What is wemeling (distortion in old window glass)?
“Wemeling” is the Dutch term for the irregular distortion of the view through glass with a slightly curved or wavy surface. You mainly see it in old window glass: look through at an angle or move your head and straight lines outside seem to ripple.
Where does it come from?
Before float glass became standard in the second half of the twentieth century, window glass was made in other ways, including cylinder glass (blown cylinders that were cut open and flattened) and later machine-drawn sheet glass. The surface was never perfectly flat: small waves, variations in thickness and sometimes bubbles remained. Float glass solidifies on a bath of molten tin and is very flat, so it shows almost no distortion.
Why does it matter?
- Heritage value: the ripple in old panes contributes to the character of a historic facade, so old glass is kept wherever possible in listed buildings.
- Dating: waves, bubbles and tint help estimate the age of a window.
- Appearance: single panes replaced with float glass stand out through their flat, mirror-like reflection.
Practical tips
- Keep old glass: remove it carefully during painting or frame repairs and refit it. Old glass is often thinner and more brittle than modern glass.
- Replacement: in historic buildings choose restoration glass with a deliberately irregular surface. Insulating units with such glass on the outside also exist.
- Secondary glazing: to improve insulation without losing the old glass, add secondary glazing on the inside.
- Consent: for listed buildings, replacing glass may need consent from the local authority. Check before you start.
Related terms
- Glazing bar layout of historic windows
- Leaded glass
- Secondary glazed windows
- Restoration
- Glazing bar
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.