Machine or Grain Direction in Paper

Paper Curling
Paper Curl­ing

You might have noticed that when you tear a square from a sheet of paper, one dir­ec­tion leaves a nice clean edge but the edge is much more ragged on the right-angled tear.  You’ll have also spot­ted that when fold­ing A4 sheets in to A5 book­lets there’s a strong tend­ency that the book­let will spring open.  Paper dis­plays dif­fer­ent qual­it­ies depend­ing on wheth­er you’re work­ing in the dir­ec­tion of the ‘grain’ or ‘across the grain’.

Because paper is made from long fibres of one form or anoth­er, there is a tend­ency for paper machines to draw these fibres in to the machine in a par­tic­u­lar dir­ec­tion.  Nat­ur­ally paper­makers look to avoid this but even in fine papers you’ll end up with long fibres run­ning in the same dir­ec­tion as the paper machine runs.  This is the ‘grain dir­ec­tion’.  There’s no firm rule about which dir­ec­tion the grain will run in any giv­en pack­age, but paper mer­chants tend to cut the paper so that the grain runs from top to bot­tom.  On lar­ger sheets that you might buy dir­ectly the grain could run in either dir­ec­tion.

There are two simple tests to find grain dir­ec­tion.  If you tear the paper once and again at right-angles, you’ll see that the tear looks dif­fer­ent: with the grain will leave a much clean­er tear; across the grain will leave a more messy tear.  Altern­at­ively you can cut two sim­il­ar pieces of paper around 2″ x 6″ at right angles to each oth­er and put them togeth­er.  Hold­ing one end out you’ll find that one might flop and anoth­er seem more strong; if not one might be ‘sup­port­ing’ the oth­er.  This ‘sup­port­ing’ or stronger piece will have the grain run­ning down the length of the paper.

Grain dir­ec­tion will affect tensile strength; rigid­ity and sta­bil­ity.  The degree to which these affect us will depend on the spe­cif­ic paper and maker so there are no con­crete rules on how big a prob­lem this might be for you.

Strength will be most import­ant in some spe­cial­ist applic­a­tions: bottle labels, for example, are applied left-to-right on the bottle and so are pulled from left-to-right by the labelling machine.  Because the paper will be strongest with the grain, it should be prin­ted so that the grain runs from left-to-right.  Oth­er areas might include hole punched doc­u­ments that might be sub­ject to pulling from left-to-right.

To pre­vent ‘spring­ing’ when a book­let is opened; the grain should run par­al­lel with the spine.  Look out for this if you intend to print, say, an A5 book­let from A4 because the A4 is usu­ally sold with the grain run­ning from top-to-bot­tom.  Using this will lead to the fol­ded book­let spring­ing open.

Rigid­ity is import­ant where prin­ted art­icles have to be handled or stored upright.  Index cards, for example, need to be prin­ted with the grain run­ning from top-to-bot­tom as this will mean the card is strongest in this dir­ec­tion, and so avoid the cards flop­ping down or curl­ing slightly.  Clock­ing-in cards should be prin­ted with the grain run­ning top to bot­tom to help with the hand­ling of the cards.

Finally, sta­bil­ity rests on the tend­ency of paper to take up water from its sur­round­ings.  When this hap­pens the paper swells across the grain because fibres have a tend­ency to expand in their width rather than length.  This is most import­ant when doing very close register work or col­our print­ing.  There may be a dir­ec­tion where the register is less import­ant.  One example would be ledger sheets where top-to-bot­tom register is less import­ant than the need to get left-to-right columns cor­rect, for a change in these could lead to mis­taken use of the wrong column.  In this case, if the tol­er­ances are very tight, con­sid­er­a­tion should be giv­en to have the grain run­ning left-to-right across the page so that any expan­sion in the fibres has an effect top-to-bot­tom rather than left-to-right.

All of these con­sid­er­a­tions seem small in com­par­is­on with machin­ing or the ini­tial lay­out but it’s these small details that will make the final job look and feel bet­ter than one without con­sid­er­a­tion of the grain dir­ec­tion.