed to alkali (sulfite and borax, in this case). So it's best to keep them separate. Kodak adds ingredients to prevent this from being a problem, so they can put D76 powders in one bag.
2. Metol dissolves more slowly in a high-sulfite solution, so you should add it first (and thus separately).
3. Water contains oxygen, which can harm the metol, so formulas for metal-based developers like D-76 often tell you to first add a "pinch of sulfite" to scavenge the oxygen, then the metol, then the rest of the sulfite.

For the record, the formula for D-76H is the same as D-76, but with the hydroquinone omitted and the metol boosted to 2.5 g. Grant Haist created this formula, hence the "H" in its name.

Mark Overton

 

[weasel]

The metol reacting with the alkali seems the best answer yet, thank you.

 

[cmacd123]

Kodak has been known to use tricks like coating one chemicaal with another. (think of Jelly Beans - or M&Ms) so that the disolve in the right order. That and also using different ingredients that the Published formula. (more - different - or extra) to get the same results. Many have noted that scratch Mix D-76 changes activity over the first few days after it is mixed.
Note that Ilford ID 11, which has a published formula indistingwishable from D76 is shipped as a two part package.

 

[Paul Howell]

Some comments:

1. Some developers can degrade when exposed to alkali (sulfite and borax, in this case). So it's best to keep them separate. Kodak adds ingredients to prevent this from being a problem, so they can put D76 powders in one bag.
2. Metol dissolves more slowly in a high-sulfite solution, so you should add it first (and thus separately).
3. Water contains oxygen, which can harm the metol, so formulas for metal-based developers like D-76 often tell you to first add a "pinch of sulfite" to scavenge the oxygen, then the metol, then the rest of the sulfite.

For the record, the formula for D-76H is the same as D-76, but with the hydroquinone omitted and the metol boosted to 2.5 g. Grant Haist created this formula, hence the "H" in its name.

Mark Overton

I think Mark is right, ILford ID 11 and Ansco/GAF 17 is not or in the case of Ansco 17 was not sold as a single mix.

 

[albada]

Kodak has been known to use tricks like coating one chemicaal with another. (think of Jelly Beans - or M&Ms) so that the disolve in the right order. That and also using different ingredients that the Published formula. (more - different - or extra) to get the same results. Many have noted that scratch Mix D-76 changes activity over the first few days after it is mixed.
Note that Ilford ID 11, which has a published formula indistingwishable from D76 is shipped as a two part package.

I like the analogy of M&Ms. We home brewers cannot perform such tricks that Kodak is capable of.

The pH of D-76 rises over time (I don't know why), which raises its activity, and which motivated Grant Haist to alter the formula, resulting in D-76H. Here's the complete formula. Note that there are two variations of this formula: one with 2.5 g of Metol and the other with 2.5 g of borax. The rule is that one must be 2.5 g and the other must be 2 g. You might wish to use 2.5 g of whichever chemical is cheaper. Follow the steps in this order. (scroll down if there's white space below)

Water at 125F/52C	750 ml
Sodium sulfite anh.	only a "pinch" (to scavenge oxygen)
Metol	2.5 g (or 2 g if borax is 2.5 g)
Sodium sulfite anh.	100 g
Borax decahydrate	2.0 g (or 2.5 g if metol is 2 g)
Cold water	to make 1 liter

I got these two variations of this formula from The Film Developing Cookbook (2nd ed.), pages 52-53. I recommend this book for anyone interested in mixing his own developers. This passage also discusses the rising-pH problem, and various proposed solutions for it. The book concludes the discussion about D-76 by saying, "This variation, which we designate D-76H, is strongly recommended to all users of D-76 who mix their own."

Mark Overton

 

[Raghu Kuvempunagar]

is there any reason I can't, or shouldn't, pre mix the dry chemicals and store ready to mix with water?

Why do you want to premix the three dry components of D76H? Not sure what you'll gain by doing so versus keeping them separately stored and used as per your needs.

 

[weasel]

Why do you want to premix the three dry components of D76H? Not sure what you'll gain by doing so versus keeping them separately stored and used as per your needs.

Just for convenience. Setting the scales up, getting the chemicals out, etc, is a task that adds time to develop film. It would be easier, since I have to get that stuff all together and set up anyway, to do a number of batches at once, that I only have to mix in water to use.

 

[Bob AZ]

I make up 5 or 6 batches at a time of the separate dry chems in small, colored and labeled plastic ziplock snack bags stored in a cool dark cabinet. The measuring process is somewhat slow and meticulous, and I find it is as easy to make of 6 batches as one because I use my firearm reloading balance scale which has to be set for each different weight. Another tip: get a basic magnetic stirrer, I paid about $30 and it really helps.

 

[Doremus Scudder]

A couple of observations:

First, I would be hesitant to use film developer mixed from dry chemicals right away. Minuscule undissolved particulates often remain and can stick to the film causing spots and areas of higher density. Even filtration will often not remove the smallest of these. Best practice is to mix your developer from the dry mix and then let it sit for a few hours.

If you want the convenience of mixing small amounts of developer for one-shot use, then get one of the liquid concentrates. HC-110 (and the clones from other manufacturers) was formulated to give similar results to D-76, it that's the look you're trying to get. There are many others: Rodinal, PMK, Pyrocat, etc.

If you have dry chemicals around and you're mixing from scratch, then make up a concentrated stock solution that you can dilute to working strength when you need it. Stock solutions keep for months.

Best,

Doremus

 

[albada]

I make up 5 or 6 batches at a time of the separate dry chems in small, colored and labeled plastic ziplock snack bags stored in a cool dark cabinet. The measuring process is somewhat slow and meticulous, and I find it is as easy to make of 6 batches as one because I use my firearm reloading balance scale which has to be set for each different weight. Another tip: get a basic magnetic stirrer, I paid about $30 and it really helps.

To keep the alkalis from harming the metol, you should fill two bags per batch: bag A with metol, and bag B with sulfite+borax. To mix, add a pinch from B, then add A, then add B. Or skip all this hassle and use HC-110 as Doremus suggested.