What it is
Papers differ first of all in what they have on the surface. A coated paper has a mineral layer spread over the fibre: it closes the pores, makes the surface smooth and uniform, and the ink stays on top of it. Hence crisp halftone dots, fine detail and a wide colour gamut. An uncoated paper has no coating: the fibre is exposed, the ink penetrates, the dot spreads, colours look more muted and the white is less bright. That is not a defect, it is exactly what the designer is after when choosing it. In between sit the matt and silk papers, which close the surface without giving back the reflection of a gloss sheet.
Then there is bulk, the most misunderstood word in the trade. It does not mean roughness: it means specific volume, that is, how much thickness is obtained for a given grammage. A high-bulk paper at 120 g/m² has more body than an ordinary paper of the same weight: it costs less to ship and it feels more important. Finally there are the worked surfaces — embossed, felt-marked, laid — and the through-dyed papers, coloured in the stock and not on the surface. On these papers the print is not laid on a flat plane: fine screens suffer, solids can come out mottled and finishing behaves less predictably. That is the price of character, and it has to be allowed for beforehand, not discovered during the print run.
How to prepare the file
- Ask prepress for the printing condition appropriate to the paper family: using a coated profile on an uncoated paper means promising a colour that substrate cannot deliver.
- A proof on the correct simulation and, on delicate jobs, a control print on the real substrate before the print run is launched.
- On uncoated papers, check reversed-out text at small sizes and fine knock-outs: dot gain tends to close them up.
- On embossed or heavily textured papers, rely less on fine detail and light halftones, and ask for a foil or varnish sample before deciding.
- Check opacity and grain direction against the grammage: show-through from the reverse is discovered once the job is printed, when it is too late.
What can go wrong
- The monitor and the proof on glossy paper always mislead in the same direction. The client has to be brought to the physical sample before approval, not after delivery.
- Speciality papers come with variable availability and variable batches, and the shade can change from one batch to the next. On repeat work this has to be provided for in the contract, not simply put up with.
- Not every finishing process holds on irregular surfaces. Hot foil stamping and lamination on heavily textured papers give results different from the ones expected: they are trialled first.
Frequently asked questions
- Why does the same file look duller on uncoated paper?
- Because the ink penetrates into the fibre and the white of the paper is less bright: the colour gamut is objectively narrower. With LED-UV the gap narrows, but it does not disappear.
- What is the bulk of a paper?
- The ratio between thickness and grammage. High bulk means more body for the same weight: it gives substance without adding weight.
- Can I use a speciality paper for a folding carton?
- Often yes, but it has to be checked first. Stiffness, behaviour under creasing and glue adhesion cannot be deduced by looking at a flat sample sheet.