As with all lead products i.e. lead sheet, pipes, flashings, etc., the adhesive lead strips, which we use for our sealed units, are subject to oxidation. This ‘weathering’ process will form a naturally protective patina when exposed to the atmosphere.

This patina is a layer of highly insoluble lead salts, which gradually form on the lead surface to eventually give the familiar grey lead appearance. Examples of this effect can be seen on old leaded lights, such as in church windows.

During the initial stages of the oxidation process, lead can display various colours including blue, bronze and green. It is probable that such films are extremely thin and in fact have no intrinsic colour but appear coloured due to an interference effect Similar interference colours may be observed when oil is present on a wet road. Lead is most likely to appear coloured when placed indoors or in protected locations.

When lead comes into contact with moisture, rainwater, condensation etc. at early stage, discoloration, spotting and white powdery deposits (usually basic lead carbonate) can form and may ‘run-off’. The degree to which all these occur is governed by the environmental conditions, but with longer term weathering, the lead will take on its’ familiar appearance.

Investigations have shown that the patina formation follows the route: lead, lead oxide, basic lead carbonate, normal lead sulphite, and normal lead sulphate. The ‘run-off’ stage occurs when non-adherent basic lead carbonate is formed, usually through contact with moisture. Each of the stages in patina formation is adherent, highly insoluble lead salts and in practice, as these salts develop with weathering, they stifle the basic lead carbonate release. The final patina being approximately 30% normal lead sulphite, 60% normal lead sulphate and 10% normal lead carbonate. However, this can vary dependant upon location, time and airborne impurities.

Suggested after care

In the event that you experience an accelerated rate of oxidation directly after installation, you should make every effort to clean the ‘run-off’ deposits, as soon as possible. Failure to do so could result in the deposits drying onto the glass and becoming more difficult to clean. This effect can be compared to lime scale on a shower screen.
To clean the glass, simply use a water-based glass cleaner with a paper or cloth towel, whilst removing any stubborn stains with a household non-abrasive cream cleaner. Avoid agitating the surface of the lead, as much as possible, as this will slow down the weathering process.