E6. CHEMISTRY
By Lawrence Edwards B. SC., C. Chem. M.R.S.C.
I have been studying and experimenting with E6 since Summer 1987. It took until March 1988 to achieve good results even though I had the advantage of access to a laboratory with precision balance and pH meters. Also the Company I work for manufactures base chemicals like ammonium thiosulphate solution, for the photographic industry. Contacts in the industry were, as expected, only of limited help.
Several months were spent trying to get the British Journal of Photography formula to work but only with limited success. In september 1987 I was
given copies of formulae which appeared to be genuine Kodak E6. I believe thee are the genuine E6 formula from 1977, updated 1980. These are
published in the October 1987 CRCN (Kodak E6/7).The special chemicals were supplied by Mr. B. Wheatcroft. I was somewhat surprised when these formulae gave poor results, i.e. a strong magenta cast. However I now realise that I was unlucky with my selection of AGFA 50S film. I had left the reversal bath at a strength 20% higher than E7 for use with the B.J. formulae. 50RS did not like this. Some experimentors, including B. Wheatcroft, have got these formulae (E7) to work especially with
Ektachrome. I also got fair results with this film but continued to get magenta results with Fuji and 3M.Further progress was made when Melbourne Photographic "Lingcolour" first developer was substituted. This did not solve the problem but helped it eliminated one variable so that Colour Developer could be concentrated on. Also I was given some genuine Kodak E6 chemicals (3.8 Litre size) to
analyse. The results of the chemical analysis were used to modify the E7 colour developer and E7 first developer.Both the Lingcolour and Kodak first developers were similar to the original E7 but were more dilute. Various constituents were tested and results were 84 - 87% of the E7 values. The pH of both was 9.9 - 10 i.e. higher than E7.
The Kodak reversal bath was also confirmed to be in line with the E7 exactly. Stannous chloride content, specific gravity and pH were checked.
The Kodak colour developer was similar to E7 but some differences were found. The CD3 was only 8.0gms/Litre and the pH was 12,0 at 27C. The part B (CD3 Solution) did not contain any metabisulphite. The specific gravity and total alkalinity were also lower than E7.
The conclusion was that Kodak have not changed the E6 chemistry very much from 1980 and the Formulae E7 in the main are still valid. However what they have done is weaken the first developer which will slow it down a little. This has perhaps been compensated for by changes in the colour developer i.e. reduced colour development at the lower CD3 concentration. I believe (but have not been able to test) that the Citrizinic acid content has been reduced to about 0.8gms/Litre to balance the effects of the changes. This mod. will cause increased colour development.
The current specifications for E6 chemistry for machines have been obtained from three sources. There are some differences between the various sources but these are not large. As we know it is the developers that are most important; pH specs. are as follows:
1st. Developer
Col. Developer
KODAK (27C)
9.60 - 9.70
11.93 - 12.03
FUJI (25C)
9.60 - 9.70
11.85 - 11.95
AGFA (27C)
9.55 - 9.75
11.95 - 12.15
It can be seen that the two first developers that I tested had a larger pH than the current machine spec. I have had better results at the higher pH and wonder if this is more appropriate for spiral tank processing and that the 3.8 Litre packs were specially formulated. The colour developer was seen to agree with current specs. for pH (exept Fuji).The modification to the E7 formulae make sense in commercial terms in that a net reduction in chemical costs result. Consumption of CD3, Citrizinic acid, Pot. hydroquinone monosulphonate and Dimezone `S` (the most expensive chemicals) are all reduced.
The modified E7 formulae have rewarded me with some excellent slides and I have to detail a variant of these for the CRCN when they have been
checked out by co-workers. Meanwhile I would be pleased to discuss the E6 chemistry with interested persons.