Saturday, 8 November 2014

Stained glass construction details


Leaded glass windows are made waterproof and rigid by means of the 'cement' - a black putty-like compound that is forced between the glass and the lead.  For consistency and reliability we always used a commercial products, and not a 'home brewed' recipe or regular putty that has been coloured - we consider that these cheaper alternatives to 'the real thing' as being inferior.


There are 3 main producers of lead in the EU, which comes in 2m lengths in cases of 25kg.  There are minor producers, sometimes using soft un-alloyed lead which we find less suitable. We have a preference for the lead from Germany.  This shows 6mm wide lead with a ‘half round’ profile, as well as 12 and 16mm, which is generally used at the borders.  We also use 5, 8 and 10mm.


solder for stained glass and leaded lightsWe generally use solder that comprises 50% lead and 50% tin.  Before the joints are made by melting the solder onto and into them, the lead is rubbed with tallow – in the form of (wickless) ‘candles’ (essentially beef fat – stearic acid) which acts as a flux, enabling the molten solder to flow and coat and fill the lead, thus making the joint.  The solder melts at around 200 degrees C.


Leaded lights and stained glass windows have a tendency to 'bow' and this needs to be offset by various supporting devices.  They are often fitted with support bars, usually aligned with the lead lines so they are less conspicuous.  It is also possible to introduce thin steel strips next to the 'heart' of the lead, edge-wise to the glass, and sometimes pieced through intersecting pieces of lead.  This internal reinforcement works best when the lead is wider - 8mm  minimum or better still 10.

Support bars and tie-wires
This shows the detail of the way in which leaded glass panels may be supported, strengthened and made more durable by use of support bars, set into the frame on the inside and secured to the panels by means of copper tie-wires soldered to the panel.  The copper tarnishes with time, although it may be painted.  The chemistry between the steel of the bar, the copper and the lead does mean that over time the bars will begin to develop a coating of rust.  This is a very traditional method of adding support.

Retaining a leaded panel with putty

This shows how leaded glass panels fitted into frames that will then be sealed with putty are retained.  (This is in contrast to panel retained with timber beading)  Putty alone is insufficient to hold the panel in the frame, because of the weight.  So the traditional way to hold it in is with tacks, hammered in such that the head just depresses into the border lead.  Generally we use 16mm steel tacks.  In older work the tacks are often found to be in copper or maybe bronze, but these are very hard to come by.  Once tacked in, a filet of putty is applied to cover and seal the gap, much as for normal single glazing in wooden frames.

Labels: ,