Hi,
As promised, here are the details of the process I've reached so far. I say "so far" because all things are subject to tweaking! To measure the chemicals by weight I use a small digital balance that reads to 0.01g (how accurate it is, I don't know, but if the first d.p. is accurate, that's probably good enough as long as it's consistent. I bought the balance from a jewellery shop for £20. As has been said, local issues such as water characteristics and individual ways of working will have an effect on the end results, but for what it's worth, here goes:

Black and White Reversal Process for Ilford FP4 exposed at 125ASA.
Check List.
Ilford PQ Universal developer
Stop bath
Fixer
Thermometer
Gallon of water at 20 degs C
Potassium Permanganate 0.8g
Sodium Bisulphate 11g
Sodium Metabisulphite 12.5g
Hypo stock solution 20g in 200cc water (equates to 10cc per gram hypo required)
Lamp with 100W bulb

All at 20 degs C until final wash.

1) Pre-soak for 5 mins.

2) Develop Ilford PQ Universal 1 + 5 + 4g/l hypo.
Invert twice each 15 secs for 10 mins.

3) Stop bath 1 min (not in Ilford procedure – see note below)

4) Water wash (Ilford recommended procedure)
Invert 5 times, discard.
Invert 10 times, discard.
Invert 20 times, discard.
Invert 20 times, leave film soaking whilst making up bleach, then discard.

5) Bleach – 11g Sodium Bisulphate dissolved in 400cc water, then add 0.8g Potassium Permanganate – 5 minutes continuous agitation.

6) Water wash (Ilford recommended procedure)
Invert 5 times, discard.
Invert 10 times, discard.
Invert 20 times, discard.
Invert 20 times, leave film soaking whilst making up clearing bath, then discard.

7) Clearing Bath – 12.5g Sodium Metabisulphite dissolved in 400cc water
Invert twice each 15 secs for 2 mins.

8) Water wash (Ilford recommended procedure)
Invert 5 times, discard.
Invert 10 times, discard.
Invert 20 times, discard.
Invert 20 times, discard.
9) Second exposure – underwater in translucent plastic jug, 12” from 100W incandescent lamp, moving constantly and evenly. (Ilford say remove from reel, but I leave film in my translucent white plastic Paterson reel with no problems).

10) Second developer – Ilford PQ Universal 1 + 9, 6mins

11) Stop 1 min

12) Fix

13) Rinse @ 20 degs C then reduce rinse in stages of about 3 degrees to tap water temperature. Wash 20 mins.

14) Dry.

Notes.

a) Hypo is supplied in large crystals, so a larger quantity in a stock solution seemed more accurate. Ilford recommend 12g/litre, which I found excessive, leading to blown light areas and lack of blacks.

b) Ilford recommend that the “time and temperature be closely monitored if consistent results are to be obtained”. Given that, why do they not suggest a stop bath to arrest development? Their application sheet (2003) says that the acid bleach “stops development immediately” ... hmmmm .... only after the 5 mins wash process, though!

c) Bleach – dissolve Sodium Bisulphate first at it doesn’t dissolve readily and once the permanganate has been added you won’t be able to see whether the bisulphate is all in solution. Ilford procedure uses sulphuric acid but this is Existing Light’s recipe. Though some say this softens the emulsion unduly, I haven’t found it to be a problem as I leave film in the reel for 2nd exposure.

d) From completion of bleaching, the process can theoretically be continued with the top of the tank removed though I don’t do this as I prefer to regulate the second exposure later on. Don’t ask me why – I just do!

e) I prefer to make up the bleach and clearing solutions when I get to that part of the process, largely because I don’t have much space. I check and correct the temperature of these as necessary, though I suspect I’m being over-cautious.

f) The translucent white plastic reel allows sufficient transmission/reflection of light, but I suspect that a black Bakelite reel would give rise to unexposed areas.

g) Time – allow about two hours for the whole process, as there are many stages and weights/volumes to measure. However, apart from the first development stage, the rest of the process can be completed in easy time, stopping to make a cup of tea, take a breather from all the inversion agitation, etc. during one of the many washing procedures, as required!

Good luck and I hope to hear how others get on with the process.

Steve