Trying out Chromium intensifier

[pound]

Trying out intensification myself in this video

Intensification is the process to increase contrast or density of a film or print through the use of chemicals. In this video I explored how can I mix my own chromium using a floor cleaner as a source of diluted hydrochloric acid. I also tried to intensify both photo paper and prints.
Watch to the end to see the results!



https://youtu.be/NpLmktEaqnM

or a digital converted photo of the original negative vs the intensified negative
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[Tin Can]

Thank you.

I will need this technique soon!

[Drew Wiley]

Just be aware that ordinary pool supply or hardware store muriatic acid is still plenty strong enough (around 18% hydrochloric solution) to destroy your lungs if you spill it in an unventilated space. I know a number of people whose health was destroyed for life, and lungs permanently scarred, by using off-the-shelf floor etches carelessly. Either dilute it further down outdoors or use a fume hood.

[Jim Noel]

When I was young chromium intensifier was common. As soon as I knew enough about chemistry to realize it's dangers, I stopped using it. There are other safer methods which also do not amplify grain.

[Bernard_L]

Chromium intensifier allowed me to save a number of negatives obtained many hours of air travel from home (too short dev time indicated by Fuji for D-76 1+1). Selenium toner was not effective enough, by far. Two things I learned while making systematic tests before treating the precious negatives:

Hydrochloric acid from the hardware store was not just good enough, probably some impurity interfering with the intended re-halogenation?
Yellow stain seems to never completely clear by just water washing (between bleach and re-dev). Found the trick in an old Kodak/UK brochure.
Wash thoroughly; then clear in 5% sodium carbonate; rinse; proceeed to re-develop.
This also helped maintain uniform intensification from low (shadows) to high (highlights) densities. Without the clearing step, the intensified negative had a compensating HD curve.

Hope this helps.

[Bernard_L]

Something else. The +6 chromium ion is nasty stuff.
- Beware of dust when mixing (mask)
- Wear gloves when using solution
- Reduce the Cr+6 ions before dumping. Figure out the mass of dichromate in the solution you want to dump. Dissolve twice that amount of sodium sulfite (includes some margin). The solution turns green as Cr+6 is reduced to Cr+3, while sulfite is oxidized to sulfate.

[Tin Can]

Good advice

[revdoc]

A somewhat safer intensification process: a standard rehal bleach of ferricyanide and potassium bromide, followed by redevelopment in a staining developer. This can be repeated any number of times; density and contrast will keep incresing with each cycle.

[domaz]

A somewhat safer intensification process: a standard rehal bleach of ferricyanide and potassium bromide, followed by redevelopment in a staining developer. This can be repeated any number of times; density and contrast will keep incresing with each cycle.

Pyro has it's own problems, but yes it is somewhat safer. Potassium Dichromate is listed as a "4" on the NFPA 704 Fire diamond scale for Health. Meaning "Very short exposure could cause death or major residual injury". Catechol is a 3 meaning "Short exposure could cause serious temporary or moderate residual injury", somewhat comforting I guess?

[koraks]

In my experience there's a limit to the repeated build up of contrast both with chromium intensifier and especially with staining redevelopment. After a few (ca 3) rounds no significant additional density was deposited when I tried it, with chromium intensifier very convincingly being more capable of adding density than staining developers, at least when non-UV printing processes are consequently used.

[pound]

thanks for all the good advice.
Safety is always number 1 when handling chemicals even more when dealing with dichromate and hydrochloric acid.

freestyle is selling a powder kit too here https://www.freestylephoto.biz/050065-Formulary-Chromium-Intensifier-Powder-1-Liter
Looking at the MSDS, it seems to be have potassium dichromate and sodium bisulfate which make it sulphuric acid based rather than using hydrochloric acid.

[Raghu Kuvempunagar]

freestyle is selling a powder kit too here https://www.freestylephoto.biz/050065-Formulary-Chromium-Intensifier-Powder-1-Liter
Looking at the MSDS, it seems to be have potassium dichromate and sodium bisulfate which make it sulphuric acid based rather than using hydrochloric acid.

For the bleach to work as an intensifier, it needs to be rehalogenating - i.e. it should convert all silver to silver halide which can be redeveloped subsequently. This is the reason why hydrochloric acid is used in chromium intensifier as it supplies Cl- ions needed for rehalogenation of the silver by chromium and provides the pH needed for the bleach to work. If sulphuric acid (or bisulphate) is used in place of HCl, the bleach is no longer a rehalogenating bleach. All the silver will be converted by such a bleach to silver sulphate which dissolves in water. This is the bleach we use regularly in B&W reversal to remove the negative image. Maybe Formulary's intensifier also has sodium chloride which is not listed in MSDS as it's not hazardous.

If you're mixing chromium intensifier yourself from dichromate without wanting to deal with hydrochloric acid, you can try this formula that I have used successfully for intensification of b&w slides:

Water: 800ml
dichromate: 10g
glacial acetic acid: 50ml
sodium chloride: 20g
water to make: 1000ml

You can replace glacial acetic acid by lower concentration variety with appropriate changes to volume used.

[Bernard_L]

Interesting, thank you. A question: with regular chromium bleach, the degree of intensification is adjusted with the dilution of HCl, somewhere between 0.5% and 1% from "pure" HCl; less HCl for more intensification. With your alternative formulation, should one adjust NaCl (my bet) or acetic acid?

[pound]

...Maybe Formulary's intensifier also has sodium chloride which is not listed in MSDS as it's not hazardous.
....
If you're mixing chromium intensifier yourself from dichromate without wanting to deal with hydrochloric acid, you can try this formula that I have used successfully for intensification of b&w slides:

Water: 800ml
dichromate: 10g
glacial acetic acid: 50ml
sodium chloride: 20g
water to make: 1000ml

You can replace glacial acetic acid by lower concentration variety with appropriate changes to volume used.
Good information. Indeed there is sodium chloride listed in the Formulary's intensifier MSDS too. I look around the Darkroom Cookbook book but did not find a intensifier formula listed using this 3 ingredients.

Thank you for yr other formula. Looks like I can try household vinegar (5% acetic acid) in place of GAA as that is also hard for me to get hold off.

[Raghu Kuvempunagar]

Thank you for yr other formula. Looks like I can try household vinegar (5% acetic acid) in place of GAA as that is also hard for me to get hold off.

As long as it is pure 5% acetic acid, it should work.

[Raghu Kuvempunagar]

Interesting, thank you. A question: with regular chromium bleach, the degree of intensification is adjusted with the dilution of HCl, somewhere between 0.5% and 1% from "pure" HCl; less HCl for more intensification. With your alternative formulation, should one adjust NaCl (my bet) or acetic acid?

Chromium intensifier works by forming a chromium compound imagewise when the slide/print is bleached. As the bleach is rehalogenating, the original image density is gotten back by redevelopment and the chromium compound adds additional density to it. Thus there is increase in density and it is imagewise - denser regions in the slide/print acquire more density than lighter regions. For rehalogenation to go to completion, there should be sufficient amount of Cl- ions available in the bleach. If the goal is to have control over the degree of intensification, then it is best to partially bleach the slide/print i.e. pick up the slide/print before it is fully bleached, clear, wash and redevelop. In this case, chromium compound will be added only to the extent the slide/print was bleached and the original image density is gotten back.

[mbs88]

verry good advice