Definition
A hard, glass-like insulating film of silicon dioxide that forms on the electrical contact points of magnetos and other ignition components when silicone vapors are present in the engine compartment and are exposed to the high-temperature electrical arc at the contact surface. The glaze prevents the contacts from carrying current properly and causes ignition system malfunction.
Plain English
A glassy coating that builds up on the small electrical contact points inside a magneto when silicone fumes get burned by the spark. Once it forms, the contacts can no longer pass electricity reliably, so the ignition system stops working the way it should.
Context Anchor
Seen in aircraft engine maintenance, especially during cylinder inspections, engine break-in discussions, and troubleshooting for high oil use or low cylinder sealing.
Derivation
Silicon refers to the chemical element that forms the glassy deposit. Glaze comes from the Old English glaes (glass), describing a smooth, hard, glass-like coating. Together the term names exactly what forms on the contacts: a thin, glass-like layer of silicon compound.
Why Pilots Care
This ice is heavy, hard to remove, and changes how the wing produces lift.
Grounding Statement
A cylinder wall needs enough surface texture for the rings to seat; silicon glaze makes that surface too slick and hard.
Intuition Check
Do not read “glaze” as a protective finish here. Silicon glaze is not something you want on the cylinder wall; it is an unwanted condition that can prevent proper sealing.
Example Sentence 1
The mechanic suspected silicon glaze on the breaker points after the magneto began producing a weak and intermittent spark.
Example Sentence 2
Silicon glaze is harder to shed with de-icing boots than rime ice.