Colour order

Similar to conventional offset printing, the colour order plays a role in the reproduction on the risograph. If more than one colour is applied to a substrate, when printing with the second colour on the paper sheet already printed with one colour, it receives a lower amount of coating than the first one from the substrate. This is because it is no longer just the substrate, but also the coating on the paper that was printed first. This may also be due to the fact that the printed colour is still wet when the second colour is absorbed by the paper. It does, however, behave completely different than the substrate regarding the colour acceptance behaviour. Since the inks are translucent and the second printed colour makes the first one visible, swapping the colours in the process print affects the printed colour tone. Similar to the ISOM 2000 recommendation for colour order in four-colour printing (colour order KCMY), if half-tones are printed, the risograph should always print the darker colours before the bright ones. This prevents the lighter colours from becoming spotty on the darker underground and not being able to sink into the paper properly. In the opposite colour order (i.e. first dark, then bright), this makes very little difference. Halftones with scarce pigmentation in light colours, such as midtones in yellow, have fewer chances of sinking into the paper – it nevertheless creates a smoother print image. When determining the order (darklight), however, the following should be noted: in particular, if very dark colours (e.g. black and additionally blue) are printed in the first printing cycle with high ink coverage, the risograph may leave stripes on the sheets when feeding them through the rubber wheel of the paper feed.

In order to avoid this, changing the colour order should be considered (i.e. initially bright, then dark) during the printing process. Reason being that depending on the ink coverage, the rubber wheel could rub on the coating and thus stain the sheets if dark colours have been printed first. If printing with three or more dark colours or if the brightest colour is on the darker side of the scale (eg purple or turquoise green), an adequate drying time should be chosen. This is ensure to both the colour order and the cleanliness of the sheets.