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What is micrometer engineers marking blue?

What is engineer's blue?

Jenny calipers are used to take accurate measurements.

On some metals, lines or arcs that have been scribed using a jenny caliper may not be clearly visible. Using an oil-based paste called ‘engineer’s blue’ can solve this problem.


When engineer’s blue is mixed with methylated spirits, it forms a quick drying blue liquid known as marking blue or layout blue.


This is applied to the workpiece using a paintbrush before a jenny caliper is used to either locate the centre point or scribe a line parallel to the edge.


Following the application of the engineer’s blue solution, scribed lines will be more easily visible, as the blue colour provides a good contrast with the metal.


After the part has been machined, micrometer engineer’s marking blue can be removed with a solvent such as methylated spirits and a cloth.

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