Quote Originally Posted by Sim2 View Post
*Just musing to myself here really*
I have been aware that the fibre paper swells when wet (and potentially shrinks when drying), I guess that up to actually measuring the print image size I hadn't followed the logical thought process that with the "grain" of the paper fibres going in one direction the actual swelling/shrinkage may not be totally consistent across a sheet. What I think I mean is that if the centre of a print is the reference point the top/bottom and left/right sides may not expand equally by the same amount.

The follow-on thought is that the image on the paper has been stretched/distorted (very slightly) in one measurement e.g. width in relation to the height. Ho hum - good job I don't have to produce a dimensionally "accurate" image of the subject!
This is basically correct. The swell and shrink depend on the fiber orientation and on the stress/strain during drying. On the paper machine, the sheet stretches in the machine direction and shrinks in the cross direction. On re-wetting, the sheet expands more in the cross direction than in the machine direction. The MD/CD fiber orientation of the sheet can varying across its width (as can the stress/strain) so that its wet expansion will also vary. While these generalities apply to most fiber base papers, specifics depend on the actual paper in question.