When two shapes overlap in a print file, the software makes a quiet decision about what happens underneath. That decision is knockout or overprint, and it changes the printed result.
Knockout leaves a hole
A knocked out object cuts a matching hole in the background beneath it. The press then prints the top colour straight onto bare paper inside that hole. The colour stays pure because no ink mixes under it. A cyan circle on a yellow field prints as clean cyan on yellow.
A carbonless form produces copies with no carbon sheet between the plies. The copy appears because the paper itself carries two coatings, and they react when a pen presses down.
Two coatings, one reaction
The top sheet is coated on the back with tiny capsules, each one holding a colourless dye in oil. The sheet underneath is coated on the front with a clay or resin that acts as a developer. Pressure from a pen or a printer breaks the capsules, the dye spills onto the sheet below, and it reacts with the developer to form a visible mark. Nothing happens until the paper is pressed, which is why the sheets stay clean in the box.
A screen print sits on the surface as a flat patch of colour, thicker than anything an offset press lays down. That depth is no accident. It comes from pushing ink through an open mesh with a rubber blade, and every part of the setup decides how much ink lands.
The mesh is the measuring cup
The screen is a woven fabric stretched over a frame and coated with a light-sensitive emulsion. Where the artwork sits, the emulsion is washed away and open holes remain. A coarse mesh with 86 to 110 threads per inch leaves wide openings and passes a heavy layer of ink. A fine mesh at 230 threads or more leaves small openings and lays down a thin, detailed film. Two screens with the same count can still differ, because thinner threads leave more open area and carry more ink.
A sheet of labels looks like one flat printed page. Peel a sticker off it and only that sticker comes away, with the rest of the sheet still sitting neatly in place. That behaviour comes from a cutting method called kiss cutting, where the blade goes through the sticker and the glue but stops at the liner underneath.
Cutting depth is the whole trick
Kiss cutting uses a steel rule die bent into the shape of the label. The die is mounted on a cylinder or a flat bed and pressed against the printed sheet until the rule cuts the face material and the adhesive layer. The blade must stop before it reaches the liner. Too shallow and the sticker is still attached and tears when it is peeled. Too deep and the liner is scored or cut through, which lets the sheet fall apart on the press and defeats the purpose of a release liner.
Most small print jobs do not fill a printing press. A run of business cards, a batch of postcards, a folded leaflet: each one may take up a small corner of the sheet a large offset press can carry. Gang run printing fills the rest of that sheet with other jobs, so the press prints paid work instead of empty paper.
The sheet is planned before anything is printed
A gang run starts as a layout. The jobs are nested side by side and stacked down the sheet, arranged around their finished sizes, the quantity each buyer needs and the format the press will run. One plate may carry a dozen business cards, two postcards and a rack card in a single arrangement. The whole sheet is printed in one pass, then cut apart in finishing, and each loose piece goes to its own job.
Metallic print often brings to mind hot foil stamping: a heated die, a sheet of foil, pressure, and a bright shine pressed into the page. Cold foil reaches a similar visual result by a completely different route, one that runs inline on the printing press.
How cold foil transfers
The process starts with an adhesive printed onto the sheet, in exactly the shape of the metallic area. That adhesive is a printing unit's job, so it can carry fine detail and halftones like any other ink. A thin metallic foil film is then pressed against the wet adhesive as the sheet travels through the press. Where adhesive sits, the foil sticks. A UV lamp cures the adhesive inside the press, and the carrier film is stripped away with the foil left only where it was wanted.
Open a softcover book and look down the spine gutter and you will usually find glue. Nearly every softcover book on a shelf is perfect bound: the folded pages are milled at the spine, roughened, and held together by a single adhesive. Which adhesive depends on two names: EVA and PUR.
EVA, the workhorse hot melt
EVA stands for ethylene-vinyl acetate. It is a hot-melt adhesive, applied molten at high temperature, and it sets in seconds as it cools. That speed is why EVA dominates high-volume paperback production: a binding line can turn a pile of trimmed book blocks into finished books without waiting on a chemical cure.
When two shapes overlap in a print file, the software makes a quiet decision about what happens underneath. That decision is knockout or ov...
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