Lesson #22: 'Flipping' sheets during printing
(contributed by Dave Bull)
These lessons have talked about 'water' before, and will no doubt do so again and again as time goes by. Water control is at the heart of the traditional Japanese process. And today we come back to water once more ...
Keeping the sheets at the appropriate level of moistness involves a bit of a contradiction - if any sheet was 'just right' at the moment of printing any particular colour, then as it picks up the impression of wet pigment and paste, doesn't it absorb that moisture and thus become too wet for the next impression?
This can indeed happen. If the area being printed is wide, and the particular type of impression being taken is one that uses quite a wet mix of pigment, the paper does become too wet for the next impression, and sheets of newsprint cut to the same size as the print must be inserted between each sheet in the stack for a few minutes to pull out some of the excess water. But this is relatively rare. Is is usually the case that the water being added by the printing is generally balanced by water being lost during the process - by evaporation from the sheets being waved about in the air while coming onto the block and from the newsprint or cardboard covering the stacks of waiting and finished sheets.
What is more common than an overall excess of water, is for the moisture to become unbalanced across the breadth of the sheets. Imagine a sheet being printed with a landscape scene - when doing the sky colour, every sheet gets moisture added to it only at the 'top' of the paper. If these sheets are stacked up in a normal way, all that 'new' water will be in one area and it will take many hours for the water to equalize across the stack. But if one stacks them 'heads and tails' with alternate sheets upside down, there will be no such problem, and the moisture will remain properly balanced.
It's a bit troublesome to handle such a stack of paper when it comes time to print the next colour, as the upside-down sheets have to be flipped round for printing again, but there is no question that it saves the paper from becoming saturated in some places while remaining too dry in others.
'Heads and tails' - it works for sardines ... and woodblock prints!