First posted 12 March 2010
Split Grade printing in it’s most basic form is a process whereby two exposures are given, one through a Grade 5 filter and one through a Grade 00 filter. These two exposures can be varied in order to arrive at the correct contrast for almost any negative. I have another, simpler version which I will write about at a later date, but for now I’ll explain this method.
As I said, there are two exposures given, one through a Grade 5 and one through a Grade 00. That is the theory anyway, -but in reality some negatives only need one filter to print. This is especially true with extremely thin negatives which can only be printed on a Grade 5.
Let’s go back to basics: To simplify, the photographic emulsion in a Variable Contrast or Multigrade paper is made up of two light sensitive layers. One is sensitive to green light and gives a long range of greys from pale white through to dark grey, it won’t give a deep black unless it’s grossly overexposed. The other layer is sensitive to blue light and gives a very high contrast result, consisting of mainly black and white, with very few intermediate tones.
White light gives roughly equal amounts or both green and blue light, so exposing without a filter activates both layers giving a contrast between the two extremes, -roughly grade 2, depending on enlarger type. Using a Grade 2 filter also activates both layers equally, but reduces exposure time because of the density of the filter.
When two different exposures are given, one of the layers is activated more than the other and this moves the contrast away from grade 2.
Because this subject needs a full explanation beyond the space I have here, I have made a demonstration video which should make the point more clearly.
The video is currently unavailable, but I will restore it soon and give the link here. Please accept my apologies.