Chromium intensification failure. Why?

[bernard_L]

Yesterday first experiment with chromium intensification. Test exposures Neopan-400 135, Kodak reflection scale. Developed 9'30" in D76 1+1. Fixed, washed, dried.

Chromium intensifier Ilford IN-3 as documented by, e.g. Ian Grant. Stock solution potassium bichromate 10% (25g in 250cc). To avoid repeated handling of concentrated HCl, I prepared Stock HCl diluted 1/10 from the concentrated HCl. Bleaching solution 20cc stock potassium bichromate; 5cc stock HCl; water to make 200cc. So HCl final concentration is is 0.25% (relative to "concentrated" HCl), jus as if I had mixed 2.5cc conc. HCl into 1000cc water, as per the official recipe.

Immerse film strip in bleach, in tray, under normal room artificial lighting; intermittent agitation. Image fades in ~3min; faint "ghost" image remains; unsure about completion of bleaching, I leave the film for 9min; nothing much happens. Second test strip with HCl increased to 1% (final) concentration. Image clears in ~1min, leave it up to 3min for good measure. Wash; supposed to remove yellow stain; after ~20min, yellow stain (and ghost image) still there; quick google, prepare 25g/l sulfite solution, that removes yellow stain in ~5min; ghost image still there.

Proceed to re-develop in Dektol 1+4. 5 mins, 10 mins, nothing happens. Dump Dektol, try HC-110 dil.B. Same thing. Film will not re-develop; I'm stuck with the faint ghost.

What did I do wrong? Is it possible to over-bleach? I thought it was a reaction done to completion, and nowhere did I read that I should snatch the film out as soon as (as what?). Advice welcome; specific and fact-based even better. Thank you.

 

[David Allen]

25g/l sulfite solution that removes yellow stain

Hi there,

Here are your problems:

• Bleaching should be done until the image is no longer to be seen and there is a yellow stain.
• Washing (in PLAIN) water should be long enough to remove the yellow stain
• For effective results with Chromium Intensifier you need to redevelop in a non-staining print developer such as Dektol for 8 to 10 minutes or until the highlights no longer get denser. You should not use developers containing a high concentration of sulfite.
• You stated that you diluted the concentrated Hydrochloric Acid 1:10 (as a working stock) and then added it to your 200ml working bleach solution. This means you have diluted the Hydrochloric Acid 1:10 and then diluted it again 1:40 so you have practically no Hydrochloric Acid in your bleach. For 200ml of working bleach you need 0.5ml of Hydrochloric Acid for effective results.
• Also, I was always taught that you should mix the chemicals fresh before use and the working solution should be 1L. I am no chemist (so I do not know if this is accurate) but I was told that there is a minimum amount of Hydrochloric Acid required in the bleaching bath and that mixing less in proportion would not work (have never tried this myself).

By the way, I trust that you are taking effective preventative measures to protect your health as this stuff is pretty toxic.

Finally, are you experimenting with Chromium Intensifier as a learning process or are you wanting to rescue a thin/flat negative? Several other options are open to you:

• Selenium tone your negative in a strong solution (1:10) for ten minutes with constant agitation.
• Use Dokumol at 1:6 as your developer when making prints and develop for at least 2 minutes for resin papers and at least 3 minutes for fibre papers (provided, of course, you safelight set-up is safe).
• Use a combination of both.

Bests,

David
www.dsallen.de

 

[bernard_L]

Hi there,
Here are your problems:

David,
Thank you for your long response. However, you do not fully answer my question(s).

Bleaching should be done until the image is no longer to be seen and there is a yellow stain.

I left the strip of film in the bleaching solution at least twice the time when nothing seemed to change any more. See actual times in my initial post. Question: can one bleach too long? Like, time for (ordinary) development is critical; time in fixer can be 2x normal without adverse effect (except maybe FB paper will need longer wash)

Washing (in PLAIN) water should be long enough to remove the yellow stain

20 minutes washing and yellow stain still there. Would be helpful for me to know what is, normally, the time for the yellow stain to disappear.

in a non-staining print developer such as Dektol

Not part of my problem; as I stated: "Proceed to re-develop in Dektol 1+4. 5 mins, 10 mins, nothing happens"

(...)This means you have diluted the Hydrochloric Acid 1:10 and then diluted it again 1:40 so you have practically no Hydrochloric Acid in your bleach. For 200ml of working bleach you need 0.5ml of Hydrochloric Acid(...)

Please check: 5ml of HCl stock (pre-diluted 1/10) is the same as 0.5ml of concentrated HCl.
This is for concentration of HCl. As concerns the totoal quantity, in 200ml working strength bleach, I treated in total four (4) frames of 24x36mm (as explained in my original post), don't expect to come close to exhaustion, or else, how much bleach would be needed for one 135 film or one 4x5 cut film?

(...)Selenium, Dokumol, both...

Selenium toning was my first test strip, plan to measure with densitometer, but visually I guess I'll gain 1/2 paper grade. Dokumol I have, and indeed my plan is to combine both. But my question was about chromium intensification.

By the way, I trust that you are taking effective preventative measures to protect your health as this stuff is pretty toxic.

You are correct. Rubber gloves. Reduced Cr(+6) to Cr(+3) (green) with sodium sulfite before dumping at end of test session.

Best,
Bernard

 

[David Allen]

Hi there,

Bleaching should take 8 – 10 minutes.

You follow this with 5 minutes wash in continuously changing water.

The 25g/l sulfite solution was a mistake - only PLAIN water is used for the wash.

Please check: 5ml of HCl stock (pre-diluted 1/10) is the same as 0.5ml of concentrated HCl.
This is for concentration of HCl. As concerns the totoal quantity, in 200ml working strength bleach, I treated in total four (4) frames of 24x36mm (as explained in my original post), don't expect to come close to exhaustion, or else, how much bleach would be needed for one 135 film or one 4x5 cut film?

Whilst the maths are correct what you (and I) do not know is what is the minimum amount of Hydrochloric Acid required within the bleach. By this I mean that, as is the case with many formulas, there is a minimum amount (not percentage) of a particular chemical required.

I would suggest mixing up 1L of the bleach EXACTLY as per the formula and redo your tests. If you want to work with smaller quantities, still mix up 1L as per formula and decant into smaller brown glass bottles.

Bests,

David.
www.dsallen.de