- 0 = extra soft (= very diffuse grayish )
- 1 = soft
- 2 = special
- 3 = normal
- 4 = hard
- 5 = extra hard (= almost only black and white)
For black and white processing, photo papers with fixed or variable gradation are used.
Paper with a fixed gradation is exposed to white light.
Papers of variable gradation are exposed to filtered light. They react to yellow light with low contrast (gradation 00 or 0), to magenta light with high contrast (gradation 5). Foil filters, which are inserted into the beam path of the enlarger, are available in mixed colors of yellow and magenta, so that half gradations can be achieved. Enlargers with a multigrade module have infinitely adjustable filters.
With the split-grade technique, a yellow, then a magenta-colored filter is swiveled in first. Intermediate stages are achieved by varying the exposure times for each of the two filters.