Scoring is the process of creating a furrow or channel, or ‘crease’ on your printed piece – directly on the fold line (where your piece will fold). It makes for a cleaner fold, and helps prevent cracking along the outside of the folded edge.
While you can score virtually any weight of paper, to assure quality, pieces printing on a cover-weight (thicker) paper – that needs to fold – should be scored on each fold. Cover-weight paper is thicker, and is used for many self-mailers, covers of training manuals, soft-cover books and postcards. If they are not scored on the fold-lines, the result will likely be uneven and sloppy folds, and visible cracking on the outside of the folded edge. The cracking is both from the coating that the paper has on it – often a glossy or matte finish – and the orientation (parallel or vertical) of the score in relation to the fibers of the paper.
Press-scoring often utilizes a plate – similar to a printing plate – that has hard, straight, and thin material glued down in the pattern needed on that plate. This is often used when scoring is required in both orientations (parallel and vertical) on the same piece. The plate comes in contact with the paper, and literally presses the score into the sheet. If the score is along the entire length of the sheet – oriented in the same direction that the paper is moving through the press – wheel scores can be used.
On last thing… if your printed piece will have heavy coverage of ink on it, you really need that score! There’s nothing worse than a large area of dark ink printed over a fold that was not scored. The paper can easily crack along that fold, and white paper (in uneven patterns) will show through. That can ruin the desired look and feel and make the piece look terrible. Even scoring this piece may not eliminate any cracking, but it will minimize it.