I'm still trying to plough through the minefield of B&W reversal processing. If anyone has experience of this product or any other commercially available one I would appreciate comments or advice. I am determined to produce B&W slides over the Summer and need to determine the best method for consistant results.

Thanks

Chris Moyse.

-- Chris Moyse (chris@cmoyse.freeserve.co.uk), March 16, 2000

Answers

Here is a response I received from Ed Inman. Reversal processing is not for the faint-hearted. Be very careful with these chemicals:

You can try the Kodak kit which uses permanganate bleach and a direct blackening redeveloper requiring no re-exposure, or you can use this more traditional procedure which works well with most B&W materials:

SUGGESTED SOLUTION FORMULAS:

FIRST DEVELOPER: Add 9.5 grams of sodium thiosulfate to 1 liter of Kodak D-19 developer regular strength.

BLEACH: To one liter of water add 9.5 grams of Potassium Dichromate and 12 ml of concentrated Sulfuric Acid.

CLEARING BATH: To one liter of water add 90 grams of Sodium Sulfite.

SECOND DEVELOPER: Use straight D-19 or a standard paper developer like Dektol.

FIXER: Use Kodak Rapid Fixer or similar.

HYPO CLEARING AGENT: Use Kodak Hypo Clearing Agent, or similar.

PHOTO-FLO: Use Kodak Photo-Flo or similar.

These solutions can be used to make B&W slides from almost any 35mm B&W film. The recommended starting point times for a standard (non- rewind) tank at 20C (68F) is:

FIRST DEVELOPER: 7 min. RINSE: 2-5 min. (change water frequently) BLEACH: 1-2 min. CLEARING BATH: 2 min. RINSE/RE-EXPOSE (Take film from tank and expose to white light. You can't overexpose at this point) SECOND DEVELOPER: 5 min. RINSE/FIX/DRY normally.

Use of fixer is optional. Film can be washed and dried after second developer but emulsion will remain unhardened.

As a general rule, just remember: If too dark, increase time or temp. of first developer. If too light, decrease time or temp. of first developer.

TO ORDER HARD-TO-FIND CHEMICALS call Photographer's Formulary toll free at 1-800-922-5255. (Note: They only sell sulfuric acid in a 48 percent solution so you will need to use 25ml for a liter of bleach INSTEAD of the 12ml you would use of concentrated solution.)

DISCLAIMER: Potassium Dichromate and Sulfuric Acid are hazardous chemicals which should be treated with extreme care and handled as hazardous waste. If in question, the bleach formula should be made by a qualified chemist.

-- (edbuffaloe@unblinkingeye.com), March 16, 2000.

Crikey Ed, did you find that formula for bleach on a stone tablet? Modern sequestering agents like EDTA (EthyleneDiamineTetraAcetic acid) are much safer and probably easier to obtain. It's what all these new-fangled colour reversal processes use.

-- Pete Andrews (p.l.andrews@bham.ac.uk), March 17, 2000.

Well, I've searched the web for alternatives, but most sites still give the old bleach formula that uses sulphuric acid and potassium dichromate. Here is another such:

ILFORD TECHNICAL DATA - REVERSAL PROCESSING OF ILFORD NEGATIVE FILM Reversal processing enables black and white transparencies to be produced directly from ordinary negative materials exposed in camera the normal way. The basic reversal process starts with development of the negative image. At this point the used silver halide is not fixed out as in normal film processing, but completely bleached away, using an acid bleach (see warning). This leaves the remaining silver halide ready to be light-fogged and then re-developed to form the final positive image. Between the various stages of the process, washes are used to prevent contamination of each new processing solution by the previous one. There is only one critical stage in reversal processing; the first development. The first negative image must "use up" just the right proportion of the emulsion, so as to leave behind the correct amount of silver halide to give the desired positive image at the end of the processing sequence.

RECOMMENDED FILMS The suitability of a negative film for reversal processing depends largely on its inherent contrast. Little can be done to change the contrast appreciably by changes in processing. So choose a film for reversal processing according to the ultimate contrast required in the final positive image. For this reason FP4/FP4 Plus is recommended for a moderately soft graduation image with pleasing tones. PAN F gives somewhat higher contrast and pleasingly bright positives. Particularly suitable for copy slides of photographs. We do not recommend reversing high speed films, as they are likely to be too low in contrast.

REVERSAL PROCESSING PROCEDURES These are two methods available to make transparencies from black and white films. These are Kodak's T-Max 100 Direct Positive Film Developing Outfit and a user prepared procedure. Each has its own unique quality, but work on the same principals. Black and white reversal processing involves six main stages: 1. First development - here the exposed image is developed to a negative. 2. Bleaching - here the negative image is completely bleached away. 3. Clearing - this is to clear away all traces of the powerful bleaching bath, and the slight stain it leaves behind. 4. Re-exposure - this is a total fogging exposure to make the remaining silver halide readily developable. 5. Second development - all the residual silver halide is developed fully, to form the positive image. 6. Final fixing - this is an optional stage which removes any last traces of silver halide that did not develop and leaves the image clean and fully transparent in the clear parts.7. Final washing and drying are quite normal. T-MAX 100 DIRECT POSITIVE FILM DEVELOPING OUTFIT When using this kit, we would recommend the following exposure modifications coupled with the corresponding development times. The times are given for first development and are a GUIDE ONLY. Modification may be needed depending on the output required.

FILM EXPOSURE (STOPS) FIRST DEVELOPMENT TIME PAN F +1 3 minutes FP4 Plus +1 6 minutes 400 DELTA* +2 6 minutes *May produce transparencies of low contrast. USER PREPARED REVERSAL PROCESSING PROCEDURE - SOLUTIONS REQUIRED A. Developer - Use either ILFORD Bromophen 1+1 with water or ILFORD Universal Paper Developer diluted 1+15 with water. To one liter of the working strength developer add Sodium Thiosulphate crystals (hypo) in the following proportion: PAN F 8g FP4/FP4 Plus 12g B. Bleach - Mix the following solution: Potassium Dichromate 10g, water 1 liter; when dissolved add, slowly and carefully, 10ml of Sulfuric Acid (concentrate). As you pour in the acid to the dichromate solution, much heat will be generated, so pour in the acid very slowly and carefully.

IF IN DOUBT, ASK A QUALIFIED CHEMIST TO MIX THIS FOR YOU. Protect your skin and eyes by using rubber gloves and protective eye wear. ********************************************************************** WARNING!! Concentrated Sulfuric Acid is DANGEROUS and HIGHLY CORROSIVE!! ALWAYS pour the acid into the water, and NEVER the water into the acid! KEEP OUT OF THE REACH OF CHILDREN!!! CAUSES severe burns. May be fatal if swallowed. DO NOT get into eyes or onto skin or clothing. Keep out of the reach of children. In case of contact: EXTERNAL: IMMEDIATELY flush with tap water, then water containing sodium bicarbonate. INTERNAL: DO NOT give an emetic. Give whites of eggs beaten with tap water, milk of magnesia or milk. GET MEDICAL ATTENTION AT ONCE

C. Clearing solution - Sodium Sulphite (anhy) 50g. Water to 1000ml. D. Second Developer - It is most exonomical to re-use the first developer over again. This is not ideal because of the added (but unwanted here) solvent. Ideally you would used the same developer, but without the added Hypo. E. Final Fix - Universal Fixer 1+9 or any other available fixer. THE REVERSAL PROCESS SEQUENCE 1. First development 12 minutes 2. Wash 5 min., perferably running water 3. Bleach 5 minutes 4. Rinse 1 minute 5. Clear 2 minutes 6. Rinse 30 seconds 7. Second exposure 30-60 sec to white light 8. Second development 6 minutes 9. Rinse 30 seconds 10. Fix 1 minute 11. Final wash 10 minutes 12. Dry This file was made available through the courtesy of Ilford Corp.

-- (edbuffaloe@unblinkingeye.com), March 17, 2000.

The formatting didn't hold on that last post, but the info is at ftp://vmsftp.rit.edu/pub/ritphoto/photoforum/faq-27.

-- (edbuffaloe@unblinkingeye.com), March 17, 2000.

Pete says: Crikey Ed, did you find that formula for bleach on a stone tablet? Modern sequestering agents like EDTA (EthyleneDiamineTetraAcetic acid) are much safer and probably easier to obtain. It's what all these new-fangled colour reversal processes use.

Actually EDTA will not accomplish the bleach step. EDTA is a chelator of divalent cations. What you need for a bleach is a strong oxidising agent. In color reversal (E6) there is no bleach step between the developers. There is a first developer that is basically a black an white developer, followed by the second developer that incorporates the color couplers. When the two developers are finished in E6, the silver image is totally black and is subsequently bleached away leaving the color image. In black and white reversal processing you need to remove the negative image completely before developing the positive image. Permanganate and Dichromate will oxidize the metalic silver (Ag(0)) to the silver cation (Ag(I)). In the case of reversal processing bleaches the counter ion is sulfate. The silver sulfate is soluble and thus washes out of the emulsion. If you look through your formulas at the reagents used for chrome intensification, you will see that the bleach there is potasium dichromate and hydrochloric acid (HCl). In that case the counter ion is chloride and the resultant AgCl is insoluble and remains in the emulsion to be redeveloped in the intensified negative.

One note on the bleach formula listed in Ed's posting. It is probably safer to use bisulfate instead of sulfuric acid in the bleach. The reason that I say that is that sulfuric acid is a liquid and for a home darkroom situation having it around lends itself to the possibility of spills and potential injury. Sodium bisulfate is a solid and this easier to contain and clean up in the event of a spill. My formula for dichromate bleach is 9.6 grams potasium dichromate plus 66 grams sodium bisulfate in 1 liter water. I didn't design this recipe myself, I got it from somewhere that I cant remember. The original is probably floating in cyberspace somewhere. Remember, though, this bleach solution is plenty nasty, even though you used bisulfate instead of sulfuric acid. Use rubber gloves and avoid contact with this particular solution.

Concerning the choice of first developer, to get optimal results you need to match your first development conditions to the film you are using. As an example, my favorite film for reversal procesing is TechPan. Everywhere you go you will see admonitions that TechPan is too contrasty to use for anything except lettering or line art. But by twiddling with the first developer I have gotten TechPan to work very well for general pictorial reversal processing and I use it almost exclusively. Using a D19 based first developer, though, it would never give acceptable results. So, the moral of this passage is to get optimal results, you need to put in the time experimenting. But that is what makes this an art form after all, isn't it?

-- Fritz M. Brown (brownf@idhw.state.id.us), March 20, 2000.

For the sake of accuracy, I noticed a mistake in my responce above. The second developer in E6 contains the color developer (ie CD3). The color couplers are in the emulsion already. The color developer is what links the reduction of the silver to the conversion of the color couplers (presumably by oxidation) and development of the color image.

-- Fritz M. Brown (brownf@idhw.state.id.us), March 22, 2000.