Quote Originally Posted by Michael R 1974 View Post
If I remember correctly not all that long ago Ilford Multigrade filters ranged in colour along a fairly continuous progression from yellow (#00) to a fairly dark magenta (#5). This is similar to most VC heads and Ilford still refers to yellow and magenta filtration in the current tech pub discussing contrast control with MG papers.

However the current generation of multigrade filters are not like this. They seem to be a perhaps more sophisticated set of colours. #00 looks orange. There is then the more or less expected progression to magenta through grade 3 1/2. Then a change in colour again at grade 4 onward, which seems (to the eye) to be less "magenta" than grade 3 1/2.

The only reference I can find in Ilford's online resources is a statement that the previous incarnation of the filters was never able to deliver as low a minimum contrast as the current version. Ilford also indicates the dyes may be less stable in the previous version although it is not entirely clear whether that is intended to mean old filters should be replaced, or if it means the newer versions actually have more stable dyes.

Did the current version coincide with the introduction of Multigrade IV? Does it have anything to do with three-emulsion paper vs older versions?

VC paper is sensitive in two bands, to yellow light for low contrast, and blue light for high contrast. So the question is really how much yellow and blue the filter passes, respectively. My own sets (I have two) are of the old type. How would you describe the colour of grade 4/5 on your new set? More yellow than grade 3.5? That would be strange. If it were somehow more blue, you'd have consider that your eyes and the paper do not have the same spectral response, so it is possible that those filters just have a narrower band pass around the blue frequency. But in all honesty, unless you look at the filter spectral transmission and compare it to the paper's spectral sensitivity, you would be guessing, like I am now.