CIBACHROME FILTRATION

By John Wilson (Area 26) Edited by Arthur McKee

As a newcomer to Ciba I read with interest Mr. & Mrs. Pearle’s article in the April Newsletter.. .1 now add my Fourpence’ worth.This is the well known colour circle The centre is marked  0 and the points representing the colours are equally spaced’ around the outer circle. It shows that  Cyan, Magenta & yellow are the opposites of Red, Green & Blue, respectively.

 

Imagine a small ring suspended at the centre ‘0 by three elastic bands attached to the point: cyan, Magenta & Yellow on

the large outer ring. Let the tension in the bands be proportional to the strength of these colours. If it is equal in each band the, inner ring will be at the centre 0 and represent correct colour, balance. If it is not then the inner ring will move, from the centre towards some point on the outer ring depending on the tensions in. each of the bands, Note that any colour can be represented by a point, on the outer ring. 

Suppose the inner ring moves towards green. Then it is brought back by increasing the tension in the Magenta band or by reducing the tension in the cyan and’ bands. This represents the enlarger light having a green cast which is removed by increasing the strength Of the Magenta filtration or reducing that of the cyan & Yellow filtration equally. If the inner ring moves instead towards a point between Yellow ‘& Red then both the Magenta and Cyan will have to be increased, the Magenta less then the cyan. or the Yellow reduced. 

Getting to practicalities in suggestion is that you use the UV filter only, on your very first test print. Set your enlarger to give a 10 x 8 enlargement and the aperture to F8. Have a black card ready. Switch on your enlarger lamp. Progressively cover the Ciba paper with the black card about 1” at a time allowing each strip an exposure of  2-5-10-5-20-30-40-50-60 seconds until you run out of inches. You should get 9 or 10 if you go along the long dimension. Now develop the sheet in the usual way. You will immediately see which is the correct exposure so at least you have established that and it was the first of your problems. As a bonus you will see the exposure latitude and I was agreeably surprised. However the correctly exposed strip will tell you much more if you at the same time you study the examples of wrong filtration on pages 24/25 of the Ciba Manual Your print when compared to the examples in the book will give a good indication which tinted filters you should add. Expose your next print accordingly. My bet is that it will be at least usable and probably acceptable. Your third print will be and you can now determine your enlarger colour bias. 

Myself, I use an EM10 exposure monitor which I calibrate during the test strip exposure. I find, that it saves paper and I have no regrets at having bought it.

OK! OK! you might say  that is wrong with the method Ilford give on page 14/15? Nothing whatever laddie! if it suits you. But I found the contact print method completely unworkable at the cost of seven sheets of paper. 

My personal experience was that the filtration recommended on my first 10 pack of paper was – Y35: M30: C00.  I actually used Y00 : M00: C45. I worked out my enlarger cum Sakura film colour bias from this and the pack filtration recommendation as follows:-

Y     N     C
00    00   10                     Filtration used on print.
35   30    00                     Recommended Filtration on pack.
35   30    10                     Result of  Subtraction,
35   35    35                     Add 35 right across to remove Negative, values.
00   05    45                     Enlarger/Film corredtion Filtration.

 

 

Cibachrome Filtration (2)

Editorial

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