Kevin O'Brien (kob@paradise.net.nz)
Sun, 21 Feb 1999 12:13:40 +1300
Hi all,
Reversal is easy to do, making a neg for printing out on self masking
materials like Pt/pd or kalitypes is not. One old source says:
"The negative which prints perfectly in platinum is one which has been
exposed for the shadows and has been developed until the surface of the
plate appears to have lost its image."
Luckily I made some by accident but not by the simple way copying neg ->
interpos -> neg -> print. I tried various films for reversal, these 1982
notes show some of the problems and results:
Verichrome pan 125 - Good gradation & tone, bad reticulation in mid
tones, chewedl way, interesting graphic effects. Process: Rodinal (Agfa)
1:15 10' with hypo 9ml, bleach std, redev rodinal 1:20
Plus X prof 125 - Good gradation, slightly overposed suggest ½ stop,
sharper, more detailed, slightly grainy- worse than FP4, 10x grain crisper,
watch hardening, tends to scratch. Process: Rodinal 1:15 12' with hypo 6ml,
redev rodinal 1:12.5 2films. Pre-bath hardener: formalin 2%.
FP4 125 - Slightly contrasty, highlight thickness, need for bleach
subsequently, tends to frill but hardening may fix it.
PX - Thin neg and dense highlights i.e overdeveloped, gradation not bad.
Process: Bromophen 1:2 5' with hypo 6ml, ½bleach
FP4 - Dmax thin, good gradation. Process: Rodinal 1:15 with hypo 21ml,
bleach ½std, redev Ultrafin 1:10 ( a Tetanal product), acid hardener, no
pre-bath. GOOD
PXP - Development contd while bleaching, some remains at re-exposure
stage, took it out of bleach part way through for inspection, lightly
fogged. This was then bleached after completion so overall density reduced.
Appears OK otherwise. Process: Rodinal 1:15 with 6ml hypo, bleach ½ std,
redev rodinal 1:25, hardens good, no pre-bath.
VerPan - Thin and grainy, grain related to thiness. Process: Rodinal
1:15 10' with hypo 5ml, bleach ½std 5', clear by inspectio 1', redev rodinal
8'.
VP250 - reticulated, could it be the fix? Process: Rodinal 1:15 with
hypo 7ml 9½', bleach ½std, full secondary exposure 4', redev Microphen full
strength - slow but OK, finished off Bromophen1:1, 2'. Acid fix, hardener:
colour film conditioner (formalin bath).
Agfapan 100 exp200 - Very dark and contrasty, soft gelatin at start but
OK on drying (could try fix without hardener). After treatment with weak
ferricyanide to give good transparency. Good gradation at 100ASA. Try again
with extra hypo or re-use first developer. Process: Rodinal 1:15 with hypo
4ml, bleach ½std, full secdry exp. redev Bromophen 4½', very acid fix, film
conditioner.
Agafapan 400/400 - Bit thick, highlights not cleared. Used .... ? but
bleach selective. Good surface, soft gradation but OK. Process: Rodinal 1:15
with hypo 5ml, 10'. Bleach: Pot dichromate 45ml/10%soln, sulph acid (conc)
6ml, water to 500ml. Clearing sod metabisulphite by inspection.
Chemistry:
Hypo: Sodium thiosulphate 25% soln (not fixer, but just the plain
tradtional hypo crystals in solution).
Bleach (standard):
Pot permanganate 1g
Sulphuric acid conc 5ml
Water to 500ml
(For ½std increase water or reduce chemical quantities to half.)
Or, as I mixed it, for ease of use:
16ml of 25% pot permanganate soln
5ml of conc sulphuric acid (these days, try 50ml 25% sod bisulpate
soln instead)
Water to 500ml
Hydrochloric acid can't be substituted for sulphuric in this bleaching
process as the developed silver has to be removed. This is not the same as
the bleach and re-develop for contrast control where the cloride or bromide
is needed to so it can be re-developed. The silver here goes down the sink
as silver sulphate leaving the positive image behind as unexposed film. Pot
dichromate can be substituted for the permanganate and an alternative using
this is:
Stock solns:
Pot dichromate 5%
Sulphuric acid 5%
To use pour 5ml of each into a 1litre of water. (Don't worry about 5%
strength sulphuric, it doesn't taste nice, but doesn't cause any dramas).
Bleach until silver disappears - about 5 mins.
Another SAFE one (Weber):
Pot dichromate 6g
Sod bisulphate 20g
Water to 1l
Clearing bath:
I didn't record any for the permanganate bleach so it probably wasn't
needed.
The dichromate does need it: 5% sod sulphite, 5 minutes (Kodak CB-1 has 9%
soln). Some films are sensitive to clearing.
Hardener: Formalin 2%
Fogging: some peculiar chemical can be used but they may cause havoc
elsewhere around the darkroom as well as being difficult to obtain and
expensive. Bright light is needed for complete fogging and this is best done
under water: 1min 30cm from a 100w light. May need several minutes if
further away. Too much can be given.
Some of the direct positives may have been capable of producing an excellent
negative but not on lith processed as contone. If I had a proper contone
film with a long scale and a suitable developer it probably would have been
practical with a softer transparency developed out fully. The Agfa N31 would
be a good choice. Kodak commercial 4127 and probably the new Aristatone
from Freestyle may be suitable.
Lith film is to be avoided if the direct process is to work. It is made for
a purpose to form black or white, which is why the pinholes appear. The
grains of silver in it have been designed to clump together by
infectionously joining with adjacent ones during development and some
interesting graphic affects can be had with different developers. Lith film
has to be distinguished from contrasty continuous tone film which does not
develop that way and where the tonal character can be changed. Ortho films
typically are fairly contrasty.
Kevin O'Brien
Wainuiomata, NZL
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