The Rainbow That Will Not Wipe Off
A strange oily rainbow appears across the middle of a double-glazed window.
Glass cleaner does nothing. Neither does polishing the outside pane. The coloured rings appear to sit inside the sealed unit itself.
They are not grease marks. The pattern can be an optical effect called Newton’s rings.
Two Panes Getting Too Close
A sealed double-glazed unit uses two panes separated around the perimeter by a spacer bar. The cavity between them contains air or insulating gas.
Pressure inside that sealed cavity changes with temperature and atmospheric conditions. The glass naturally deflects slightly as those pressures change.
Problems start once the two panes bow far enough to nearly touch or physically contact each other around the centre of the unit. Newton’s rings appear as roughly circular or elliptical coloured bands around that contact area.
Light Creates the Oil-Slick Effect
The rainbow comes from light rather than anything deposited on the glass.
Light reflects from the two extremely close glass surfaces. Tiny differences in the gap alter how those reflected light waves combine, producing the coloured interference pattern visible from the room.
Large units, unsuitable cavity widths, inadequate glass thickness or manufacturing pressure problems can contribute to excessive pane deflection.
Actual Newton’s rings should not be confused with every coloured reflection visible in modern glazing. Other interference effects can occur in otherwise sound insulated glass units.
The Glass Unit Needs Checking
Clean both accessible glass surfaces first to rule out ordinary residue.
Look at the pattern from several angles. Concentric rainbow rings concentrated around the centre of the unit deserve closer inspection, particularly alongside visible inward bowing of the panes.
Glass-to-glass contact cannot be repaired with cleaner, gasket adjustment or resealing around the window frame. The sealed unit itself needs assessing for the correct glass thickness, cavity and overall specification.
Continued contact can also damage the internal glass surfaces and reduce the insulating performance of the unit.
Trade Counter Supplies
An oily rainbow inside double glazing can reveal far more than a dirty pane.
Bring your sealed-unit measurements and glass specification into DWC Trade Windows at 78 Alma Road, Bournemouth. Our trade counter team can help with replacement double-glazed units and the correct glazing components for the job.
Call us on 01202 533126 to discuss replacement glass in Bournemouth.
