Standards and paper formats
A standard is an agreed rule. In printing, standards for paper sizes, type sizes, colours and quality let printers, designers and machine makers work together. The world paper standard is ISO 216 (the A, B and C series).
In the A-series the long side divided by the short side is always √2 ≈ 1.414. A0 is 841 × 1189 mm (1 m²). Halving the long side gives the next size, and the shape does not change. A1 594 × 841, A2 420 × 594, A3 297 × 420, A4 210 × 297, A5 148 × 210. Each step halves the area.
Paper weight is in grams per square metre (gsm). A4 at 80 gsm weighs about 5 g. Thicker paper (200 gsm) feels like card.
Typefaces and text composition
A typeface is a family of letter designs. Serif letters have small strokes (feet) at the ends and look traditional. Sans-serif letters are plain and look modern. Monospace letters all have the same width.
Size is measured in points: 1 point = 1/72 inch ≈ 0.353 mm. Body text is usually 9 to 12 pt, headings are larger. Leading is the space between lines (about 120% of the size). Text composition (typesetting) means choosing the font, size, line length, alignment and spacing so the text is easy to read: not too many words in a line (about 50 to 75 characters).
Page layout rules
A good page has margins (white space around), a grid of columns, a clear hierarchy (heading, subheading, body), and alignment (things line up). Pictures are placed on the grid and have a caption. Leave white space; it rests the eye. Keep a consistent style across pages. For a printed book the inside margin is wider, since part of it goes into the binding. Allow bleed (3 mm of extra colour past the edge) if a picture touches the edge, so a small cutting shift does not show a white line.
Job technical sheet and quality control
A job technical sheet lists everything the printer needs: customer, product, size, number of copies, paper type and gsm, number of colours, finishing (cut, fold, staple, varnish), delivery date and price. It is the plan for the whole job.
Quality control of materials: check the paper (size, gsm, grain direction, moisture, whiteness), the ink (colour, thickness), and the plates (clean, no scratches). Check the first printed sheet against the proof, and check again during the run. Faults found early save paper.
Substrates, plates, inks and finishing materials
A substrate is what we print on: paper, card, film, fabric or metal sheet. Coated paper is smooth and makes sharp pictures; uncoated paper is rough and good for writing. Printing plates carry the image: in offset printing, an aluminium plate that holds ink only on the image areas. Inks: the four process inks C (cyan), M (magenta), Y (yellow), K (black) print as tiny dots; the eye mixes them into all colours. Special (spot) inks, like gold, are used for logos. Auxiliary materials: dampening solution, blankets, cleaning solvents and powder. Finishing materials: varnish and lamination for shine and protection, thread, glue and wire for binding, and covers.
Try it: halve a sheet
Take an A4 sheet and fold it in half across the long side. It is now A5. Measure: 148 × 210 mm. Divide the long side by the short: 210 ÷ 148 ≈ 1.42. It is still the same shape. In the 3D, last step, switch ink layers on and off and describe what you see: cyan + yellow = green, magenta + yellow = red, all three = a dark brown.
Key formulas and definitions
- A-series: long side ÷ short side = √2 ≈ 1.414
- Area of A(n+1) = area of An ÷ 2; A0 = 1 m²
- Sheet mass (g) = area (m²) × gsm
- 1 point = 1/72 inch ≈ 0.353 mm
- Ink set: C + M + Y + K
Worked examples
1. How many A4 sheets can be cut from one A0 sheet?
A0 → 2 A1 → 4 A2 → 8 A3 → 16 A4. So 16.
2. Find the mass of one A4 sheet of 80 gsm paper.
Area = 0.21 × 0.297 = 0.0624 m². Mass = 0.0624 × 80 ≈ 5 g.
3. What is 12 pt in millimetres?
12 × 0.353 = 4.24 mm.
4. Why does a 3 mm bleed help?
The cutting blade can shift a little. If the colour runs 3 mm past the cut line, a small shift never shows a white edge.
Common mistakes
- Saying A4 is half of A3 by length. It is half by area: the long side of A3 becomes the short side of A4.
- Forgetting bleed on pictures that touch the edge.
- Choosing text that is too small or lines that are too long to read.
- Thinking K means "kolor". K means the key plate, which prints black.