Foundry pattern colour coding — identifying unmachined surfaces In standard pattern-marking practice, which colour is used to indicate surfaces that will be left unmachined on the final casting?

Introduction / Context:
Pattern colour coding conveys manufacturing intent to moulders and machinists. Consistent colour standards prevent costly errors during machining and core setting.

Given Data / Assumptions:

• Standard practice widely used in Indian and British foundries.
• Colours: red for machined surfaces, yellow for core prints, black often for unmachined surfaces.
• No special shop-specific variations assumed.

Concept / Approach:
Unmachined surfaces are typically marked black on the pattern, indicating that no stock is added and no finishing cut is planned. Red marks surfaces that need machining allowance. Core prints are frequently painted yellow to alert moulders to core placement and support.

Step-by-Step Solution:
Identify colour standards for machining vs. non-machining.Unmachined = black; Machined = red; Core print = yellow.Select “black colour”.

Verification / Alternative check:
Training charts and pattern-making manuals depict black for unmachined areas to avoid confusion during layout and fettling.

Why Other Options Are Wrong:

• Red colour: indicates machining allowance.
• Yellow colour: indicates core prints.
• Blue colour: used in some shops for loose pieces or special marks, not standard for unmachined surfaces.

Common Pitfalls:
Mixing shop-specific codes; always follow the plant’s official legend if it differs.

Final Answer:
black colour