Home-mixed D76 lacking strength

So, I've been having this issue several times in a row when mixing D76. The stock solution has 1/2 the developing strength of the store-bought developer, i.e. I need to develop for twice as long to get the same development as before.
What am I missing? I use photo grade hydroquinone, metol, and borax. My only suspicion thus far refers to my sulfite - previously I had used a pure-for-analysis Na2SO3, but switched to "pure" recently. However, I cannot recall precisely if my first failing batches of D76 were mixed with it.
On the package of the sulfite, it it stated that it contains min. 94% Na2SO3, iron: max. 0.005%, heavy metals max: 0.001%. This seems to be fit for photo use, at least according to a book I have.
So, any ideas in what is going wrong? I can't seem to think of any reason why the developer won't work. Other developers I have mixed with the same sulphite, like ID-68, work exactly as they should.

Yellow packets are mixed with Kodalk, not borax, thus the slight difference in activity. The easiest thing to do is to calibrate your process to your homemade recipe, and be happy with it. This is what I am doing and I am very happy with the results.

If you're making up ID-68 with the same chemicals except for the Metol/Phenidone then possibly your Metol is suspect. If the Sulphite is reduced in level you should get increased rather than decreased activity. What form of Sulphite are you using ideally it should be anhydrous which is the commonest form found in Europe.

Ian

Yes, the sulfite is anhydrous, a somewhat dense, fine powder, with a very slight off-white hue. I don't know whether to suspect Metol, as I also got reduced activity when mixing E76, which uses Vit C and phenidone.
The thing is, I'm mixing these developers for our student darkroom, and other students are reporting the lack of sensitivity. Since, I haven't used my latest batches, I can't say if I'm at fault, or it is their processing. However, I ruled out the sulphite several minutes ago by mixing batches with my old Na2SO3 and the new "suspect" one. They show no difference in activity when a paper test strip was developed at exactly the same conditions.

I know no one will listen to such an idiot like I am, but trust me I know the issue, it is because you are substituting kodalk with borax. Mix two, yours and proprietary, and measure pH, you will see the difference.

Michael you're right Kodak don't use Metaborate (Kodalk) in D76, instead they use a buffered borax form of D76 somewhere wbetween the plain borax original D76 formula and D76d which uses 8g Borax and 8g Boric acic.

So I'd agree it has nothing what so ever to do with needing to use Metaborate.

Ian

Are you dissolving a 'pinch' of sulfite up front before starting to dissolve the metol?

If not, the metol may be oxidized by dissoved gasses (namely oxygen) in the water before the rest of the sulphite is added after the HQ.

If the metol is partially degraded, then there is less of it left active to be superadditive with the HQ.

This small mixing technique could explain the difference in activity you are seeing.

Hm, Mike, you may be on to something. What I do is prepare two dry parts, one containing the developing agents with some sulfite(10g), and another with the borax and the rest of the sulfite. Maybe that is making a difference.
Thank you all for the quick responses; I may prepare a variant of D76 - maybe D76H, to test the Metol out, and a PQ one to see how that compares.

My formula says 2.0 g/l Borax. It calls for 100 g/l Sodium Sulfite anhydrous. If you use the hydrate of the Sulite, then there is not enough present.

If you are able, compare the pH values of Kodak D76 and your home brew. If the pH is low in your home brew, then it is one of the above 2 problems. Hydrated Sulfite or not enough Borax.

PE

Both Ilford and Kodak increased the buffering of ID-11/D76 in their commercial products from the published formulae, Ilford proably just incresed the Borax level (they have a variant with 3g/l Borax) but it's not known how much Kodak incresed it other than adding a small amout of Boric acid, this was probably done because far more people now use the developer diluted 1+1 to 1+3, it was of course designed to be used full strenght but it also gives greater stability when replenished.

So you could increse the Borax to 3g/litre with no ill effects. As I said previously decreasing the Sulphite to 70 or 80g/litre increases the developers activity and you get slightly better film speed and shadow detail, also better sharpness. This was the approach taken by Agfa (& Agfa ansco), adox (when still German and then under Dupont) etc and also Ilford in ID-68 (Microphen).

Ian

Nikola Dulgiarov said:

Hm, Mike, you may be on to something. What I do is prepare two dry parts, one containing the developing agents with some sulfite(10g), and another with the borax and the rest of the sulfite. Maybe that is making a difference.
Thank you all for the quick responses; I may prepare a variant of D76 - maybe D76H, to test the Metol out, and a PQ one to see how that compares.

Click to expand...

I think that the method you are using to compund the developer may be part of the problem. The ingredients should be dissolved separately in the following order;

Water 125F 52C 750ml
A pinch of Sodium Sulfite
Metol 2gm minus the above mentioned pinch
Sodium Sulfite Anhydrous 100gm
Hydroquinone 5gm
Borax 2gm
Water to make 1000ml

If I remember correctly Metol is not very soluble in a concentrated solution of Sodium Sulfite and needs to be dissolved first. The pinch of Sulfite added to the water is to help prevent oxidation of the Metol until the rest of the sulfite is added.

Zathras said:

I think that the method you are using to compund the developer may be part of the problem. The ingredients should be dissolved separately in the following order;

Water 125F 52C 750ml
A pinch of Sodium Sulfite
Metol 2gm minus the above mentioned pinch
Sodium Sulfite Anhydrous 100gm
Hydroquinone 5gm
Borax 2gm
Water to make 1000ml

If I remember correctly Metol is not very soluble in a concentrated solution of Sodium Sulfite and needs to be dissolved first. The pinch of Sulfite added to the water is to help prevent oxidation of the Metol until the rest of the sulfite is added.

Click to expand...

Whoops, I made a booboo. The formula should have read;

Water 125F 52C 750ml
A pinch of Sodium Sulfite
Metol 2gm
Sodium Sulfite Anhydrous 100gm minus the above mentioned pinch
Hydroquinone 5gm
Borax 2gm
Water to make 1000ml

vyshemirsky said:

I know no one will listen to such an idiot like I am, but trust me I know the issue, it is because you are substituting kodalk with borax. Mix two, yours and proprietary, and measure pH, you will see the difference.

Click to expand...

I use the old Zone 5 substitute formula for D-76 which I believe uses Borax, and get great results every time. I could dig the formula out if helpful.

And by the way, the metol I use I bought back in 1987!!

vyshemirsky said:

Yellow packets are mixed with Kodalk, not borax, thus the slight difference in activity. The easiest thing to do is to calibrate your process to your homemade recipe, and be happy with it. This is what I am doing and I am very happy with the results.

Click to expand...

MSDS for D-76 quotes sodium tetraborate, pentahydrate which is borax but not in the usual decahydrate form.