Meaning, Materials and Operations of Colouring for SS 3

Class: SS 3
Term: First Term
Week: 10
Age: 14 years
Duration: 45 minutes
Subject: Metal Work
Topic: Colouring
Subject Matter: Meaning of colouring; Colouring materials e.g., hydrochloric acid, carbonic acid and ammonium sulphate etc; Coloring operations

Specific Objectives

By the end of the lesson, pupils/students should be able to:

Cognitive Domain

• Define metal colouring.
• State the importance of colouring in metalwork.
• List common materials used for metal colouring.
• Explain the function of various colouring materials.
• Describe different operations involved in colouring metals.

Affective Domain

• Appreciate the aesthetic and protective benefits of metal colouring.
• Observe safety precautions when handling colouring chemicals.
• Participate actively in discussions and practical demonstrations.

Psychomotor Domain

• Demonstrate basic colouring operations on metal samples.
• Apply appropriate colouring materials to achieve desired finishes.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Metalwork for Senior Secondary Schools, Book 3
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Samples of coloured metal pieces (e.g., brass, copper, steel)
• Small samples of hydrochloric acid, carbonic acid, ammonium sulphate (with appropriate safety containers)
• Safety goggles, gloves, and aprons
• Metal cleaning agents (e.g., degreaser)
• Brushes, sponges, or cloths for application
• Heating equipment (e.g., blowtorch, hot plate) for heat colouring
• Ventilated workshop area
• Whiteboard and markers

Rationale for the Lesson

This lesson is important for students to understand how to enhance the appearance and durability of metal products. It provides practical knowledge of various colouring techniques and the chemicals involved, which is essential for producing high-quality metalwork finishes. Understanding these processes also reinforces the importance of safety in the metalwork environment.

Prerequisite/Previous Knowledge

Students should have basic knowledge of metal properties, different types of metals, and fundamental metal finishing techniques such as filing, grinding, and polishing.

Lesson Content/Board Summary

Colouring

Meaning of Colouring

Colouring in metalwork refers to the process of altering the surface appearance of a metal to achieve a desired colour, finish, or protective layer. This can be done for aesthetic purposes, to differentiate metals, or to provide a degree of corrosion resistance.

Importance of Colouring

1. Aesthetics: Enhances the visual appeal of metal products, making them more attractive.
2. Identification: Helps in distinguishing between different types of metals or components.
3. Protection: Can provide a thin protective layer against corrosion or wear.
4. Value Addition: Increases the market value and desirability of finished metal items.

Colouring Materials

Various chemical solutions and compounds are used to create different colours on metal surfaces. Some common examples include:

1. Hydrochloric Acid (HCl): Used in some processes to clean metal surfaces before colouring or as part of a pickling solution to prepare the metal for oxidation or chemical reactions that produce colour.
2. Carbonic Acid (H₂CO₃): While not typically used directly as a colouring agent, it can be present in some solutions or contribute to surface reactions in specific atmospheric conditions, though less common than other acids in direct colouring.
3. Ammonium Sulphate ((NH₄)₂SO₄): Can be used in certain chemical baths to create specific patinas or surface colours on metals like copper or bronze, often in combination with other chemicals.
4. Potassium Sulphide (Liver of Sulphur): Commonly used to create antique finishes (browns, blacks) on copper, brass, and silver.
5. Ferric Chloride: Used for blackening steel and creating patinas on copper alloys.
6. Sodium Thiosulphate: Can be used in solutions for browning or blackening specific metals.
7. Copper Sulphate: Used to create a copper plating or a reddish-brown finish on steel.

Colouring Operations/Methods

The operations involved in colouring metals depend on the desired finish and the type of metal. Common methods include:

1. Surface Preparation:
   1. Cleaning: Removing grease, oil, dirt, and oxides from the metal surface using degreasers, abrasives, or acid pickling (e.g., using hydrochloric acid).
   2. Rinsing: Thoroughly washing the metal to remove all cleaning agents.
2. Chemical Immersion/Application:
   1. The prepared metal piece is immersed in a chemical solution (e.g., containing ammonium sulphate, potassium sulphide, or ferric chloride) or the solution is applied with a brush or sponge.
   2. The duration of immersion or contact time affects the intensity and shade of the colour.
   3. Chemical reactions occur on the metal surface, forming a coloured oxide layer or a chemical compound that imparts the desired colour.
3. Heat Colouring (Thermal Colouring):
   1. The metal is heated to a specific temperature, causing an oxide layer to form on the surface.
   2. Different temperatures produce different colours (e.g., on steel, blueing or straw colours).
   3. This method is often used for steel and can be done with a blowtorch or oven.
4. Electro-colouring (Anodizing):
   1. Primarily used for aluminium, where an electrolytic process creates a thick, porous oxide layer that can absorb dyes.
   2. This process provides both colour and enhanced corrosion resistance.
5. Finishing:
   1. After colouring, the metal may be rinsed again and dried.
   2. A protective clear lacquer, wax, or oil may be applied to seal the colour and prevent further oxidation or wear.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Observation, Practical Activity.

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Activating Prior Knowledge

Teacher’s Activity: The teacher asks students about different finishes they have seen on metal objects and if they know how these colours are achieved. The teacher then introduces the topic of metal colouring.

Pupils’ Activity: Students respond to questions and listen attentively to the introduction.

Learning Point: Introduction to metal colouring

Step 2: Meaning of Colouring

Time: 7 minutes

Teaching Skill: Explanation/Definition

Teacher’s Activity: The teacher explains the meaning of colouring in metalwork, using examples of coloured metal samples. The teacher also states the importance of colouring.

Pupils’ Activity: Students listen, observe the samples, and ask questions for clarification.

Learning Point: Meaning and importance of colouring

Step 3: Colouring Materials

Time: 8 minutes

Teaching Skill: Listing/Identification

Teacher’s Activity: The teacher lists and introduces various colouring materials, specifically mentioning hydrochloric acid, carbonic acid, and ammonium sulphate, and shows examples where possible (in safe containers). The teacher emphasises safety when handling these chemicals.

Pupils’ Activity: Students note down the materials and observe the samples, paying attention to safety warnings.

Learning Point: Identification of colouring materials

Step 4: Explanation of Colouring Materials

Time: 8 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher explains the role and application of each listed colouring material, discussing how they react with different metals to produce colours. The teacher reiterates safety measures.

Pupils’ Activity: Students listen, ask questions about the materials, and discuss their uses.

Learning Point: Function of colouring materials

Step 5: Colouring Operations

Time: 7 minutes

Teaching Skill: Description/Demonstration

Teacher’s Activity: The teacher describes the various steps involved in colouring operations, such as surface preparation, chemical application, heat colouring, and finishing. The teacher may perform a simple, safe demonstration of a colouring operation (e.g., applying a patina to copper if feasible and safe).

Pupils’ Activity: Students observe the demonstration, ask questions, and take notes on the operational steps.

Learning Point: Steps in colouring operations

Step 6: Guided Practice/Participation

Time: 5 minutes

Teaching Skill: Practical Application

Teacher’s Activity: Under strict supervision and with all safety gear, the teacher allows a few students to participate in a simple, controlled colouring exercise, such as cleaning a small metal piece or applying a mild, safe colouring agent.

Pupils’ Activity: Students participate in the practical exercise, following safety instructions carefully.

Learning Point: Practical colouring application

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. What is metal colouring?
2. Mention two reasons why metals are coloured.
3. List three materials used for metal colouring.
4. Describe one method of colouring metal.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding colouring concepts

Step 8: Note-Taking

Time: 4 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on the meaning, materials, and operations of colouring into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Recording lesson information

Step 9: Conclusion

Time: 1 minute

Teaching Skill: Consolidation

Teacher’s Activity: The teacher summarises the key points of the lesson, reminding students about the importance of safety in metal colouring. The teacher encourages students to explore more about different colouring techniques.

Pupils’ Activity: Students listen and reflect on the lesson.

Learning Point: Reinforcement of key concepts

Continuous Assessment/Further Study

Type: Homework

Instruction: Research and write short notes on the following:

1. The difference between colouring and plating in metalwork.
2. Two other chemicals used for colouring metals not discussed in class.
3. The safety precautions that must be taken when working with acids in a metalwork shop.

Lesson Keywords

• Colouring – Altering the surface appearance of metal.
• Hydrochloric Acid – A strong acid used for cleaning and pickling metals.
• Carbonic Acid – A weak acid, less commonly used directly for colouring.
• Ammonium Sulphate – A chemical compound used in some patination processes.
• Patinas – A thin layer that forms on the surface of metal, often a greenish or brownish colour, produced by oxidation or other chemical processes.
• Surface Preparation – The process of cleaning and treating a metal surface before colouring.

Differentiation

For weaker learners, provide simplified notes and focus on identifying the meaning and a few key materials. Pair them with stronger learners during practical demonstrations. For faster learners, encourage them to research advanced colouring techniques like anodizing or electroplating and present their findings to the class.

Suggested Lesson Videos

For further understanding, search YouTube for: “Metal colouring techniques SS3” or “Chemical patination of metals”.

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure all chemical samples are safely stored and clearly labelled. Prepare metal samples for demonstration and ensure the workshop is well-ventilated, with all necessary safety equipment (goggles, gloves, aprons) readily available. Begin by engaging students with real-world examples of coloured metals to spark their interest. When discussing colouring materials, strictly adhere to safety protocols, emphasising that students should never handle chemicals without direct supervision and proper protective gear. During the practical activity, keep it simple and highly controlled, focusing on a safe aspect like surface cleaning or applying a very mild, non-corrosive agent. Allow students to copy the Board Summary notes after the main teaching points have been covered and reviewed. Check for understanding frequently through questioning, especially regarding safety. Encourage all students to participate, providing extra support to those who struggle with the chemical concepts and challenging faster learners with additional research tasks.