---
title: "Paint and its constituents"
subject: "Engineering Chemistry"
chapter: 8
key: "semester_2/engineering_chemistry:paint-constituents"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/paint-constituents
site: BCT Engineering
---

# Paint and its constituents

Engineering Chemistry · Chapter 8: Lubricants and Paints

- Asked in: 2068 Magh, 2 marks
- Video: [Components of Paints](https://www.youtube.com/watch?v=kyjYsKfEz88) — Engineering Motive
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/paint-constituents
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-8

## Question

What is paint? Write three important constituents of paint.

## Short answer

Paint is a pigment dispersion in a drying oil. Key constituents: pigment provides colour and opacity; vehicle (drying oil) forms the film; thinner adjusts viscosity for application.

## Answer

**Paint** is a mechanical dispersion of pigment in a drying oil with thinner and other additives, used to protect and decorate surfaces.

#### Three important constituents
1. **Pigment:** a fine coloured powder that gives colour, opacity and strength, and protects against UV light. Examples: TiO₂ (white), ZnO, Fe₂O₃ (red), Cr₂O₃ (green), carbon black.
2. **Vehicle (drying oil):** the liquid medium, like linseed oil, that holds the pigment and forms a hard, tough, adherent film by oxidation and polymerisation on drying.
3. **Thinner (solvent):** turpentine or mineral spirit, which reduces viscosity for easy application and evaporates afterwards.

(Other additives: driers such as Pb/Mn/Co linoleates, extenders like barytes and plasticisers.)

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is paint?
   A. A clear solution of resin in volatile solvent with no pigment
   B. A mixture of cement and pigment in water
   C. A solution of bitumen in a solvent
   D. A dispersion of pigment in a drying oil with thinner, drier and additives, forming a protective, decorative film
   Answer: D. Paint is a mechanical dispersion of pigment in a drying oil (vehicle) with thinner, drier and additives; it dries to a thin film. (Key point: Definition of paint)

2. What does pigment do in a paint?
   A. Dissolves the oil
   B. Gives colour and opacity and protects against UV light
   C. Evaporates after application
   D. Speeds up drying
   Answer: B. Pigment is a fine coloured powder giving colour, opacity and strength. (Key point: Pigment)

3. How does the vehicle (drying oil) form the film?
   A. By evaporating completely
   B. By dissolving the pigment
   C. By reacting with the thinner to form gas
   D. By oxidation and polymerisation on drying
   Answer: D. The drying oil hardens by oxidation and polymerisation. (Key point: Vehicle)

4. What is the role of the thinner?
   A. To give colour
   B. To reduce viscosity for easy application, then evaporate
   C. To form the hard film
   D. To speed up oxidation
   Answer: B. Turpentine or mineral spirit thins the paint and evaporates. (Key point: Thinner)

## Related in other subjects

- [Pointing, plastering defects, oil paint constituents](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apointing-plaster-defects-paint) — Building Technology, chapter 9, asked 2×